diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index 9679c5002..eab3e1c0d 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -605,7 +605,7 @@ struct instance {
     bool simple_instance_registered : 1;
     /// If true, get_internals().patients has an entry for this object
     bool has_patients : 1;
-// Cannot use PYBIND11_INTERNALS_VERSION >= 6 here without refactoring.
+// Cannot use PYBIND11_INTERNALS_VERSION >= 106 here without refactoring.
 #if PYBIND11_VERSION_MAJOR >= 3
     /// If true, this Python object needs to be kept alive for the lifetime of the C++ value.
     bool is_alias : 1;
diff --git a/include/pybind11/detail/internals.h b/include/pybind11/detail/internals.h
index 1bbd0e327..892e611d6 100644
--- a/include/pybind11/detail/internals.h
+++ b/include/pybind11/detail/internals.h
@@ -38,23 +38,17 @@
 /// changed to the new version.
 #ifndef PYBIND11_INTERNALS_VERSION
 #    if PYBIND11_VERSION_MAJOR >= 3
-#        define PYBIND11_INTERNALS_VERSION 6
-#    elif PY_VERSION_HEX >= 0x030C0000 || defined(_MSC_VER)
-// Version bump for Python 3.12+, before first 3.12 beta release.
-// Version bump for MSVC piggy-backed on PR #4779. See comments there.
-#        ifdef Py_GIL_DISABLED
-#            define PYBIND11_INTERNALS_VERSION 6
-#        else
-#            define PYBIND11_INTERNALS_VERSION 5
-#        endif
+#        define PYBIND11_INTERNALS_VERSION 106
 #    else
-#        define PYBIND11_INTERNALS_VERSION 4
+#        define PYBIND11_INTERNALS_VERSION 6
 #    endif
 #endif
 
 // This requirement is mainly to reduce the support burden (see PR #4570).
 static_assert(PY_VERSION_HEX < 0x030C0000 || PYBIND11_INTERNALS_VERSION >= 5,
               "pybind11 ABI version 5 is the minimum for Python 3.12+");
+static_assert(PYBIND11_INTERNALS_VERSION >= 4,
+              "pybind11 ABI version 4 is the minimum for all platforms.");
 
 PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
@@ -244,7 +238,7 @@ struct internals {
     }
 };
 
-#if PYBIND11_INTERNALS_VERSION >= 6
+#if PYBIND11_INTERNALS_VERSION >= 106
 
 #    define PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
 
diff --git a/include/pybind11/eigen/matrix.h b/include/pybind11/eigen/matrix.h
index 5cf1f0a2a..d2999d61b 100644
--- a/include/pybind11/eigen/matrix.h
+++ b/include/pybind11/eigen/matrix.h
@@ -316,8 +316,11 @@ struct type_caster<Type, enable_if_t<is_eigen_dense_plain<Type>::value>> {
             return false;
         }
 
+        PYBIND11_WARNING_PUSH
+        PYBIND11_WARNING_DISABLE_GCC("-Wmaybe-uninitialized") // See PR #5516
         // Allocate the new type, then build a numpy reference into it
         value = Type(fits.rows, fits.cols);
+        PYBIND11_WARNING_POP
         auto ref = reinterpret_steal<array>(eigen_ref_array<props>(value));
         if (dims == 1) {
             ref = ref.squeeze();