diff --git a/Cargo.toml b/Cargo.toml
index 5386b76f573..78ab72525a5 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -69,6 +69,9 @@ default = ["macros"]
 # and IntoPy traits
 experimental-inspect = []
 
+# Enables annotating Rust inline modules with #[pymodule] to build Python modules declaratively
+experimental-declarative-modules = ["pyo3-macros/experimental-declarative-modules"]
+
 # Enables macros: #[pyclass], #[pymodule], #[pyfunction] etc.
 macros = ["pyo3-macros", "indoc", "unindent"]
 
diff --git a/newsfragments/3815.added.md b/newsfragments/3815.added.md
index dd450ca88c6..e4fd3e9315a 100644
--- a/newsfragments/3815.added.md
+++ b/newsfragments/3815.added.md
@@ -1 +1,2 @@
-The ability to create Python modules with a Rust `mod` block.
\ No newline at end of file
+The ability to create Python modules with a Rust `mod` block
+behind the `experimental-declarative-modules` feature.
\ No newline at end of file
diff --git a/pyo3-macros/Cargo.toml b/pyo3-macros/Cargo.toml
index 576c94a2bc1..a0368a5f364 100644
--- a/pyo3-macros/Cargo.toml
+++ b/pyo3-macros/Cargo.toml
@@ -15,6 +15,7 @@ proc-macro = true
 
 [features]
 multiple-pymethods = []
+experimental-declarative-modules = []
 
 [dependencies]
 proc-macro2 = { version = "1", default-features = false }
diff --git a/pyo3-macros/src/lib.rs b/pyo3-macros/src/lib.rs
index 8dbf2782d5b..098b23e709f 100644
--- a/pyo3-macros/src/lib.rs
+++ b/pyo3-macros/src/lib.rs
@@ -37,7 +37,7 @@ use syn::{parse::Nothing, parse_macro_input, Item};
 pub fn pymodule(args: TokenStream, input: TokenStream) -> TokenStream {
     parse_macro_input!(args as Nothing);
     match parse_macro_input!(input as Item) {
-        Item::Mod(module) => pymodule_module_impl(module),
+        Item::Mod(module) if cfg!(feature = "experimental-declarative-modules") => pymodule_module_impl(module),
         Item::Fn(function) => pymodule_function_impl(function),
         unsupported => Err(syn::Error::new_spanned(
             unsupported,
diff --git a/pytests/src/lib.rs b/pytests/src/lib.rs
index a5ee6b20b7b..85cf435d1d9 100644
--- a/pytests/src/lib.rs
+++ b/pytests/src/lib.rs
@@ -1,4 +1,6 @@
 use pyo3::prelude::*;
+use pyo3::types::PyDict;
+use pyo3::wrap_pymodule;
 
 pub mod awaitable;
 pub mod buf_and_str;
@@ -16,39 +18,43 @@ pub mod sequence;
 pub mod subclassing;
 
 #[pymodule]
-mod pyo3_pytests {
-    use super::*;
-    use pyo3::types::PyDict;
-    #[pymodule_export]
-    use {
-        awaitable::awaitable, comparisons::comparisons, dict_iter::dict_iter, enums::enums,
-        misc::misc, objstore::objstore, othermod::othermod, path::path, pyclasses::pyclasses,
-        pyfunctions::pyfunctions, sequence::sequence, subclassing::subclassing,
-    };
+fn pyo3_pytests(py: Python<'_>, m: &PyModule) -> PyResult<()> {
+    m.add_wrapped(wrap_pymodule!(awaitable::awaitable))?;
     #[cfg(not(Py_LIMITED_API))]
-    #[pymodule_export]
-    use {buf_and_str::buf_and_str, datetime::datetime};
+    m.add_wrapped(wrap_pymodule!(buf_and_str::buf_and_str))?;
+    m.add_wrapped(wrap_pymodule!(comparisons::comparisons))?;
+    #[cfg(not(Py_LIMITED_API))]
+    m.add_wrapped(wrap_pymodule!(datetime::datetime))?;
+    m.add_wrapped(wrap_pymodule!(dict_iter::dict_iter))?;
+    m.add_wrapped(wrap_pymodule!(enums::enums))?;
+    m.add_wrapped(wrap_pymodule!(misc::misc))?;
+    m.add_wrapped(wrap_pymodule!(objstore::objstore))?;
+    m.add_wrapped(wrap_pymodule!(othermod::othermod))?;
+    m.add_wrapped(wrap_pymodule!(path::path))?;
+    m.add_wrapped(wrap_pymodule!(pyclasses::pyclasses))?;
+    m.add_wrapped(wrap_pymodule!(pyfunctions::pyfunctions))?;
+    m.add_wrapped(wrap_pymodule!(sequence::sequence))?;
+    m.add_wrapped(wrap_pymodule!(subclassing::subclassing))?;
+
+    // Inserting to sys.modules allows importing submodules nicely from Python
+    // e.g. import pyo3_pytests.buf_and_str as bas
+
+    let sys = PyModule::import(py, "sys")?;
+    let sys_modules: &PyDict = sys.getattr("modules")?.downcast()?;
+    sys_modules.set_item("pyo3_pytests.awaitable", m.getattr("awaitable")?)?;
+    sys_modules.set_item("pyo3_pytests.buf_and_str", m.getattr("buf_and_str")?)?;
+    sys_modules.set_item("pyo3_pytests.comparisons", m.getattr("comparisons")?)?;
+    sys_modules.set_item("pyo3_pytests.datetime", m.getattr("datetime")?)?;
+    sys_modules.set_item("pyo3_pytests.dict_iter", m.getattr("dict_iter")?)?;
+    sys_modules.set_item("pyo3_pytests.enums", m.getattr("enums")?)?;
+    sys_modules.set_item("pyo3_pytests.misc", m.getattr("misc")?)?;
+    sys_modules.set_item("pyo3_pytests.objstore", m.getattr("objstore")?)?;
+    sys_modules.set_item("pyo3_pytests.othermod", m.getattr("othermod")?)?;
+    sys_modules.set_item("pyo3_pytests.path", m.getattr("path")?)?;
+    sys_modules.set_item("pyo3_pytests.pyclasses", m.getattr("pyclasses")?)?;
+    sys_modules.set_item("pyo3_pytests.pyfunctions", m.getattr("pyfunctions")?)?;
+    sys_modules.set_item("pyo3_pytests.sequence", m.getattr("sequence")?)?;
+    sys_modules.set_item("pyo3_pytests.subclassing", m.getattr("subclassing")?)?;
 
-    #[pymodule_init]
-    fn init(m: &Bound<'_, PyModule>) -> PyResult<()> {
-        // Inserting to sys.modules allows importing submodules nicely from Python
-        // e.g. import pyo3_pytests.buf_and_str as bas
-        let sys = PyModule::import(m.py(), "sys")?;
-        let sys_modules: &PyDict = sys.getattr("modules")?.downcast()?;
-        sys_modules.set_item("pyo3_pytests.awaitable", m.getattr("awaitable")?)?;
-        sys_modules.set_item("pyo3_pytests.buf_and_str", m.getattr("buf_and_str")?)?;
-        sys_modules.set_item("pyo3_pytests.comparisons", m.getattr("comparisons")?)?;
-        sys_modules.set_item("pyo3_pytests.datetime", m.getattr("datetime")?)?;
-        sys_modules.set_item("pyo3_pytests.dict_iter", m.getattr("dict_iter")?)?;
-        sys_modules.set_item("pyo3_pytests.enums", m.getattr("enums")?)?;
-        sys_modules.set_item("pyo3_pytests.misc", m.getattr("misc")?)?;
-        sys_modules.set_item("pyo3_pytests.objstore", m.getattr("objstore")?)?;
-        sys_modules.set_item("pyo3_pytests.othermod", m.getattr("othermod")?)?;
-        sys_modules.set_item("pyo3_pytests.path", m.getattr("path")?)?;
-        sys_modules.set_item("pyo3_pytests.pyclasses", m.getattr("pyclasses")?)?;
-        sys_modules.set_item("pyo3_pytests.pyfunctions", m.getattr("pyfunctions")?)?;
-        sys_modules.set_item("pyo3_pytests.sequence", m.getattr("sequence")?)?;
-        sys_modules.set_item("pyo3_pytests.subclassing", m.getattr("subclassing")?)?;
-        Ok(())
-    }
-}
+    Ok(())
+}
\ No newline at end of file
diff --git a/tests/test_append_to_inittab.rs b/tests/test_append_to_inittab.rs
index 06ecc0ef893..eb812433585 100644
--- a/tests/test_append_to_inittab.rs
+++ b/tests/test_append_to_inittab.rs
@@ -13,6 +13,7 @@ fn module_fn_with_functions(_py: Python<'_>, m: &PyModule) -> PyResult<()> {
     Ok(())
 }
 
+#[cfg(feature = "experimental-declarative-modules")]
 #[pymodule]
 mod module_mod_with_functions {
     #[pymodule_export]
@@ -24,7 +25,6 @@ mod module_mod_with_functions {
 fn test_module_append_to_inittab() {
     use pyo3::append_to_inittab;
     append_to_inittab!(module_fn_with_functions);
-    append_to_inittab!(module_mod_with_functions);
     Python::with_gil(|py| {
         py.run_bound(
             r#"
@@ -37,6 +37,10 @@ assert module_fn_with_functions.foo() == 123
         .map_err(|e| e.display(py))
         .unwrap();
     });
+
+    #[cfg(feature = "experimental-declarative-modules")]
+    append_to_inittab!(module_mod_with_functions);
+    #[cfg(feature = "experimental-declarative-modules")]
     Python::with_gil(|py| {
         py.run_bound(
             r#"
diff --git a/tests/test_module.rs b/tests/test_module.rs
index 6944fd1318e..31e7c1f0a53 100644
--- a/tests/test_module.rs
+++ b/tests/test_module.rs
@@ -494,6 +494,7 @@ create_exception!(
 );
 
 /// A module written using declarative syntax.
+#[cfg(feature = "experimental-declarative-modules")]
 #[pymodule]
 mod declarative_module {
     #[pymodule_export]
@@ -512,11 +513,13 @@ mod declarative_module {
     }
 }
 
+#[cfg(feature = "experimental-declarative-modules")]
 #[pyfunction]
 fn double_value(v: &ValueClass) -> usize {
     v.value * 2
 }
 
+#[cfg(feature = "experimental-declarative-modules")]
 #[pymodule]
 mod declarative_submodule {
     #[pymodule_export]
@@ -524,6 +527,7 @@ mod declarative_submodule {
 }
 
 /// A module written using declarative syntax.
+#[cfg(feature = "experimental-declarative-modules")]
 #[pymodule]
 #[pyo3(name = "declarative_module_renamed")]
 mod declarative_module2 {
@@ -531,6 +535,7 @@ mod declarative_module2 {
     use super::double;
 }
 
+#[cfg(feature = "experimental-declarative-modules")]
 #[test]
 fn test_declarative_module() {
     Python::with_gil(|py| {