diff --git a/examples/algorithms/retry.hpp b/examples/algorithms/retry.hpp
index 2fc3e1c6f..c4d34488f 100644
--- a/examples/algorithms/retry.hpp
+++ b/examples/algorithms/retry.hpp
@@ -134,7 +134,7 @@ struct _retry_sender
   using _value = stdexec::completion_signatures<stdexec::set_value_t(Ts...)>;
 
   template <class Self, class... Env>
-  static consteval auto get_completion_signatures() -> stdexec::transform_completion_signatures<
+  static consteval auto get_completion_signatures() -> stdexec::__transform_completion_signatures_t<
     stdexec::completion_signatures_of_t<S&, Env...>,
     stdexec::completion_signatures<stdexec::set_error_t(std::exception_ptr)>,
     _value,
diff --git a/examples/algorithms/then.hpp b/examples/algorithms/then.hpp
index 4d3f33dcd..4288a0bee 100644
--- a/examples/algorithms/then.hpp
+++ b/examples/algorithms/then.hpp
@@ -70,7 +70,7 @@ struct _then_sender
     stdexec::completion_signatures<stdexec::set_value_t(std::invoke_result_t<F, Args...>)>;
 
   template <class... Env>
-  using _completions_t = stdexec::transform_completion_signatures<
+  using _completions_t = stdexec::__transform_completion_signatures_t<
     stdexec::completion_signatures_of_t<S, Env...>,
     stdexec::completion_signatures<stdexec::set_error_t(std::exception_ptr)>,
     _set_value_t>;
diff --git a/include/exec/asio/use_sender.hpp b/include/exec/asio/use_sender.hpp
index 302e53899..d276f0ac4 100644
--- a/include/exec/asio/use_sender.hpp
+++ b/include/exec/asio/use_sender.hpp
@@ -166,9 +166,9 @@ namespace experimental::execution::asio
 
     template <typename Signatures>
     using completion_signatures =
-      ::STDEXEC::transform_completion_signatures<Signatures,
-                                                 ::STDEXEC::completion_signatures<>,
-                                                 transform_set_value_t>;
+      ::STDEXEC::__transform_completion_signatures_t<Signatures,
+                                                     ::STDEXEC::completion_signatures<>,
+                                                     transform_set_value_t>;
 
     template <typename Sender>
     struct sender
diff --git a/include/exec/async_scope.hpp b/include/exec/async_scope.hpp
index e8873b6a0..49de3041b 100644
--- a/include/exec/async_scope.hpp
+++ b/include/exec/async_scope.hpp
@@ -444,7 +444,7 @@ namespace experimental::execution
     using __decay_error_t = completion_signatures<set_error_t(__decay_t<_Ty>)>;
 
     template <class _Sender, class _Env>
-    using __future_completions_t = transform_completion_signatures_of<
+    using __future_completions_t = __transform_completion_signatures_of_t<
       _Sender,
       __env_t<_Env>,
       completion_signatures<set_stopped_t(), set_error_t(std::exception_ptr)>,
diff --git a/include/exec/completion_signatures.hpp b/include/exec/completion_signatures.hpp
index 0a10f23a2..3ab764b15 100644
--- a/include/exec/completion_signatures.hpp
+++ b/include/exec/completion_signatures.hpp
@@ -58,19 +58,25 @@ namespace experimental::execution
   //! by combining explicitly provided signature types with those deduced from pointer
   //! arguments.
   //!
-  //! @tparam ExplicitSigs Explicitly specified completion signature types.
-  //! @tparam DeducedSigs Completion signature types to be deduced from the function arguments.
-  //! @param unnamed Pointer arguments (unused) used for type deduction of DeducedSigs.
+  //! \tparam ExplicitSigs Explicitly specified completion signature types. Must be a pack
+  //!                      of function types, the returns types of which must be one of
+  //!                      \c set_value_t, \c set_error_t, or \c set_stopped_t.
+  //! \tparam DeducedSigs  Completion signature types to be deduced from the function
+  //!                      arguments.
+  //! \param unnamed       Pointer arguments (unused) for type deduction of
+  //!                      \c DeducedSigs. Must be a pack of function pointer types, the
+  //!                      returns types of which must be one of \c set_value_t,
+  //!                      \c set_error_t, or \c set_stopped_t.
   //!
-  //! @return An instance of `STDEXEC::completion_signatures` containing the combined
+  //! \return An instance of \c STDEXEC::completion_signatures containing the combined
   //!         signatures.
   //!
-  //! @note This is a `consteval` function, meaning it is only callable in constant evaluation
-  //!       contexts (compile-time). It always returns a default-constructed instance of the result
-  //!       type.
+  //! \note This is a \c consteval function, meaning it is only callable in constant
+  //!       evaluation contexts (compile-time). It always returns a default-constructed
+  //!       instance of the result type.
   //!
-  //! @note The function uses pointer arguments for type deduction without requiring actual object
-  //!       instances.
+  //! \note The function uses pointer arguments for type deduction without requiring
+  //!       actual object instances.
   template <class... ExplicitSigs, class... DeducedSigs>
   [[nodiscard]]
   consteval auto make_completion_signatures(DeducedSigs*...) noexcept
@@ -95,33 +101,134 @@ namespace experimental::execution
 
   //////////////////////////////////////////////////////////////////////////////////////////////////
   // transform_completion_signatures
+
   template <class _SetTag>
   using keep_completion = STDEXEC::__keep_completion<_SetTag>;
 
   using ignore_completion = STDEXEC::__ignore_completion;
 
-  template <class _SetTag, class _Fn, class... _AlgoTag>
-  using transform_arguments = STDEXEC::__transform_arguments<_SetTag, _Fn, _AlgoTag...>;
+  template <class _SetTag, template <class> class _Fn, class... _AlgoTag>
+  using transform_arguments =
+    STDEXEC::__transform_arguments<_SetTag, STDEXEC::__q1<_Fn>, _AlgoTag...>;
 
   template <class _SetTag, class... _AlgoTag>
   using decay_arguments = STDEXEC::__decay_arguments<_SetTag, _AlgoTag...>;
 
-  template <class _Completions,
-            class _ValueFn   = keep_completion<STDEXEC::set_value_t>,
-            class _ErrorFn   = keep_completion<STDEXEC::set_error_t>,
-            class _StoppedFn = keep_completion<STDEXEC::set_stopped_t>,
-            class _ExtraSigs = STDEXEC::completion_signatures<>>
-  consteval auto transform_completion_signatures(_Completions,
-                                                 _ValueFn   __value_fn   = {},
-                                                 _ErrorFn   __error_fn   = {},
-                                                 _StoppedFn __stopped_fn = {},
-                                                 _ExtraSigs              = {})
+  //! \brief Transforms completion signatures using provided transformation functions.
+  //!
+  //! This consteval function transforms a set of completion signatures by applying
+  //! custom transformation functions to value, error, and stopped completion cases.
+  //! The result can be augmented with additional extra signatures.
+  //!
+  //! \tparam Completions The input completion signatures to transform. Must be a
+  //!                     specialization of \c STDEXEC::completion_signatures.
+  //! \tparam ValueFn     Function object that transforms set_value_t completions.
+  //!                     Defaults to keep_completion<set_value_t>.
+  //! \tparam ErrorFn     Function object that transforms set_error_t completions.
+  //!                     Defaults to keep_completion<set_error_t>.
+  //! \tparam StoppedFn   Function object that transforms set_stopped_t completions.
+  //!                     Defaults to keep_completion<set_stopped_t>.
+  //! \tparam ExtraSigs   Additional completion signatures to append to the result.
+  //!                     Must be a specialization of \c STDEXEC::completion_signatures.
+  //!                     Defaults to \c STDEXEC::completion_signatures().
+  //!
+  //! \param completions  The input completion signatures object.
+  //! \param value_fn     Value transformation function instance.
+  //! \param error_fn     Error transformation function instance.
+  //! \param stopped_fn   Stopped transformation function instance.
+  //! \param extra_sigs   Extra signatures to append to the result.
+  //!
+  //! \return A transformed completion_signatures object combining the transformed
+  //!         input signatures with the extra signatures.
+  //!
+  //! \par Example
+  //!
+  //! The following example demonstrates how to use \c transform_completion_signatures
+  //! to compute the completion signatures of the \c then sender.
+  //!
+  //! \code{.cpp}
+  //! namespace ex = STDEXEC;
+  //!
+  //! // A helper function to transform the value types of the child sender into the value
+  //! // types of the then sender.
+  //! template <class Fn, class... Args>
+  //! consteval auto _transform_values()
+  //! {
+  //!   if constexpr (!std::invocable<Fn, Args...>)
+  //!   {
+  //!     // If Fn cannot be invoked with the given arguments, produce a compile-time
+  //!     // error.
+  //!     return exec::throw_compile_time_error<
+  //!       WHAT(FUNCTION_IS_NOT_CALLABLE_WITH_THE_GIVEN_ARGUMENTS),
+  //!       WHERE(IN_ALGORITHM, then_t),
+  //!       WITH_FUNCTION(Fn),
+  //!       WITH_ARGUMENTS(Args...)>();
+  //!   }
+  //!   else
+  //!   {
+  //!     // transform the value types of the child sender into the value types of the
+  //!     // then sender by applying Fn to them.
+  //!     using result_t         = std::invoke_result_t<Fn, Args...>;
+  //!     constexpr bool is_void = std::is_void_v<result_t>;
+  //!     constexpr bool nothrow = std::is_nothrow_invocable_v<Fn, Args...>;
+  //!     if constexpr (is_void && nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t()>();
+  //!     }
+  //!     else if constexpr (is_void && !nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(),
+  //!                                        set_error_t(std::exception_ptr)>();
+  //!     }
+  //!     else if constexpr (!is_void && nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(result_t)>();
+  //!     }
+  //!     else /* !is_void && !nothrow */
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(result_t),
+  //!                                        set_error_t(std::exception_ptr)>();
+  //!     }
+  //!   }
+  //! }
+  //!
+  //! template <class Child, class Fn>
+  //! struct then_sender
+  //! {
+  //!   using sender_concept = ex::sender_t;
+  //!
+  //!   template <class Self, class... Env>
+  //!   static consteval auto get_completion_signatures()
+  //!   {
+  //!     // Compute the completion signatures of the child sender, and then transform
+  //!     // them into the completion signatures of the `then` sender.
+  //!     auto child_completions = exec::get_child_completion_signatures<Self, Child, Env...>();
+  //!     auto value_fn = []<class... Args>() { return _transform_values<Fn, Args...>(); };
+  //!
+  //!     return exec::transform_completion_signatures(child_completions, value_fn);
+  //!   }
+  //!
+  //!   // ...
+  //! };
+  //! \endcode
+  //!
+  //! \note This function is evaluated at compile-time (consteval).
+  template <class Completions,
+            class ValueFn   = keep_completion<STDEXEC::set_value_t>,
+            class ErrorFn   = keep_completion<STDEXEC::set_error_t>,
+            class StoppedFn = keep_completion<STDEXEC::set_stopped_t>,
+            class ExtraSigs = STDEXEC::completion_signatures<>>
+  consteval auto transform_completion_signatures(Completions,
+                                                 ValueFn   value_fn   = {},
+                                                 ErrorFn   error_fn   = {},
+                                                 StoppedFn stopped_fn = {},
+                                                 ExtraSigs            = {})
   {
-    return STDEXEC::__transform_completion_signatures(_Completions{},
-                                                      __value_fn,
-                                                      __error_fn,
-                                                      __stopped_fn,
-                                                      _ExtraSigs{});
+    return STDEXEC::__transform_completion_signatures(Completions{},
+                                                      value_fn,
+                                                      error_fn,
+                                                      stopped_fn,
+                                                      ExtraSigs{});
   }
 }  // namespace experimental::execution
 
diff --git a/include/exec/detail/shared.hpp b/include/exec/detail/shared.hpp
index 96751e24c..44b490349 100644
--- a/include/exec/detail/shared.hpp
+++ b/include/exec/detail/shared.hpp
@@ -133,13 +133,13 @@ namespace experimental::execution::__shared
   ////////////////////////////////////////////////////////////////////////////////////////
   template <class _CvSender, class _Env>
   using __result_variant_t =
-    __transform_completion_signatures_t<__completion_signatures_of_t<_CvSender, _Env>,
-                                        __mbind_front_q<__decayed_tuple, set_value_t>::__f,
-                                        __mbind_front_q<__decayed_tuple, set_error_t>::__f,
-                                        __tuple<set_stopped_t>,
-                                        __munique<__qq<__variant>>::__f,
-                                        __tuple<set_error_t, std::exception_ptr>,
-                                        __tuple<set_stopped_t>>;
+    __transform_reduce_completion_signatures_t<__completion_signatures_of_t<_CvSender, _Env>,
+                                               __mbind_front_q<__decayed_tuple, set_value_t>::__f,
+                                               __mbind_front_q<__decayed_tuple, set_error_t>::__f,
+                                               __tuple<set_stopped_t>,
+                                               __munique<__qq<__variant>>::__f,
+                                               __tuple<set_error_t, std::exception_ptr>,
+                                               __tuple<set_stopped_t>>;
 
   ////////////////////////////////////////////////////////////////////////////////////////
   template <class _CvChild, class _Env>
@@ -461,12 +461,12 @@ namespace experimental::execution::__shared
   };
 
   template <class _Cv, class _CvSender, class _Env>
-  using __make_completions_t = __try_make_completion_signatures<
+  using __make_completions_t = __transform_completion_signatures_of_t<
     _CvSender,
     __env_t<_Env>,
     completion_signatures<set_error_t(__mcall1<_Cv, std::exception_ptr>), set_stopped_t()>,
-    __mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_value_t>>>,
-    __mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_error_t>>>>;
+    __mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_value_t>>>::template __f,
+    __mtransform<_Cv, __mcompose<__qq<completion_signatures>, __qf<set_error_t>>>::template __f>;
 
   // split completes with const T&. ensure_started completes with T&&.
   template <class _Tag>
diff --git a/include/exec/into_tuple.hpp b/include/exec/into_tuple.hpp
index 8bccb1c31..2a7fd6f7c 100644
--- a/include/exec/into_tuple.hpp
+++ b/include/exec/into_tuple.hpp
@@ -53,7 +53,7 @@ namespace experimental::execution
       STDEXEC::completion_signatures<set_error_t(std::exception_ptr), set_value_t(_Tuple)>;
 
     template <class _Sender, class... _Env>
-    using __completions_t = transform_completion_signatures<
+    using __completions_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<_Sender, _Env...>,
       __minvoke_q<__tuple_completions_t, __result_tuple_t<_Sender, _Env...>>,
       __mconst<STDEXEC::completion_signatures<>>::__f>;
diff --git a/include/exec/just_from.hpp b/include/exec/just_from.hpp
index 953b0b5fc..7f898091e 100644
--- a/include/exec/just_from.hpp
+++ b/include/exec/just_from.hpp
@@ -115,7 +115,7 @@ namespace experimental::execution
     {
       template <class Fn>
       using __f = STDEXEC::__concat_completion_signatures_t<STDEXEC::__call_result_t<Fn, _probe_fn>,
-                                                            STDEXEC::__eptr_completion>;
+                                                            STDEXEC::__eptr_completion_t>;
     };
 
     template <class Fn>
diff --git a/include/exec/libdispatch_queue.hpp b/include/exec/libdispatch_queue.hpp
index 3a7f79d7b..a77eefcb1 100644
--- a/include/exec/libdispatch_queue.hpp
+++ b/include/exec/libdispatch_queue.hpp
@@ -258,14 +258,14 @@ namespace experimental::execution
                                  STDEXEC::__mbind_front_q<bulk_non_throwing_t, Fun, Shape>,
                                  STDEXEC::__q<STDEXEC::__mand>>::value,
         STDEXEC::completion_signatures<>,
-        STDEXEC::__eptr_completion>;
+        STDEXEC::__eptr_completion_t>;
 
       template <class... Tys>
       using set_value_t =
         STDEXEC::completion_signatures<STDEXEC::set_value_t(STDEXEC::__decay_t<Tys>...)>;
 
       template <class Self, class... Env>
-      using _completions_t = STDEXEC::transform_completion_signatures<
+      using _completions_t = STDEXEC::__transform_completion_signatures_t<
         STDEXEC::__completion_signatures_of_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
         with_error_invoke_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
         set_value_t>;
diff --git a/include/exec/materialize.hpp b/include/exec/materialize.hpp
index 397eecc56..f57b089ef 100644
--- a/include/exec/materialize.hpp
+++ b/include/exec/materialize.hpp
@@ -95,7 +95,7 @@ namespace experimental::execution
       using __materialize_error = completion_signatures<set_value_t(set_error_t, _Err)>;
 
       template <class _Self, class... _Env>
-      using __completions_t = __transform_completion_signatures_t<
+      using __completions_t = __transform_reduce_completion_signatures_t<
         __completion_signatures_of_t<__copy_cvref_t<_Self, _Sender>, _Env...>,
         __materialize_value,
         __materialize_error,
@@ -202,7 +202,7 @@ namespace experimental::execution
       using __dematerialize_value = completion_signatures<__decay_t<_Tag>(_Args...)>;
 
       template <class _Self, class... _Env>
-      using __completions_t = transform_completion_signatures<
+      using __completions_t = __transform_completion_signatures_t<
         __completion_signatures_of_t<__copy_cvref_t<_Self, _Sender>, _Env...>,
         completion_signatures<>,
         __mtry_q<__dematerialize_value>::template __f>;
diff --git a/include/exec/repeat_n.hpp b/include/exec/repeat_n.hpp
index 1abad7cc1..29fbfa1e9 100644
--- a/include/exec/repeat_n.hpp
+++ b/include/exec/repeat_n.hpp
@@ -197,15 +197,15 @@ namespace experimental::execution
     using __error_t = completion_signatures<set_error_t(__decay_t<_Error>)>;
 
     template <typename _Sender, typename... _Env>
-    using __with_eptr_completion_t = __eptr_completion_unless<
+    using __with_eptr_completion_t = __eptr_completion_unless_t<__mbool<
       __cmplsigs::__partitions_of_t<
         __completion_signatures_of_t<_Sender, _Env...>>::__nothrow_decay_copyable::__errors::value
-      && (__nothrow_connectable<_Sender, __receiver_archetype<_Env>> && ...)>;
+      && (__nothrow_connectable<_Sender, __receiver_archetype<_Env>> && ...)>>;
 
     template <class _Child, class... _Env>
-    using __completions_t = STDEXEC::transform_completion_signatures<
+    using __completions_t = STDEXEC::__transform_completion_signatures_t<
       __completion_signatures_of_t<_Child &, _Env...>,
-      STDEXEC::transform_completion_signatures<
+      STDEXEC::__transform_completion_signatures_t<
         __completion_signatures_of_t<STDEXEC::schedule_result_t<trampoline_scheduler>, _Env...>,
         __with_eptr_completion_t<_Child, _Env...>,
         __cmplsigs::__default_set_value,
diff --git a/include/exec/repeat_until.hpp b/include/exec/repeat_until.hpp
index 497ad8f7f..d0ac876b2 100644
--- a/include/exec/repeat_until.hpp
+++ b/include/exec/repeat_until.hpp
@@ -283,9 +283,9 @@ namespace experimental::execution
           }
           else
           {
-            constexpr bool __has_nothrow_connect =
-              (__nothrow_connectable<__child_t, __receiver_archetype<_Env>> || ...);
-            constexpr auto __eptr_sigs    = __eptr_completion_unless<__has_nothrow_connect>();
+            using __has_nothrow_connect_t =
+              __mbool<(__nothrow_connectable<__child_t, __receiver_archetype<_Env>> || ...)>;
+            constexpr auto __eptr_sigs    = __eptr_completion_unless_t<__has_nothrow_connect_t>();
             constexpr auto __bouncer_sigs = exec::transform_completion_signatures(
               get_completion_signatures<__bouncer_t, _Env...>(),
               exec::ignore_completion());  // drop the set_value_t() completion from the
diff --git a/include/exec/sequence.hpp b/include/exec/sequence.hpp
index 75c4c5fb9..7c8365962 100644
--- a/include/exec/sequence.hpp
+++ b/include/exec/sequence.hpp
@@ -258,9 +258,9 @@ namespace experimental::execution
         }
         else
         {
-          using __env_t          = STDEXEC::__mfront<Env..., STDEXEC::env<>>;
-          using __rcvr_t         = STDEXEC::__receiver_archetype<__env_t>;
-          constexpr bool nothrow = (STDEXEC::__nothrow_connectable<Senders, __rcvr_t> && ...);
+          using __env_t               = STDEXEC::__mfront<Env..., STDEXEC::env<>>;
+          using __rcvr_t              = STDEXEC::__receiver_archetype<__env_t>;
+          constexpr bool __is_nothrow = (STDEXEC::__nothrow_connectable<Senders, __rcvr_t> && ...);
 
           // The completions of the sequence sender are the error and stopped completions of all the
           // child senders plus the value completions of the last child sender.
@@ -272,7 +272,7 @@ namespace experimental::execution
               STDEXEC::get_completion_signatures<Senders, Env...>(),
               exec::ignore_completion())...,
             STDEXEC::get_completion_signatures<STDEXEC::__mback<Senders...>, Env...>(),
-            STDEXEC::__eptr_completion_unless<nothrow>());
+            STDEXEC::__eptr_completion_unless_t<STDEXEC::__mbool<__is_nothrow>>());
         }
       }
 
diff --git a/include/exec/sequence/ignore_all_values.hpp b/include/exec/sequence/ignore_all_values.hpp
index 3d6a9fce7..66fc279d3 100644
--- a/include/exec/sequence/ignore_all_values.hpp
+++ b/include/exec/sequence/ignore_all_values.hpp
@@ -249,7 +249,7 @@ namespace experimental::execution
     };
 
     template <class _Sigs>
-    using __result_variant_ = __transform_completion_signatures_t<
+    using __result_variant_ = __transform_reduce_completion_signatures_t<
       _Sigs,
       __mconst<__mlist<>>::__f,
       __mcompose_q<__mlist, __mbind_front_q<__decayed_tuple, set_error_t>::__f>::__f,
diff --git a/include/exec/sequence/merge_each.hpp b/include/exec/sequence/merge_each.hpp
index 8a4b04b53..af5c162df 100644
--- a/include/exec/sequence/merge_each.hpp
+++ b/include/exec/sequence/merge_each.hpp
@@ -659,7 +659,7 @@ namespace experimental::execution
       template <class _Self, class... _Env>
       static consteval auto get_completion_signatures() noexcept
       {
-        using __result_t = STDEXEC::transform_completion_signatures<
+        using __result_t = STDEXEC::__transform_completion_signatures_t<
           STDEXEC::__completion_signatures_of_t<_NestedValueSender, _Env...>,
           STDEXEC::completion_signatures<STDEXEC::set_stopped_t()>,
           STDEXEC::__cmplsigs::__default_set_value,
diff --git a/include/exec/static_thread_pool.hpp b/include/exec/static_thread_pool.hpp
index 4425a4a65..9bc475370 100644
--- a/include/exec/static_thread_pool.hpp
+++ b/include/exec/static_thread_pool.hpp
@@ -1266,13 +1266,13 @@ namespace experimental::execution
                                _is_nothrow_bulk_fn<Shape, Fun>,
                                __q<__mand>>::value,
                completion_signatures<>,
-               __eptr_completion>;
+               __eptr_completion_t>;
 
       template <class... Tys>
       using _set_value_t = completion_signatures<set_value_t(STDEXEC::__decay_t<Tys>...)>;
 
       template <class Self, class... Env>
-      using _completions_t = STDEXEC::transform_completion_signatures<
+      using _completions_t = STDEXEC::__transform_completion_signatures_t<
         __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
         _with_error_invoke_t<__copy_cvref_t<Self, Sender>, Env...>,
         _set_value_t>;
diff --git a/include/exec/thread_pool_base.hpp b/include/exec/thread_pool_base.hpp
index 98d73a927..22299f82b 100644
--- a/include/exec/thread_pool_base.hpp
+++ b/include/exec/thread_pool_base.hpp
@@ -377,7 +377,7 @@ namespace experimental::execution
           STDEXEC::completion_signatures<STDEXEC::set_value_t(STDEXEC::__decay_t<Tys>...)>;
 
         template <class Self, class... Env>
-        using _completion_signatures_t = STDEXEC::transform_completion_signatures<
+        using _completion_signatures_t = STDEXEC::__transform_completion_signatures_t<
           STDEXEC::__completion_signatures_of_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
           _with_error_invoke_t<Self, Env...>,
           _set_value_t>;
diff --git a/include/exec/unless_stop_requested.hpp b/include/exec/unless_stop_requested.hpp
index 8988a935f..2d6ff219f 100644
--- a/include/exec/unless_stop_requested.hpp
+++ b/include/exec/unless_stop_requested.hpp
@@ -37,10 +37,10 @@ namespace experimental::execution
 
     template <class _Sender, class _Env>
     using __completions_t =
-      transform_completion_signatures<__completion_signatures_of_t<_Sender, _Env>,
-                                      __if_c<__unstoppable_env<_Env>,
-                                             completion_signatures<>,
-                                             completion_signatures<set_stopped_t()>>>;
+      __transform_completion_signatures_t<__completion_signatures_of_t<_Sender, _Env>,
+                                          __if_c<__unstoppable_env<_Env>,
+                                                 completion_signatures<>,
+                                                 completion_signatures<set_stopped_t()>>>;
 
     template <class _CvChild, class _Receiver>
     struct __opstate
diff --git a/include/exec/when_any.hpp b/include/exec/when_any.hpp
index 2e6a7e801..fa31f4dd6 100644
--- a/include/exec/when_any.hpp
+++ b/include/exec/when_any.hpp
@@ -60,7 +60,7 @@ namespace experimental::execution
       using __f = __mtry_q<__concat_completion_signatures_t>::__f<
         __eptr_completion_unless_t<__all_value_args_nothrow_decay_copyable<_CvSenders...>>,
         completion_signatures<set_stopped_t()>,
-        __transform_completion_signatures_t<
+        __transform_reduce_completion_signatures_t<
           __completion_signatures_of_t<_CvSenders, __env_t<_Env>...>,
           __as_rvalues,
           __as_error,
diff --git a/include/nvexec/multi_gpu_context.cuh b/include/nvexec/multi_gpu_context.cuh
index b1c43a86d..704c83f3b 100644
--- a/include/nvexec/multi_gpu_context.cuh
+++ b/include/nvexec/multi_gpu_context.cuh
@@ -118,8 +118,7 @@ namespace nv::execution
 
         template <class Receiver>
         [[nodiscard]]
-        auto connect(Receiver rcvr) const & noexcept(__nothrow_move_constructible<Receiver>)
-          -> opstate<Receiver>
+        auto connect(Receiver rcvr) const & noexcept -> opstate<Receiver>
         {
           return opstate<Receiver>(static_cast<Receiver&&>(rcvr));
         }
diff --git a/include/nvexec/nvtx.cuh b/include/nvexec/nvtx.cuh
index 60e40ea0c..0c5bd4de2 100644
--- a/include/nvexec/nvtx.cuh
+++ b/include/nvexec/nvtx.cuh
@@ -102,11 +102,7 @@ namespace nv::execution
       template <class Receiver>
       using receiver_t = receiver<Kind, Receiver>;
 
-      template <class Self, class Env>
-      using _completions_t = __try_make_completion_signatures<__copy_cvref_t<Self, Sender>, Env>;
-
       template <__decays_to<nvtx_sender> Self, STDEXEC::receiver Receiver>
-        requires receiver_of<Receiver, _completions_t<Self, env_of_t<Receiver>>>
       STDEXEC_EXPLICIT_THIS_BEGIN(auto connect)(this Self&& self, Receiver rcvr)
         -> stream_opstate_t<__copy_cvref_t<Self, Sender>, receiver_t<Receiver>, Receiver>
       {
@@ -119,9 +115,9 @@ namespace nv::execution
       STDEXEC_EXPLICIT_THIS_END(connect)
 
       template <__decays_to<nvtx_sender> Self, class Env>
-      static consteval auto get_completion_signatures() -> _completions_t<Self, Env>
+      static consteval auto get_completion_signatures()
       {
-        return {};
+        return STDEXEC::get_completion_signatures<__copy_cvref_t<Self, Sender>, Env>();
       }
 
       auto get_env() const noexcept -> stream_sender_attrs<Sender>
diff --git a/include/nvexec/stream/algorithm_base.cuh b/include/nvexec/stream/algorithm_base.cuh
index 072aa65f9..c5b6a54ab 100644
--- a/include/nvexec/stream/algorithm_base.cuh
+++ b/include/nvexec/stream/algorithm_base.cuh
@@ -101,7 +101,7 @@ namespace nv::execution::_strm::__algo_range_init_fun
     using _set_value_t = __minvoke_q<__mfirst, DerivedSender, Range>::template _set_value_t<Range>;
 
     template <class Self, class... Env>
-    using _completions_t = STDEXEC::transform_completion_signatures<
+    using _completions_t = STDEXEC::__transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       completion_signatures<set_error_t(cudaError_t)>,
       __mtry_q<_set_value_t>::template __f>;
diff --git a/include/nvexec/stream/bulk.cuh b/include/nvexec/stream/bulk.cuh
index 53550f206..3b39d6c40 100644
--- a/include/nvexec/stream/bulk.cuh
+++ b/include/nvexec/stream/bulk.cuh
@@ -123,7 +123,7 @@ namespace nv::execution::_strm
     using _set_value_t = completion_signatures<set_value_t(Tys...)>;
 
     template <class Self, class... Env>
-    using _completion_signatures_t = transform_completion_signatures<
+    using _completion_signatures_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       _set_error_t,
       _set_value_t>;
@@ -359,7 +359,7 @@ namespace nv::execution::_strm
     using _set_value_t = completion_signatures<set_value_t(Tys...)>;
 
     template <class Self, class... Env>
-    using _completion_signatures_t = transform_completion_signatures<
+    using _completion_signatures_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       _set_error_t,
       _set_value_t>;
diff --git a/include/nvexec/stream/continues_on.cuh b/include/nvexec/stream/continues_on.cuh
index 08e89fc7b..a7ee8f260 100644
--- a/include/nvexec/stream/continues_on.cuh
+++ b/include/nvexec/stream/continues_on.cuh
@@ -245,7 +245,7 @@ namespace nv::execution::_strm
     STDEXEC_EXPLICIT_THIS_END(connect)
 
     template <__decays_to<continues_on_sender> Self, class... Env>
-    static consteval auto get_completion_signatures() -> transform_completion_signatures<
+    static consteval auto get_completion_signatures() -> __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       completion_signatures<set_error_t(cudaError_t)>,
       _trnsfr::value_completions_t,
diff --git a/include/nvexec/stream/ensure_started.cuh b/include/nvexec/stream/ensure_started.cuh
index f67536c6a..78c610464 100644
--- a/include/nvexec/stream/ensure_started.cuh
+++ b/include/nvexec/stream/ensure_started.cuh
@@ -389,12 +389,12 @@ namespace nv::execution::_strm
     using _set_error_t = completion_signatures<set_error_t(__decay_t<Ty>)>;
 
     template <class Self, class... Env>
-    static consteval auto get_completion_signatures() -> __try_make_completion_signatures<
+    static consteval auto get_completion_signatures() -> __transform_completion_signatures_of_t<
       Sender,
       _ensure_started::env_t,
       completion_signatures<set_error_t(cudaError_t), set_stopped_t()>,
-      __q<_set_value_t>,
-      __q<_set_error_t>>
+      _set_value_t,
+      _set_error_t>
     {
       return {};
     }
diff --git a/include/nvexec/stream/launch.cuh b/include/nvexec/stream/launch.cuh
index 1f3c98398..35b29e785 100644
--- a/include/nvexec/stream/launch.cuh
+++ b/include/nvexec/stream/launch.cuh
@@ -118,9 +118,9 @@ namespace nv::execution
 
       template <class Fun, class CvSender, class... Env>
       using completions_t =
-        transform_completion_signatures<__completion_signatures_of_t<CvSender, Env...>,
-                                        completion_signatures<set_error_t(std::exception_ptr)>,
-                                        __mbind_front_q<_set_value_t, Fun>::template __f>;
+        __transform_completion_signatures_t<__completion_signatures_of_t<CvSender, Env...>,
+                                            completion_signatures<set_error_t(std::exception_ptr)>,
+                                            __mbind_front_q<_set_value_t, Fun>::template __f>;
     }  // namespace _launch
 
     template <class Sender, class Fun>
diff --git a/include/nvexec/stream/let_xxx.cuh b/include/nvexec/stream/let_xxx.cuh
index 9a69c1da7..37b8d62b8 100644
--- a/include/nvexec/stream/let_xxx.cuh
+++ b/include/nvexec/stream/let_xxx.cuh
@@ -85,7 +85,7 @@ namespace nv::execution::_strm
     struct __tfx_signal_fn<Set, Set(Args...)>
     {
       template <class Fun, class... StreamEnv>
-      using __f = transform_completion_signatures<
+      using __f = __transform_completion_signatures_t<
         __completion_signatures_of_t<__minvoke<_mk_result_sender<Fun>, Args...>, StreamEnv...>,
         completion_signatures<set_error_t(cudaError_t)>>;
     };
diff --git a/include/nvexec/stream/schedule_from.cuh b/include/nvexec/stream/schedule_from.cuh
index 9b9b814f3..d189e25e4 100644
--- a/include/nvexec/stream/schedule_from.cuh
+++ b/include/nvexec/stream/schedule_from.cuh
@@ -136,7 +136,7 @@ namespace nv::execution
       using _set_error_t = completion_signatures<set_error_t(__decay_t<Ty>)>;
 
       template <class Self, class... Env>
-      using _completions_t = transform_completion_signatures<
+      using _completions_t = __transform_completion_signatures_t<
         __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
         completion_signatures<set_stopped_t(), set_error_t(cudaError_t)>,
         _set_value_t,
diff --git a/include/nvexec/stream/split.cuh b/include/nvexec/stream/split.cuh
index 25dbbafe8..8b592e21d 100644
--- a/include/nvexec/stream/split.cuh
+++ b/include/nvexec/stream/split.cuh
@@ -353,16 +353,19 @@ namespace nv::execution::_strm
     template <class Ty>
     using _set_error_t = completion_signatures<set_error_t(__decay_t<Ty> const &)>;
 
-    using completion_signatures = __try_make_completion_signatures<
-      Sender,
-      STDEXEC::prop<get_stop_token_t, inplace_stop_token>,
-      STDEXEC::completion_signatures<set_error_t(cudaError_t const &)>,
-      __q<_set_value_t>,
-      __q<_set_error_t>>;
-
-    template <receiver_of<completion_signatures> Receiver>
-    auto connect(Receiver rcvr) const & noexcept(__nothrow_move_constructible<Receiver>)
-      -> opstate_t<Receiver>
+    template <class>
+    static consteval auto get_completion_signatures()
+    {
+      return STDEXEC::__transform_completion_signatures_of_t<
+        Sender,
+        STDEXEC::prop<get_stop_token_t, inplace_stop_token>,
+        STDEXEC::completion_signatures<set_error_t(cudaError_t const &)>,
+        _set_value_t,
+        _set_error_t>();
+    }
+
+    template <receiver Receiver>
+    auto connect(Receiver rcvr) const & noexcept -> opstate_t<Receiver>
     {
       return opstate_t<Receiver>{static_cast<Receiver&&>(rcvr), sh_state_};
     }
diff --git a/include/nvexec/stream/then.cuh b/include/nvexec/stream/then.cuh
index 389d6f8e5..80f442222 100644
--- a/include/nvexec/stream/then.cuh
+++ b/include/nvexec/stream/then.cuh
@@ -165,7 +165,7 @@ namespace nv::execution::_strm
     using _set_value_t = __set_value_from_t<Fun, Args...>;
 
     template <class Self, class... Env>
-    using _completions_t = transform_completion_signatures<
+    using _completions_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       __error_completions_t<Self, Env...>,
       _set_value_t,
diff --git a/include/nvexec/stream/upon_error.cuh b/include/nvexec/stream/upon_error.cuh
index 813be2b49..f3342a99e 100644
--- a/include/nvexec/stream/upon_error.cuh
+++ b/include/nvexec/stream/upon_error.cuh
@@ -151,7 +151,7 @@ namespace nv::execution::_strm
     using _set_error_t = __set_value_from_t<Fun, Error>;
 
     template <class Self, class... Env>
-    using completion_signatures = transform_completion_signatures<
+    using completion_signatures = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       completion_signatures<set_error_t(cudaError_t)>,
       __cmplsigs::__default_set_value,
diff --git a/include/nvexec/stream/upon_stopped.cuh b/include/nvexec/stream/upon_stopped.cuh
index 959ffe309..a10888a68 100644
--- a/include/nvexec/stream/upon_stopped.cuh
+++ b/include/nvexec/stream/upon_stopped.cuh
@@ -137,7 +137,7 @@ namespace nv::execution::_strm
     using receiver_t = _upon_stopped::receiver<Receiver, Fun>;
 
     template <class Self, class... Env>
-    using completion_signatures = transform_completion_signatures<
+    using completion_signatures = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<Self, Sender>, Env...>,
       __with_error_invoke_t<__mbind_front_q<__callable_error_t, upon_stopped_t>,
                             set_stopped_t,
diff --git a/include/nvexec/stream/when_all.cuh b/include/nvexec/stream/when_all.cuh
index 66a395a54..6f6780dc5 100644
--- a/include/nvexec/stream/when_all.cuh
+++ b/include/nvexec/stream/when_all.cuh
@@ -88,12 +88,12 @@ namespace nv::execution::_strm
       requires(valid_child_sender<Senders, Env...> && ...)
     struct completions<__mlist<Env...>, Senders...>
     {
-      using non_values_t =
-        __minvoke_q<__concat_completion_signatures_t,
-                    completion_signatures<set_error_t(cudaError_t), set_stopped_t()>,
-                    transform_completion_signatures<__completion_signatures_of_t<Senders, Env...>,
-                                                    completion_signatures<>,
-                                                    __mconst<completion_signatures<>>::__f>...>;
+      using non_values_t = __minvoke_q<
+        __concat_completion_signatures_t,
+        completion_signatures<set_error_t(cudaError_t), set_stopped_t()>,
+        __transform_completion_signatures_t<__completion_signatures_of_t<Senders, Env...>,
+                                            completion_signatures<>,
+                                            __mconst<completion_signatures<>>::__f>...>;
 
       using values_t = __minvoke<__mconcat<__qf<set_value_t>>,
                                  __value_types_t<__completion_signatures_of_t<Senders, Env...>,
diff --git a/include/nvexec/stream_context.cuh b/include/nvexec/stream_context.cuh
index 14e669b92..05a99d68c 100644
--- a/include/nvexec/stream_context.cuh
+++ b/include/nvexec/stream_context.cuh
@@ -136,8 +136,7 @@ namespace nv::execution
         {}
 
         template <class Receiver>
-        auto connect(Receiver rcvr) const & noexcept(__nothrow_move_constructible<Receiver>)
-          -> opstate<Receiver>
+        auto connect(Receiver rcvr) const & noexcept -> opstate<Receiver>
         {
           return opstate<Receiver>(static_cast<Receiver&&>(rcvr), env_.ctx_);
         }
diff --git a/include/stdexec/__detail/__associate.hpp b/include/stdexec/__detail/__associate.hpp
index c22b53013..79b175b2a 100644
--- a/include/stdexec/__detail/__associate.hpp
+++ b/include/stdexec/__detail/__associate.hpp
@@ -246,7 +246,7 @@ namespace STDEXEC
 
       template <class _Sender, class... _Env>
       static consteval auto __get_completion_signatures()  //
-        -> transform_completion_signatures<
+        -> __transform_completion_signatures_t<
           __completion_signatures_of_t<__wrap_sender_of_t<_Sender>, _Env...>,
           completion_signatures<set_stopped_t()>>
       {
diff --git a/include/stdexec/__detail/__bulk.hpp b/include/stdexec/__detail/__bulk.hpp
index 041071cb6..c0b0410ef 100644
--- a/include/stdexec/__detail/__bulk.hpp
+++ b/include/stdexec/__detail/__bulk.hpp
@@ -168,10 +168,10 @@ namespace STDEXEC
                           typename __bulk_traits<_AlgoTag>::template __fun_curried<_Fun, _Shape>>,
              __q<__mand>>,
            completion_signatures<>,
-           __eptr_completion>;
+           __eptr_completion_t>;
 
     template <class _AlgoTag, class _Fun, class _Shape, class _CvSender, class... _Env>
-    using __completion_signatures = transform_completion_signatures<
+    using __completion_signatures = __transform_completion_signatures_t<
       __completion_signatures_of_t<_CvSender, _Env...>,
       __with_error_invoke_t<_AlgoTag, _Fun, _Shape, _CvSender, _Env...>>;
 
diff --git a/include/stdexec/__detail/__continues_on.hpp b/include/stdexec/__detail/__continues_on.hpp
index 809ddcf5c..29daade62 100644
--- a/include/stdexec/__detail/__continues_on.hpp
+++ b/include/stdexec/__detail/__continues_on.hpp
@@ -64,12 +64,12 @@ namespace STDEXEC
 
     template <class _Scheduler, class _Completions, class... _Env>
     using __completions_impl_t = __mtry_q<__concat_completion_signatures_t>::__f<
-      __transform_completion_signatures_t<_Completions,
-                                          __decay_value_sig,
-                                          __decay_error_sig,
-                                          set_stopped_t (*)(),
-                                          __completion_signature_ptrs_t>,
-      transform_completion_signatures<
+      __transform_reduce_completion_signatures_t<_Completions,
+                                                 __decay_value_sig,
+                                                 __decay_error_sig,
+                                                 set_stopped_t (*)(),
+                                                 __completion_signature_ptrs_t>,
+      __transform_completion_signatures_t<
         __completion_signatures_of_t<schedule_result_t<_Scheduler>, _Env...>,
         __eptr_completion_unless_t<__nothrow_decay_copyable_results_t<_Completions>>,
         __mconst<completion_signatures<>>::__f>>;
diff --git a/include/stdexec/__detail/__into_variant.hpp b/include/stdexec/__detail/__into_variant.hpp
index d2939a8ac..0f011bf8b 100644
--- a/include/stdexec/__detail/__into_variant.hpp
+++ b/include/stdexec/__detail/__into_variant.hpp
@@ -50,7 +50,7 @@ namespace STDEXEC
       completion_signatures<set_value_t(_Variant), set_error_t(std::exception_ptr)>;
 
     template <class _Sender, class... _Env>
-    using __completions = transform_completion_signatures<
+    using __completions = __transform_completion_signatures_t<
       __completion_signatures_of_t<_Sender, _Env...>,
       __minvoke_q<__variant_completions, __variant_t<_Sender, _Env...>>,
       __mconst<completion_signatures<>>::__f>;
diff --git a/include/stdexec/__detail/__let.hpp b/include/stdexec/__detail/__let.hpp
index bdf17961a..716053c64 100644
--- a/include/stdexec/__detail/__let.hpp
+++ b/include/stdexec/__detail/__let.hpp
@@ -165,18 +165,18 @@ namespace STDEXEC
     struct __transform_signal_fn
     {
       template <class... _Args>
-      static constexpr bool __nothrow_connect_v =
+      using __nothrow_connect_t = __mbool<
         __nothrow_decay_copyable<_Args...> && __nothrow_callable<_Fun, __decay_t<_Args>&...>
         && (__nothrow_connectable<__mcall<__result_sender_fn<_SetTag, _Fun, _JoinEnv2>, _Args...>,
                                   __receiver_archetype<_JoinEnv2>>
-            && ...);
+            && ...)>;
 
       template <class... _Args>
       using __f = __mcall<__mtry_q<__concat_completion_signatures_t>,
                           __completion_signatures_of_t<
                             __mcall<__result_sender_fn<_SetTag, _Fun, _JoinEnv2...>, _Args...>,
                             _JoinEnv2...>,
-                          __eptr_completion_unless<__nothrow_connect_v<_Args...>>>;
+                          __eptr_completion_unless_t<__nothrow_connect_t<_Args...>>>;
     };
 
     template <class _LetTag, class _Fun, class _CvSender, class... _Env>
diff --git a/include/stdexec/__detail/__parallel_scheduler.hpp b/include/stdexec/__detail/__parallel_scheduler.hpp
index 6dcb39f3b..cf16ccb8f 100644
--- a/include/stdexec/__detail/__parallel_scheduler.hpp
+++ b/include/stdexec/__detail/__parallel_scheduler.hpp
@@ -606,7 +606,7 @@ namespace STDEXEC
   {
     /// Meta-function that returns the completion signatures of `this`.
     template <class _Self, class... _Env>
-    using __completions_t = transform_completion_signatures<
+    using __completions_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<__copy_cvref_t<_Self, _Previous>, _Env...>,
       completion_signatures<set_error_t(std::exception_ptr)>>;
 
diff --git a/include/stdexec/__detail/__stopped_as_optional.hpp b/include/stdexec/__detail/__stopped_as_optional.hpp
index 6eb24b1d4..43e4f49b4 100644
--- a/include/stdexec/__detail/__stopped_as_optional.hpp
+++ b/include/stdexec/__detail/__stopped_as_optional.hpp
@@ -72,7 +72,7 @@ namespace STDEXEC
           using _Completions = decltype(__completions);
           if constexpr (__single_value_sender<__child_of<_Self>, _Env...>)
           {
-            return transform_completion_signatures<
+            return __transform_completion_signatures_t<
               _Completions,
               completion_signatures<set_error_t(std::exception_ptr)>,
               __set_value_t,
diff --git a/include/stdexec/__detail/__task.hpp b/include/stdexec/__detail/__task.hpp
index 7151a7bc7..074aef85a 100644
--- a/include/stdexec/__detail/__task.hpp
+++ b/include/stdexec/__detail/__task.hpp
@@ -178,7 +178,7 @@ namespace STDEXEC
     using scheduler_type   = __minvoke_or_q<__task::__scheduler_type, task_scheduler, _Env>;
     using stop_source_type = __minvoke_or_q<__task::__stop_source_type, inplace_stop_source, _Env>;
     using stop_token_type  = decltype(__declval<stop_source_type>().get_token());
-    using error_types      = __minvoke_or_q<__task::__error_types, __eptr_completion, _Env>;
+    using error_types      = __minvoke_or_q<__task::__error_types, __eptr_completion_t, _Env>;
 
     constexpr task(task&& __that) noexcept
       : __coro_(std::exchange(__that.__coro_, {}))
diff --git a/include/stdexec/__detail/__task_scheduler.hpp b/include/stdexec/__detail/__task_scheduler.hpp
index 170f24959..e9f732c86 100644
--- a/include/stdexec/__detail/__task_scheduler.hpp
+++ b/include/stdexec/__detail/__task_scheduler.hpp
@@ -536,7 +536,7 @@ namespace STDEXEC
                                                           __decay_arguments<set_value_t>(),
                                                           {},
                                                           {},
-                                                          __eptr_completion());
+                                                          __eptr_completion_t());
       }
 
       [[nodiscard]]
diff --git a/include/stdexec/__detail/__then.hpp b/include/stdexec/__detail/__then.hpp
index f95feadee..8a59d22f7 100644
--- a/include/stdexec/__detail/__then.hpp
+++ b/include/stdexec/__detail/__then.hpp
@@ -36,7 +36,7 @@ namespace STDEXEC
     using __on_not_callable = __mbind_front_q<__callable_error_t, then_t>;
 
     template <class _Fun, class _CvSender, class... _Env>
-    using __completions_t = transform_completion_signatures<
+    using __completions_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<_CvSender, _Env...>,
       __with_error_invoke_t<__on_not_callable, set_value_t, _Fun, _CvSender, _Env...>,
       __mbind_front<__mtry_catch_q<__set_value_from_t, __on_not_callable>, _Fun>::template __f>;
diff --git a/include/stdexec/__detail/__transform_completion_signatures.hpp b/include/stdexec/__detail/__transform_completion_signatures.hpp
index 3860a5e95..cd510f55d 100644
--- a/include/stdexec/__detail/__transform_completion_signatures.hpp
+++ b/include/stdexec/__detail/__transform_completion_signatures.hpp
@@ -56,9 +56,10 @@ namespace STDEXEC
   concept __well_formed_completions = bool(
     __cmplsigs::__well_formed_completions_helper<_Completions>);
 
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  // __for_each_completion_signature_t
   namespace __cmplsigs
   {
-    //////////////////////////////////////////////////////////////////////////////////////////////////
     template <template <class...> class _Tuple, class _Tag, class... _Args>
     constexpr auto __for_each_sig(_Tag (*)(_Args...)) -> _Tuple<_Tag, _Args...>;
 
@@ -70,12 +71,12 @@ namespace STDEXEC
               template <class...> class _Variant,
               class... _More,
               class... _What>
-    constexpr auto __for_each_completion_signature_fn(_ERROR_<_What...> **) -> _ERROR_<_What...>;
+    constexpr auto __for_each_sigs(__undefined<_ERROR_<_What...>> *) -> _ERROR_<_What...>;
     template <template <class...> class _Tuple,
               template <class...> class _Variant,
               class... _More,
               class... _Sigs>
-    constexpr auto __for_each_completion_signature_fn(completion_signatures<_Sigs...> **)
+    constexpr auto __for_each_sigs(__undefined<completion_signatures<_Sigs...>> *)
       -> _Variant<__for_each_sig_t<_Sigs, _Tuple>..., _More...>;
   }  // namespace __cmplsigs
 
@@ -84,12 +85,15 @@ namespace STDEXEC
             template <class...> class _Variant,
             class... _More>
   using __for_each_completion_signature_t =
-    decltype(__cmplsigs::__for_each_completion_signature_fn<_Tuple, _Variant, _More...>(
-      static_cast<_Sigs **>(nullptr)));
+    decltype(__cmplsigs::__for_each_sigs<_Tuple, _Variant, _More...>(
+      static_cast<__undefined<_Sigs> *>(nullptr)));
 
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  // __transform_reduce_completion_signatures_t
+  // __transform_completion_signatures_t
+  // __transform_completion_signatures_of_t
   namespace __cmplsigs
   {
-    ////////////////////////////////////////////////////////////////////////////////////////////////
     template <template <class...> class _SetVal,
               template <class...> class _SetErr,
               class _SetStp,
@@ -118,7 +122,7 @@ namespace STDEXEC
               template <class...> class _Variant,
               class... _More,
               class... _What>
-    constexpr auto __transform_sigs_fn(_ERROR_<_What...> **) -> _ERROR_<_What...>;
+    constexpr auto __transform_reduce_sigs(__undefined<_ERROR_<_What...>> *) -> _ERROR_<_What...>;
 
     template <template <class...> class _SetVal,
               template <class...> class _SetErr,
@@ -126,8 +130,17 @@ namespace STDEXEC
               template <class...> class _Variant,
               class... _More,
               class... _Sigs>
-    constexpr auto __transform_sigs_fn(completion_signatures<_Sigs...> **)
+    constexpr auto __transform_reduce_sigs(__undefined<completion_signatures<_Sigs...>> *)
       -> _Variant<__transform_sig_t<_Sigs, _SetVal, _SetErr, _SetStp>..., _More...>;
+
+    template <class... _Values>
+    using __default_set_value = completion_signatures<set_value_t(_Values...)>;
+
+    template <class... _Error>
+    using __default_set_error = completion_signatures<set_error_t(_Error...)>;
+
+    template <class _Tag, class... _Args>
+    using __default_completion = completion_signatures<_Tag(_Args...)>;
   }  // namespace __cmplsigs
 
   template <class _Sigs,
@@ -136,13 +149,40 @@ namespace STDEXEC
             class _SetStp,
             template <class...> class _Variant,
             class... _More>
+  using __transform_reduce_completion_signatures_t =
+    decltype(__cmplsigs::__transform_reduce_sigs<_SetVal, _SetErr, _SetStp, _Variant, _More...>(
+      static_cast<__undefined<_Sigs> *>(nullptr)));
+
+  template <class _Sigs,
+            class _MoreSigs                           = completion_signatures<>,
+            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
+            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
+            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
   using __transform_completion_signatures_t =
-    decltype(__cmplsigs::__transform_sigs_fn<_SetVal, _SetErr, _SetStp, _Variant, _More...>(
-      static_cast<_Sigs **>(nullptr)));
+    __transform_reduce_completion_signatures_t<_Sigs,
+                                               _ValueTransform,
+                                               _ErrorTransform,
+                                               _StoppedSigs,
+                                               __mtry_q<__concat_completion_signatures_t>::__f,
+                                               _MoreSigs>;
+
+  template <class _Sndr,
+            class _Env                                = env<>,
+            class _MoreSigs                           = completion_signatures<>,
+            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
+            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
+            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
+  using __transform_completion_signatures_of_t =
+    __transform_completion_signatures_t<completion_signatures_of_t<_Sndr, _Env>,
+                                        _MoreSigs,
+                                        _ValueTransform,
+                                        _ErrorTransform,
+                                        _StoppedSigs>;
 
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  // __gather_completion_signatures_t
   namespace __cmplsigs
   {
-    ////////////////////////////////////////////////////////////////////////////////////////////////
     template <class _WantedTag, bool = true>
     struct __gather_sigs_fn;
 
@@ -154,13 +194,13 @@ namespace STDEXEC
                 template <class...> class _Else,
                 template <class...> class _Variant,
                 class... _More>
-      using __f =
-        __transform_completion_signatures_t<_Sigs,
-                                            _Then,
-                                            __mbind_front_q<_Else, set_error_t>::template __f,
-                                            _Else<set_stopped_t>,
-                                            _Variant,
-                                            _More...>;
+      using __f = __transform_reduce_completion_signatures_t<
+        _Sigs,
+        _Then,
+        __mbind_front_q<_Else, set_error_t>::template __f,
+        _Else<set_stopped_t>,
+        _Variant,
+        _More...>;
     };
 
     template <>
@@ -171,13 +211,13 @@ namespace STDEXEC
                 template <class...> class _Else,
                 template <class...> class _Variant,
                 class... _More>
-      using __f =
-        __transform_completion_signatures_t<_Sigs,
-                                            __mbind_front_q<_Else, set_value_t>::template __f,
-                                            _Then,
-                                            _Else<set_stopped_t>,
-                                            _Variant,
-                                            _More...>;
+      using __f = __transform_reduce_completion_signatures_t<
+        _Sigs,
+        __mbind_front_q<_Else, set_value_t>::template __f,
+        _Then,
+        _Else<set_stopped_t>,
+        _Variant,
+        _More...>;
     };
 
     template <>
@@ -188,13 +228,13 @@ namespace STDEXEC
                 template <class...> class _Else,
                 template <class...> class _Variant,
                 class... _More>
-      using __f =
-        __transform_completion_signatures_t<_Sigs,
-                                            __mbind_front_q<_Else, set_value_t>::template __f,
-                                            __mbind_front_q<_Else, set_error_t>::template __f,
-                                            _Then<>,
-                                            _Variant,
-                                            _More...>;
+      using __f = __transform_reduce_completion_signatures_t<
+        _Sigs,
+        __mbind_front_q<_Else, set_value_t>::template __f,
+        __mbind_front_q<_Else, set_error_t>::template __f,
+        _Then<>,
+        _Variant,
+        _More...>;
     };
 
     template <class _WantedTag>
@@ -207,15 +247,6 @@ namespace STDEXEC
                 class...>
       using __f = _Error;
     };
-
-    template <class... _Values>
-    using __default_set_value = completion_signatures<set_value_t(_Values...)>;
-
-    template <class... _Error>
-    using __default_set_error = completion_signatures<set_error_t(_Error...)>;
-
-    template <class _Tag, class... _Args>
-    using __default_completion = completion_signatures<_Tag(_Args...)>;
   }  // namespace __cmplsigs
 
   template <class _Sigs,
@@ -224,98 +255,16 @@ namespace STDEXEC
             template <class...> class _Else,
             template <class...> class _Variant,
             class... _More>
-  using __gather_completion_signatures_t = __cmplsigs::__gather_sigs_fn<
-    _WantedTag,
-    __ok<_Sigs>>::template __f<_Sigs, _Then, _Else, _Variant, _More...>;
-
-  /////////////////////////////////////////////////////////////////////////////
-  // transform_completion_signatures
-  // ==========================
-
-  // `transform_completion_signatures` takes a sender, and environment, and a bunch of other
-  // template arguments for munging the completion signatures of a sender in interesting ways.
-
-  //  ```c++
-  //  template <class... Args>
-  //    using __default_set_value = completion_signatures<set_value_t(Args...)>;
-
-  //  template <class Err>
-  //    using __default_set_error = completion_signatures<set_error_t(Err)>;
-
-  //  template <
-  //    class Completions,
-  //    class AdditionalSigs = completion_signatures<>,
-  //    template <class...> class SetValue = __default_set_value,
-  //    template <class> class SetError = __default_set_error,
-  //    class SetStopped = completion_signatures<set_stopped_t()>>
-  //  using transform_completion_signatures =
-  //    completion_signatures< ... >;
-  //  ```
-
-  //  * `SetValue` : an alias template that accepts a set of value types and returns an instance of
-  //    `completion_signatures`.
-
-  //  * `SetError` : an alias template that accepts an error types and returns a an instance of
-  //    `completion_signatures`.
-
-  //  * `SetStopped` : an instantiation of `completion_signatures` with a list of completion
-  //    signatures `Sigs...` to the added to the list if the sender can complete with a stopped
-  //    signal.
-
-  //  * `AdditionalSigs` : an instantiation of `completion_signatures` with a list of completion
-  //    signatures `Sigs...` to the added to the list unconditionally.
-
-  //  `transform_completion_signatures` does the following:
-
-  //  * Let `VCs...` be a pack of the `completion_signatures` types in the `__typelist` named by
-  //    `value_types_of_t<Sndr, Env, SetValue, __typelist>`, and let `Vs...` be the concatenation of
-  //    the packs that are template arguments to each `completion_signature` in `VCs...`.
-
-  //  * Let `ECs...` be a pack of the `completion_signatures` types in the `__typelist` named by
-  //    `error_types_of_t<Sndr, Env, __errorlist>`, where `__errorlist` is an alias template such
-  //    that `__errorlist<Ts...>` names `__typelist<SetError<Ts>...>`, and let `Es...` be the
-  //    concatenation of the packs that are the template arguments to each `completion_signature` in
-  //    `ECs...`.
-
-  //  * Let `Ss...` be an empty pack if `sends_stopped<Sndr, Env>` is `false`; otherwise, a pack
-  //    containing the template arguments of the `completion_signatures` instantiation named by
-  //    `SetStopped`.
-
-  //  * Let `MoreSigs...` be a pack of the template arguments of the `completion_signatures`
-  //    instantiation named by `AdditionalSigs`.
-
-  //  Then `transform_completion_signatures<Completions, AdditionalSigs, SetValue, SetError,
-  //  SendsStopped>` names the type `completion_signatures< Sigs... >` where `Sigs...` is the unique
-  //  set of types in `[Vs..., Es..., Ss..., MoreSigs...]`.
-
-  //  If any of the above type computations are ill-formed, `transform_completion_signatures<Sndr,
-  //  Env, AdditionalSigs, SetValue, SetError, SendsStopped>` is ill-formed.
-  template <class _Sigs,
-            class _MoreSigs                           = completion_signatures<>,
-            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
-            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
-            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
-  using transform_completion_signatures =
-    __transform_completion_signatures_t<_Sigs,
-                                        _ValueTransform,
-                                        _ErrorTransform,
-                                        _StoppedSigs,
-                                        __mtry_q<__concat_completion_signatures_t>::__f,
-                                        _MoreSigs>;
-
-  template <class _Sndr,
-            class _Env                                = env<>,
-            class _MoreSigs                           = completion_signatures<>,
-            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
-            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
-            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
-  using transform_completion_signatures_of =
-    transform_completion_signatures<completion_signatures_of_t<_Sndr, _Env>,
-                                    _MoreSigs,
-                                    _ValueTransform,
-                                    _ErrorTransform,
-                                    _StoppedSigs>;
-
+  using __gather_completion_signatures_t =                                //
+    __cmplsigs::__gather_sigs_fn<_WantedTag, __ok<_Sigs>>::template __f<  //
+      _Sigs,
+      _Then,
+      _Else,
+      _Variant,
+      _More...>;
+
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  // begin implementation of __transform_completion_signatures
   struct _IN_TRANSFORM_COMPLETION_SIGNATURES_;
   struct _A_TRANSFORM_FUNCTION_RETURNED_A_TYPE_THAT_IS_NOT_A_COMPLETION_SIGNATURES_SPECIALIZATION_;
   struct _COULD_NOT_CALL_THE_TRANSFORM_FUNCTION_WITH_THE_GIVEN_TEMPLATE_ARGUMENTS_;
@@ -344,7 +293,6 @@ namespace STDEXEC
     using __transform_expr_t =
       decltype(__cmplsigs::__transform_expr<_Args...>(__declval<_Fn const &>(), 0));
 
-    // transform_completion_signatures:
     template <class... _Args, class _Fn>
     [[nodiscard]]
     consteval auto __apply_transform(_Fn const &__fn)
@@ -402,17 +350,21 @@ namespace STDEXEC
       _StoppedFn __stopped_fn;
     };
 
+    template <class _ValueFn, class _ErrorFn, class _StoppedFn>
+    STDEXEC_HOST_DEVICE_DEDUCTION_GUIDE __transform_one(_ValueFn, _ErrorFn, _StoppedFn)
+      -> __transform_one<_ValueFn, _ErrorFn, _StoppedFn>;
+
     template <class _TransformOne>
     struct __transform_all_fn
     {
-      _TransformOne __tfx1;
-
       template <class... Sigs>
       [[nodiscard]]
       consteval auto operator()(Sigs *...sigs) const
       {
         return __concat_completion_signatures(__tfx1(sigs)...);
       }
+
+      _TransformOne __tfx1;
     };
 
     template <class _TransformOne>
@@ -420,6 +372,14 @@ namespace STDEXEC
       __transform_all_fn(_TransformOne) -> __transform_all_fn<_TransformOne>;
   }  // namespace __cmplsigs
 
+  //////////////////////////////////////////////////////////////////////////////////////////////////
+  //! Commonly needed transformations of completion signatures for use with
+  //! \c __transform_completion_signatures.
+  //!
+  //! * __keep_completion
+  //! * __ignore_completion
+  //! * __transform_arguments
+  //! * __decay_arguments
   template <class _SetTag>
   struct __keep_completion
   {
@@ -509,6 +469,101 @@ namespace STDEXEC
     }
   };
 
+  //! \brief Transforms completion signatures using provided transformation functions.
+  //!
+  //! This consteval function transforms a set of completion signatures by applying
+  //! custom transformation functions to value, error, and stopped completion cases.
+  //! The result can be augmented with additional extra signatures.
+  //!
+  //! \tparam _Completions The input completion signatures to transform.
+  //! \tparam _ValueFn     Function object that transforms set_value_t completions.
+  //!                      Defaults to __keep_completion<set_value_t>.
+  //! \tparam _ErrorFn     Function object that transforms set_error_t completions.
+  //!                      Defaults to __keep_completion<set_error_t>.
+  //! \tparam _StoppedFn   Function object that transforms set_stopped_t completions.
+  //!                      Defaults to __keep_completion<set_stopped_t>.
+  //! \tparam _ExtraSigs   Additional completion signatures to append to the result.
+  //!                      Defaults to an empty completion_signatures.
+  //!
+  //! \param __completions The input completion signatures object.
+  //! \param __value_fn    Value transformation function instance.
+  //! \param __error_fn    Error transformation function instance.
+  //! \param __stopped_fn  Stopped transformation function instance.
+  //! \param __extra_sigs  Extra signatures to append to the result.
+  //!
+  //! \return A transformed completion_signatures object combining the transformed
+  //!         input signatures with the extra signatures.
+  //!
+  //! \par Example
+  //!
+  //! The following example demonstrates how to use \c __transform_completion_signatures
+  //! to compute the completion signatures of the \c then sender.
+  //!
+  //! \code{.cpp}
+  //! namespace ex = STDEXEC;
+  //!
+  //! template <class Fn, class... Args>
+  //! consteval auto _transform_values()
+  //! {
+  //!   if constexpr (!std::invocable<Fn, Args...>)
+  //!   {
+  //!     // If Fn cannot be invoked with the given arguments, produce a compile-time
+  //!     // error.
+  //!     return ex::__throw_compile_time_error<
+  //!       _WHAT_(_FUNCTION_IS_NOT_CALLABLE_WITH_THE_GIVEN_ARGUMENTS_),
+  //!       _WHERE_(_IN_ALGORITHM_, then_t),
+  //!       _WITH_FUNCTION_(Fn),
+  //!       _WITH_ARGUMENTS_(Args...)>();
+  //!   }
+  //!   else
+  //!   {
+  //!     // transform the value types of the child sender into the value types of the
+  //!     // then sender by applying Fn to them.
+  //!     using result_t         = std::invoke_result_t<Fn, Args...>;
+  //!     constexpr bool is_void = std::is_void_v<result_t>;
+  //!     constexpr bool nothrow = std::is_nothrow_invocable_v<Fn, Args...>;
+  //!     if constexpr (is_void && nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t()>();
+  //!     }
+  //!     else if constexpr (is_void && !nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(),
+  //!                                        set_error_t(std::exception_ptr)>();
+  //!     }
+  //!     else if constexpr (!is_void && nothrow)
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(result_t)>();
+  //!     }
+  //!     else /* !is_void && !nothrow */
+  //!     {
+  //!       return ex::completion_signatures<set_value_t(result_t),
+  //!                                        set_error_t(std::exception_ptr)>();
+  //!     }
+  //!   }
+  //! }
+  //!
+  //! template <class Child, class Fn>
+  //! struct then_sender
+  //! {
+  //!   using sender_concept = ex::sender_t;
+  //!
+  //!   template <class Self, class... Env>
+  //!   static consteval auto get_completion_signatures()
+  //!   {
+  //!     // Compute the completion signatures of the child sender, and then transform
+  //!     // them into the completion signatures of the `then` sender.
+  //!     auto child_completions = ex::__get_child_completion_signatures<Self, Child, Env...>();
+  //!     auto value_fn = []<class... Args>() { return _transform_values<Fn, Args...>(); };
+  //!
+  //!     return ex::__transform_completion_signatures(child_completions, value_fn);
+  //!   }
+  //!
+  //!   // ...
+  //! };
+  //! \endcode
+  //!
+  //! \note This function is evaluated at compile-time (consteval).
   template <class _Completions,
             class _ValueFn   = __keep_completion<set_value_t>,
             class _ErrorFn   = __keep_completion<set_error_t>,
@@ -524,9 +579,7 @@ namespace STDEXEC
     {
       STDEXEC_COMPLSIGS_LET(__extra_sigs, _ExtraSigs{})
       {
-        __cmplsigs::__transform_one<_ValueFn, _ErrorFn, _StoppedFn> __tfx1{__value_fn,
-                                                                           __error_fn,
-                                                                           __stopped_fn};
+        __cmplsigs::__transform_one __tfx1{__value_fn, __error_fn, __stopped_fn};
         return __concat_completion_signatures(__completions.__apply(
                                                 __cmplsigs::__transform_all_fn(__tfx1)),
                                               __extra_sigs);
@@ -534,27 +587,10 @@ namespace STDEXEC
     }
   }
 
-  using __eptr_completion = completion_signatures<set_error_t(std::exception_ptr)>;
+  using __eptr_completion_t = completion_signatures<set_error_t(std::exception_ptr)>;
 
   template <class _NoExcept>
-  using __eptr_completion_unless_t = __if<_NoExcept, completion_signatures<>, __eptr_completion>;
-
-  template <bool _NoExcept>
-  using __eptr_completion_unless = __eptr_completion_unless_t<__mbool<_NoExcept>>;
-
-  template <class _Sender,
-            class _Env        = env<>,
-            class _More       = completion_signatures<>,
-            class _SetValue   = __qq<__cmplsigs::__default_set_value>,
-            class _SetError   = __qq<__cmplsigs::__default_set_error>,
-            class _SetStopped = completion_signatures<set_stopped_t()>>
-  using __try_make_completion_signatures =
-    __transform_completion_signatures_t<__completion_signatures_of_t<_Sender, _Env>,
-                                        _SetValue::template __f,
-                                        _SetError::template __f,
-                                        _SetStopped,
-                                        __mtry_q<__concat_completion_signatures_t>::__f,
-                                        _More>;
+  using __eptr_completion_unless_t = __if<_NoExcept, completion_signatures<>, __eptr_completion_t>;
 
   // The following utilities are needed fairly often:
   template <class _Fun, class... _Args>
@@ -570,7 +606,7 @@ namespace STDEXEC
            __mconst<__mbool<true>>::__f,
            __mand>,
          completion_signatures<>,
-         __eptr_completion>;
+         __eptr_completion_t>;
 
   template <class _Fun, class... _Args>
     requires __invocable<_Fun, _Args...>
@@ -584,4 +620,36 @@ namespace STDEXEC
   template <class _Completions>
   using __nothrow_decay_copyable_results_t =
     __cmplsigs::__partitions_of_t<_Completions>::__nothrow_decay_copyable::__all;
+
+#define STDEXEC_TRANSFORM_COMPLETION_SIGNATURES_DEPRECATION_MESSAGE \
+  "Please migrate to the exec::transform_completion_signatures API in <exec/completion_signatures.hpp>"
+
+  // Deprecated interfaces:
+  template <class _Sigs,
+            class _MoreSigs                           = completion_signatures<>,
+            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
+            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
+            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
+  using transform_completion_signatures
+    [[deprecated(STDEXEC_TRANSFORM_COMPLETION_SIGNATURES_DEPRECATION_MESSAGE)]] =
+      __transform_reduce_completion_signatures_t<_Sigs,
+                                                 _ValueTransform,
+                                                 _ErrorTransform,
+                                                 _StoppedSigs,
+                                                 __mtry_q<__concat_completion_signatures_t>::__f,
+                                                 _MoreSigs>;
+
+  template <class _Sndr,
+            class _Env                                = env<>,
+            class _MoreSigs                           = completion_signatures<>,
+            template <class...> class _ValueTransform = __cmplsigs::__default_set_value,
+            template <class...> class _ErrorTransform = __cmplsigs::__default_set_error,
+            class _StoppedSigs                        = completion_signatures<set_stopped_t()>>
+  using transform_completion_signatures_of
+    [[deprecated(STDEXEC_TRANSFORM_COMPLETION_SIGNATURES_DEPRECATION_MESSAGE)]] =
+      __transform_completion_signatures_t<completion_signatures_of_t<_Sndr, _Env>,
+                                          _MoreSigs,
+                                          _ValueTransform,
+                                          _ErrorTransform,
+                                          _StoppedSigs>;
 }  // namespace STDEXEC
diff --git a/include/stdexec/__detail/__upon_error.hpp b/include/stdexec/__detail/__upon_error.hpp
index b4fd6cb5b..e738a38d1 100644
--- a/include/stdexec/__detail/__upon_error.hpp
+++ b/include/stdexec/__detail/__upon_error.hpp
@@ -35,7 +35,7 @@ namespace STDEXEC
     using __on_not_callable = __mbind_front_q<__callable_error_t, upon_error_t>;
 
     template <class _Fun, class _CvSender, class... _Env>
-    using __completion_signatures_t = transform_completion_signatures<
+    using __completion_signatures_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<_CvSender, _Env...>,
       __with_error_invoke_t<__on_not_callable, set_error_t, _Fun, _CvSender, _Env...>,
       __cmplsigs::__default_set_value,
diff --git a/include/stdexec/__detail/__upon_stopped.hpp b/include/stdexec/__detail/__upon_stopped.hpp
index c781edd80..e496bb0b0 100644
--- a/include/stdexec/__detail/__upon_stopped.hpp
+++ b/include/stdexec/__detail/__upon_stopped.hpp
@@ -35,7 +35,7 @@ namespace STDEXEC
     using __on_not_callable = __mbind_front_q<__callable_error_t, upon_stopped_t>;
 
     template <class _Fun, class _CvSender, class... _Env>
-    using __completion_signatures_t = transform_completion_signatures<
+    using __completion_signatures_t = __transform_completion_signatures_t<
       __completion_signatures_of_t<_CvSender, _Env...>,
       __with_error_invoke_t<__on_not_callable, set_stopped_t, _Fun, _CvSender, _Env...>,
       __cmplsigs::__default_set_value,
diff --git a/include/stdexec/__detail/__when_all.hpp b/include/stdexec/__detail/__when_all.hpp
index a2134a000..97a8b13c6 100644
--- a/include/stdexec/__detail/__when_all.hpp
+++ b/include/stdexec/__detail/__when_all.hpp
@@ -170,8 +170,8 @@ namespace STDEXEC
     using __set_error_t = completion_signatures<set_error_t(__decay_t<_Error>)>;
 
     template <class _Sender, class... _Env>
-    using __nothrow_decay_copyable_results_t = __cmplsigs::__partitions_of_t<
-      __completion_signatures_of_t<_Sender, _Env...>>::__nothrow_decay_copyable::__all;
+    using __nothrow_decay_copyable_results_t =
+      STDEXEC::__nothrow_decay_copyable_results_t<__completion_signatures_of_t<_Sender, _Env...>>;
 
     template <class... _Env>
     struct __completions
@@ -203,11 +203,11 @@ namespace STDEXEC
         __concat_completion_signatures_t,
         __minvoke_q<__eptr_completion_unless_t, __all_nothrow_decay_copyable_results_t<_Senders...>>,
         __minvoke<__mwith_default<__qq<__set_values_sig_t>, completion_signatures<>>, _Senders...>,
-        __transform_completion_signatures_t<__completion_signatures_of_t<_Senders, _Env...>,
-                                            __mconst<completion_signatures<>>::__f,
-                                            __set_error_t,
-                                            completion_signatures<set_stopped_t()>,
-                                            __concat_completion_signatures_t>...>;
+        __transform_reduce_completion_signatures_t<__completion_signatures_of_t<_Senders, _Env...>,
+                                                   __mconst<completion_signatures<>>::__f,
+                                                   __set_error_t,
+                                                   completion_signatures<set_stopped_t()>,
+                                                   __concat_completion_signatures_t>...>;
     };
 
     template <class _Receiver, class _ValuesTuple>
diff --git a/test/nvexec/common.cuh b/test/nvexec/common.cuh
index 72a09cd2f..742c1503f 100644
--- a/test/nvexec/common.cuh
+++ b/test/nvexec/common.cuh
@@ -163,7 +163,7 @@ namespace
       using op_t = operation_state<STDEXEC::__copy_cvref_t<Self, Sender>, receiver<Receiver, Fun>>;
 
       template <class Self, class... Env>
-      using __completions_t = STDEXEC::transform_completion_signatures<
+      using __completions_t = STDEXEC::__transform_completion_signatures_t<
         STDEXEC::__completion_signatures_of_t<STDEXEC::__copy_cvref_t<Self, Sender>, Env...>,
         STDEXEC::completion_signatures<>,
         STDEXEC::__mbind_front_q<STDEXEC::__set_value_from_t, Fun>::template __f>;
diff --git a/test/stdexec/algos/adaptors/test_on3.cpp b/test/stdexec/algos/adaptors/test_on3.cpp
index c81129900..42fde0040 100644
--- a/test/stdexec/algos/adaptors/test_on3.cpp
+++ b/test/stdexec/algos/adaptors/test_on3.cpp
@@ -75,10 +75,11 @@ namespace
     template <ex::__decays_to<get_env_sender> Self, class Env>
     static consteval auto get_completion_signatures()
     {
-      return ex::__try_make_completion_signatures<ex::__copy_cvref_t<Self, Sndr>,
-                                                  Env,
-                                                  ex::completion_signatures<ex::set_value_t(Env)>,
-                                                  ex::__mconst<ex::completion_signatures<>>>{};
+      return ex::__transform_completion_signatures_of_t<
+        ex::__copy_cvref_t<Self, Sndr>,
+        Env,
+        ex::completion_signatures<ex::set_value_t(Env)>,
+        ex::__mconst<ex::completion_signatures<>>::__f>{};
     }
   };
 
diff --git a/test/stdexec/detail/test_completion_signatures.cpp b/test/stdexec/detail/test_completion_signatures.cpp
index 7c74ac713..13fe13d41 100644
--- a/test/stdexec/detail/test_completion_signatures.cpp
+++ b/test/stdexec/detail/test_completion_signatures.cpp
@@ -147,7 +147,8 @@ namespace
     static_assert(ex::__mset_eq<actual_t, expected_t>);
   }
 
-  TEST_CASE("transform_completion_signatures_of can replicate the completion signatures of input "
+  TEST_CASE("__transform_completion_signatures_of_t can replicate the completion signatures of "
+            "input "
             "senders",
             "[detail][completion_signatures]")
   {
@@ -157,11 +158,11 @@ namespace
     using snd_ec_t          = decltype(ex::just_error(error_code{}));
     using snd_stopped_t     = decltype(ex::just_stopped());
 
-    using cs_int         = ex::transform_completion_signatures_of<snd_int_t>;
-    using cs_double_char = ex::transform_completion_signatures_of<snd_double_char_t>;
-    using cs_eptr        = ex::transform_completion_signatures_of<snd_eptr_t>;
-    using cs_ec          = ex::transform_completion_signatures_of<snd_ec_t>;
-    using cs_stopped     = ex::transform_completion_signatures_of<snd_stopped_t>;
+    using cs_int         = ex::__transform_completion_signatures_of_t<snd_int_t>;
+    using cs_double_char = ex::__transform_completion_signatures_of_t<snd_double_char_t>;
+    using cs_eptr        = ex::__transform_completion_signatures_of_t<snd_eptr_t>;
+    using cs_ec          = ex::__transform_completion_signatures_of_t<snd_ec_t>;
+    using cs_stopped     = ex::__transform_completion_signatures_of_t<snd_stopped_t>;
 
     expect_val_types<cs_int, ex::__mlist<int>>();
     expect_val_types<cs_double_char, ex::__mlist<double, char>>();
@@ -176,7 +177,7 @@ namespace
     expect_err_types<cs_stopped>();
   }
 
-  TEST_CASE("transform_completion_signatures_of with ex::env<> can replicate the completion "
+  TEST_CASE("__transform_completion_signatures_of_t with ex::env<> can replicate the completion "
             "signatures of "
             "input "
             "senders",
@@ -188,11 +189,11 @@ namespace
     using snd_ec_t          = decltype(ex::just_error(error_code{}));
     using snd_stopped_t     = decltype(ex::just_stopped());
 
-    using cs_int         = ex::transform_completion_signatures_of<snd_int_t, ex::env<>>;
-    using cs_double_char = ex::transform_completion_signatures_of<snd_double_char_t, ex::env<>>;
-    using cs_eptr        = ex::transform_completion_signatures_of<snd_eptr_t, ex::env<>>;
-    using cs_ec          = ex::transform_completion_signatures_of<snd_ec_t, ex::env<>>;
-    using cs_stopped     = ex::transform_completion_signatures_of<snd_stopped_t, ex::env<>>;
+    using cs_int         = ex::__transform_completion_signatures_of_t<snd_int_t, ex::env<>>;
+    using cs_double_char = ex::__transform_completion_signatures_of_t<snd_double_char_t, ex::env<>>;
+    using cs_eptr        = ex::__transform_completion_signatures_of_t<snd_eptr_t, ex::env<>>;
+    using cs_ec          = ex::__transform_completion_signatures_of_t<snd_ec_t, ex::env<>>;
+    using cs_stopped     = ex::__transform_completion_signatures_of_t<snd_stopped_t, ex::env<>>;
 
     expect_val_types<cs_int, ex::__mlist<int>>();
     expect_val_types<cs_double_char, ex::__mlist<double, char>>();
@@ -207,11 +208,11 @@ namespace
     expect_err_types<cs_stopped>();
   }
 
-  TEST_CASE("transform_completion_signatures_of can add other error signatures",
+  TEST_CASE("__transform_completion_signatures_of_t can add other error signatures",
             "[detail][completion_signatures]")
   {
     using snd_double_t = decltype(ex::just_error(std::exception_ptr{}));
-    using cs_with_ec   = ex::transform_completion_signatures_of<
+    using cs_with_ec   = ex::__transform_completion_signatures_of_t<
         snd_double_t,
         ex::env<>,
         ex::completion_signatures<ex::set_error_t(error_code)>>;
@@ -220,12 +221,12 @@ namespace
     expect_err_types<cs_with_ec, error_code, exception_ptr>();
   }
 
-  TEST_CASE("transform_completion_signatures_of can add other error signatures, but will dedup "
+  TEST_CASE("__transform_completion_signatures_of_t can add other error signatures, but will dedup "
             "them",
             "[detail][completion_signatures]")
   {
     using snd_double_t = decltype(ex::just(3.14));
-    using cs_with_ec   = ex::transform_completion_signatures_of<
+    using cs_with_ec   = ex::__transform_completion_signatures_of_t<
         snd_double_t,
         ex::env<>,
         ex::completion_signatures<ex::set_error_t(exception_ptr)>>;
@@ -234,11 +235,11 @@ namespace
     expect_err_types<cs_with_ec, exception_ptr>();
   }
 
-  TEST_CASE("transform_completion_signatures_of can add other value signatures",
+  TEST_CASE("__transform_completion_signatures_of_t can add other value signatures",
             "[detail][completion_signatures]")
   {
     using snd_double_t = decltype(ex::just(3.14));
-    using cs           = ex::transform_completion_signatures_of<
+    using cs           = ex::__transform_completion_signatures_of_t<
                 snd_double_t,
                 ex::env<>,
                 ex::completion_signatures<ex::set_value_t(int), ex::set_value_t(double)>>;
@@ -253,11 +254,11 @@ namespace
   template <class Err>
   using optional_set_error_sig = ex::completion_signatures<ex::set_error_t(optional<Err>)>;
 
-  TEST_CASE("transform_completion_signatures_of can transform value types signatures",
+  TEST_CASE("__transform_completion_signatures_of_t can transform value types signatures",
             "[detail][completion_signatures]")
   {
     using snd_double_t = decltype(ex::just(3.14));
-    using cs           = ex::transform_completion_signatures_of<
+    using cs           = ex::__transform_completion_signatures_of_t<
                 snd_double_t,
                 ex::env<>,
                 ex::completion_signatures<ex::set_value_t(int), ex::set_value_t(double)>,
@@ -268,16 +269,16 @@ namespace
     expect_val_types<cs, ex::__mlist<int>, ex::__mlist<double>, ex::__mlist<string, double>>();
   }
 
-  TEST_CASE("transform_completion_signatures_of can transform error types signatures",
+  TEST_CASE("__transform_completion_signatures_of_t can transform error types signatures",
             "[detail][completion_signatures]")
   {
     using snd_eptr_t = decltype(ex::just_error(std::exception_ptr{}));
-    using cs =
-      ex::transform_completion_signatures_of<snd_eptr_t,
-                                             ex::env<>,
-                                             ex::completion_signatures<ex::set_error_t(error_code)>,
-                                             ex::__cmplsigs::__default_set_value,
-                                             optional_set_error_sig>;
+    using cs         = ex::__transform_completion_signatures_of_t<
+              snd_eptr_t,
+              ex::env<>,
+              ex::completion_signatures<ex::set_error_t(error_code)>,
+              ex::__cmplsigs::__default_set_value,
+              optional_set_error_sig>;
 
     // will transform the original "exception_ptr" into optional<exception_ptr>
     // then will add the other "error_code" as specified in the additional signatures