diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 778c6d4..47e152c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,17 +20,24 @@ jobs:
     name: ${{ matrix.os }}/llvm${{ matrix.llvm }}/py${{ matrix.py }}/c++${{ matrix.cxx }}${{ matrix.vg && '/vg' || '' }}${{ matrix.flavor == 'cling' && '/cling' || '' }}
     strategy:
       fail-fast: false
-      # Mirrors CppInterOp's cppyy PR cells: clang-repl on the same OS/arch/LLVM
-      # /valgrind combos at Python 3.14, plus a cling cell and a C++23 cell
-      # (test_cpp23features runs only there). Breadth (3.12/3.13, C++17, LLVM
-      # 20, arm) lives in nightly.
+      # Every supported Python against both supported LLVM majors on ubuntu;
+      # every supported Python on macOS, alternating the LLVM major; a C++23
+      # cell (test_cpp23features runs only there) and a cling cell. Remaining
+      # breadth (C++17, LLVM 20, arm) lives in nightly.
       matrix:
         include:
           - { os: ubuntu-24.04,   llvm: '21', flavor: system, py: '3.14', cxx: '20', vg: true }
+          - { os: ubuntu-24.04,   llvm: '21', flavor: system, py: '3.13', cxx: '20' }
+          - { os: ubuntu-24.04,   llvm: '21', flavor: system, py: '3.12', cxx: '20' }
           - { os: ubuntu-24.04,   llvm: '22', flavor: '',     py: '3.14', cxx: '20' }
           - { os: ubuntu-24.04,   llvm: '22', flavor: '',     py: '3.14', cxx: '23' }
+          - { os: ubuntu-24.04,   llvm: '22', flavor: '',     py: '3.13', cxx: '20' }
+          - { os: ubuntu-24.04,   llvm: '22', flavor: '',     py: '3.12', cxx: '20' }
           - { os: macos-26,       llvm: '21', flavor: system, py: '3.14', cxx: '20' }
+          - { os: macos-26,       llvm: '22', flavor: '',     py: '3.13', cxx: '20' }
+          - { os: macos-26,       llvm: '21', flavor: system, py: '3.12', cxx: '20' }
           - { os: macos-26-intel, llvm: '21', flavor: system, py: '3.14', cxx: '20' }
+          - { os: macos-26-intel, llvm: '22', flavor: '',     py: '3.12', cxx: '20' }
           # cling backend, against the cached llvm-root (cling-llvm22) recipe cell.
           - { os: ubuntu-24.04,   llvm: '22', flavor: cling,  flavor_version: cling-llvm22, py: '3.14', cxx: '20' }
     uses: compiler-research/ci-workflows/.github/workflows/cppjit.yml@main
diff --git a/.github/workflows/nightly.yml b/.github/workflows/nightly.yml
index 020d612..db0df44 100644
--- a/.github/workflows/nightly.yml
+++ b/.github/workflows/nightly.yml
@@ -22,8 +22,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        # Superset of the PR matrix + breadth (py 3.12/3.13, C++17/23, LLVM 20,
-        # arm) and one cling cell. valgrind only where a supp is vendored: the
+        # Breadth beyond the PR matrix (C++17, LLVM 20, arm) and one cling
+        # cell. valgrind only where a supp is vendored: the
         # LLVM 21 cells (clang21) and the arm LLVM 22 cell (clang22), both under
         # .github/valgrind/.
         include: