diff --git a/stl/inc/algorithm b/stl/inc/algorithm
index 81fef0ff11..ee01e63b13 100644
--- a/stl/inc/algorithm
+++ b/stl/inc/algorithm
@@ -90,7 +90,7 @@ struct _Optimistic_temporary_buffer { // temporary storage with _alloca-like att
 
     _Ty* _Data; // points to heap memory iff _Capacity > _Optimistic_count
     ptrdiff_t _Capacity;
-    aligned_union_t<0, _Ty> _Stack_space[_Optimistic_count];
+    _Aligned_storage_t<sizeof(_Ty), alignof(_Ty)> _Stack_space[_Optimistic_count];
 };
 
 #ifdef __cpp_lib_concepts
diff --git a/stl/inc/condition_variable b/stl/inc/condition_variable
index 20b6635d43..10c0088aa8 100644
--- a/stl/inc/condition_variable
+++ b/stl/inc/condition_variable
@@ -248,7 +248,7 @@ public:
 private:
     shared_ptr<mutex> _Myptr;
 
-    aligned_storage_t<_Cnd_internal_imp_size, _Cnd_internal_imp_alignment> _Cnd_storage;
+    _Aligned_storage_t<_Cnd_internal_imp_size, _Cnd_internal_imp_alignment> _Cnd_storage;
 
     _NODISCARD _Cnd_t _Mycnd() noexcept { // get pointer to _Cnd_internal_imp_t inside _Cnd_storage
         return reinterpret_cast<_Cnd_t>(&_Cnd_storage);
diff --git a/stl/inc/mutex b/stl/inc/mutex
index 0d8ac1b781..be82a1fbaa 100644
--- a/stl/inc/mutex
+++ b/stl/inc/mutex
@@ -76,7 +76,7 @@ private:
     friend condition_variable;
     friend condition_variable_any;
 
-    aligned_storage_t<_Mtx_internal_imp_size, _Mtx_internal_imp_alignment> _Mtx_storage;
+    _Aligned_storage_t<_Mtx_internal_imp_size, _Mtx_internal_imp_alignment> _Mtx_storage;
 
     _Mtx_t _Mymtx() noexcept { // get pointer to _Mtx_internal_imp_t inside _Mtx_storage
         return reinterpret_cast<_Mtx_t>(&_Mtx_storage);
@@ -698,7 +698,7 @@ public:
     }
 
 private:
-    aligned_storage_t<_Cnd_internal_imp_size, _Cnd_internal_imp_alignment> _Cnd_storage;
+    _Aligned_storage_t<_Cnd_internal_imp_size, _Cnd_internal_imp_alignment> _Cnd_storage;
 
     _Cnd_t _Mycnd() noexcept { // get pointer to _Cnd_internal_imp_t inside _Cnd_storage
         return reinterpret_cast<_Cnd_t>(&_Cnd_storage);
diff --git a/stl/inc/type_traits b/stl/inc/type_traits
index 4c3c71fc39..8ac768676b 100644
--- a/stl/inc/type_traits
+++ b/stl/inc/type_traits
@@ -1055,15 +1055,24 @@ struct _Aligned<_Len, _Align, char, false> {
     using type                  = typename _Aligned<_Len, _Align, _Next, _Fits>::type;
 };
 
+// TRANSITION, ABI: Internal non-deprecated version to avoid ABI changes due to deprecation
 template <size_t _Len, size_t _Align = alignof(max_align_t)>
-struct aligned_storage { // define type with size _Len and alignment _Align
+struct _Aligned_storage { // define type with size _Len and alignment _Align
     using _Next                 = char;
     static constexpr bool _Fits = _Align <= alignof(_Next);
     using type                  = typename _Aligned<_Len, _Align, _Next, _Fits>::type;
 };
 
 template <size_t _Len, size_t _Align = alignof(max_align_t)>
-using aligned_storage_t = typename aligned_storage<_Len, _Align>::type;
+using _Aligned_storage_t = typename _Aligned_storage<_Len, _Align>::type;
+
+template <size_t _Len, size_t _Align = alignof(max_align_t)>
+struct _CXX23_DEPRECATE_ALIGNED_STORAGE aligned_storage { // define type with size _Len and alignment _Align
+    using type = _Aligned_storage_t<_Len, _Align>;
+};
+
+template <size_t _Len, size_t _Align = alignof(max_align_t)>
+using aligned_storage_t _CXX23_DEPRECATE_ALIGNED_STORAGE = _Aligned_storage_t<_Len, _Align>;
 
 template <size_t... _Vals>
 struct _Maximum;
@@ -1080,15 +1089,18 @@ struct _Maximum<_First, _Second, _Rest...> : _Maximum<(_First < _Second ? _Secon
 };
 
 template <size_t _Len, class... _Types>
-struct aligned_union { // define type with size at least _Len, for storing anything in _Types
+struct _CXX23_DEPRECATE_ALIGNED_UNION aligned_union {
+    // define type with size at least _Len, for storing anything in _Types
     static constexpr size_t _Max_len        = _Maximum<_Len, sizeof(_Types)...>::value; // NOT sizeof...(_Types)
     static constexpr size_t alignment_value = _Maximum<alignof(_Types)...>::value;
 
-    using type = aligned_storage_t<_Max_len, alignment_value>;
+    using type = _Aligned_storage_t<_Max_len, alignment_value>;
 };
 
+_STL_DISABLE_DEPRECATED_WARNING
 template <size_t _Len, class... _Types>
-using aligned_union_t = typename aligned_union<_Len, _Types...>::type;
+using aligned_union_t _CXX23_DEPRECATE_ALIGNED_UNION = typename aligned_union<_Len, _Types...>::type;
+_STL_RESTORE_DEPRECATED_WARNING
 
 template <class _Ty, bool = is_enum_v<_Ty>>
 struct _Underlying_type {
diff --git a/stl/inc/xnode_handle.h b/stl/inc/xnode_handle.h
index 077aa77d7e..e6e7627bbe 100644
--- a/stl/inc/xnode_handle.h
+++ b/stl/inc/xnode_handle.h
@@ -75,7 +75,8 @@ class _Node_handle : public _Base<_Node_handle<_Node, _Alloc, _Base, _Types...>,
     using _Nodeptr       = typename _Alnode_traits::pointer;
 
     _Nodeptr _Ptr{};
-    aligned_union_t<0, _Alloc> _Alloc_storage; // Invariant: contains a live _Alloc iff _Ptr != nullptr
+    _Aligned_storage_t<sizeof(_Alloc), alignof(_Alloc)>
+        _Alloc_storage; // Invariant: contains a live _Alloc iff _Ptr != nullptr
 
     void _Clear() noexcept { // destroy any contained node and return to the empty state
         if (_Ptr != nullptr) {
diff --git a/stl/inc/yvals_core.h b/stl/inc/yvals_core.h
index 3961c40de9..88c06ebb29 100644
--- a/stl/inc/yvals_core.h
+++ b/stl/inc/yvals_core.h
@@ -291,6 +291,7 @@
 // P1132R7 out_ptr(), inout_ptr()
 // P1147R1 Printing volatile Pointers
 // P1272R4 byteswap()
+// P1413R3 Deprecate aligned_storage And aligned_union
 // P1425R4 Iterator Pair Constructors For stack And queue
 // P1659R3 ranges::starts_with, ranges::ends_with
 // P1679R3 contains() For basic_string/basic_string_view
@@ -1144,7 +1145,31 @@
 #define _CXX20_DEPRECATE_IS_ALWAYS_EQUAL
 #endif // ^^^ warning disabled ^^^
 
-// next warning number: STL4034
+#if _HAS_CXX23 && !defined(_SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING) \
+    && !defined(_SILENCE_ALL_CXX23_DEPRECATION_WARNINGS)
+#define _CXX23_DEPRECATE_ALIGNED_STORAGE                                                     \
+    [[deprecated("warning STL4034: "                                                         \
+                 "std::aligned_storage and std::aligned_storage_t are deprecated in C++23. " \
+                 "Prefer alignas(T) std::byte t_buff[sizeof(T)]. "                           \
+                 "You can define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING "        \
+                 "or _SILENCE_ALL_CXX23_DEPRECATION_WARNINGS to acknowledge that you have received this warning.")]]
+#else // ^^^ warning enabled / warning disabled vvv
+#define _CXX23_DEPRECATE_ALIGNED_STORAGE
+#endif // ^^^ warning disabled ^^^
+
+#if _HAS_CXX23 && !defined(_SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING) \
+    && !defined(_SILENCE_ALL_CXX23_DEPRECATION_WARNINGS)
+#define _CXX23_DEPRECATE_ALIGNED_UNION                                                   \
+    [[deprecated("warning STL4035: "                                                     \
+                 "std::aligned_union and std::aligned_union_t are deprecated in C++23. " \
+                 "Prefer alignas(Ts...) std::byte t_buff[std::max({sizeof(Ts)...})]. "   \
+                 "You can define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING "      \
+                 "or _SILENCE_ALL_CXX23_DEPRECATION_WARNINGS to acknowledge that you have received this warning.")]]
+#else // ^^^ warning enabled / warning disabled vvv
+#define _CXX23_DEPRECATE_ALIGNED_UNION
+#endif // ^^^ warning disabled ^^^
+
+// next warning number: STL4036
 
 // P0619R4 Removing C++17-Deprecated Features
 #ifndef _HAS_FEATURES_REMOVED_IN_CXX20
diff --git a/stl/src/cond.cpp b/stl/src/cond.cpp
index 350bb5c60e..46d82ae113 100644
--- a/stl/src/cond.cpp
+++ b/stl/src/cond.cpp
@@ -12,9 +12,8 @@
 #include "primitives.hpp"
 
 struct _Cnd_internal_imp_t { // condition variable implementation for ConcRT
-    std::aligned_storage_t<Concurrency::details::stl_condition_variable_max_size,
-        Concurrency::details::stl_condition_variable_max_alignment>
-        cv;
+    typename std::_Aligned_storage<Concurrency::details::stl_condition_variable_max_size,
+        Concurrency::details::stl_condition_variable_max_alignment>::type cv;
 
     [[nodiscard]] Concurrency::details::stl_condition_variable_interface* _get_cv() noexcept {
         // get pointer to implementation
diff --git a/stl/src/mutex.cpp b/stl/src/mutex.cpp
index 5db8385bec..fcf0efcd19 100644
--- a/stl/src/mutex.cpp
+++ b/stl/src/mutex.cpp
@@ -40,9 +40,8 @@ extern "C" _CRTIMP2 void __cdecl __set_stl_sync_api_mode(__stl_sync_api_modes_en
 
 struct _Mtx_internal_imp_t { // ConcRT mutex
     int type;
-    std::aligned_storage_t<Concurrency::details::stl_critical_section_max_size,
-        Concurrency::details::stl_critical_section_max_alignment>
-        cs;
+    typename std::_Aligned_storage<Concurrency::details::stl_critical_section_max_size,
+        Concurrency::details::stl_critical_section_max_alignment>::type cs;
     long thread_id;
     int count;
     Concurrency::details::stl_critical_section_interface* _get_cs() { // get pointer to implementation
diff --git a/tests/libcxx/expected_results.txt b/tests/libcxx/expected_results.txt
index 8ccf16fbfe..60a5168d86 100644
--- a/tests/libcxx/expected_results.txt
+++ b/tests/libcxx/expected_results.txt
@@ -221,11 +221,11 @@ std/containers/unord/unord.set/max_size.pass.cpp FAIL
 std/utilities/tuple/tuple.tuple/tuple.apply/apply_large_arity.pass.cpp SKIPPED
 std/utilities/tuple/tuple.tuple/tuple.cnstr/recursion_depth.pass.cpp SKIPPED
 
-# Deprecation is a mess. We disable all deprecations in msvc_stdlib_force_include.h to allow libc++ tests for
-# deprecated features to pass, which breaks when libc++ deprecates the feature and adds two tests that (1) pass
-# with deprecation suppressed, and (2) fail without deprecation suppression. We should instead translate libc++
-# un-deprecation macros to STL un-deprecation macros in the force-include header, and just skip tests when we
-# deprecate before they do.
+# Deprecation is a mess. We disable all deprecations in llvm-project/libcxx/test/support/msvc_stdlib_force_include.h
+# (external to this repo) to allow libc++ tests for deprecated features to pass, which breaks when libc++ deprecates
+# the feature and adds two tests that (1) pass with deprecation suppressed, and (2) fail without deprecation suppression.
+# We should instead translate libc++ un-deprecation macros to STL un-deprecation macros in the force-include header,
+# and just skip tests when we deprecate before they do.
 std/utilities/meta/meta.unary/meta.unary.prop/is_literal_type.deprecated.fail.cpp FAIL
 
 
diff --git a/tests/libcxx/skipped_tests.txt b/tests/libcxx/skipped_tests.txt
index 5c931e01bc..5b05324abc 100644
--- a/tests/libcxx/skipped_tests.txt
+++ b/tests/libcxx/skipped_tests.txt
@@ -221,11 +221,11 @@ containers\unord\unord.set\max_size.pass.cpp
 utilities\tuple\tuple.tuple\tuple.apply\apply_large_arity.pass.cpp
 utilities\tuple\tuple.tuple\tuple.cnstr\recursion_depth.pass.cpp
 
-# Deprecation is a mess. We disable all deprecations in msvc_stdlib_force_include.h to allow libc++ tests for
-# deprecated features to pass, which breaks when libc++ deprecates the feature and adds two tests that (1) pass
-# with deprecation suppressed, and (2) fail without deprecation suppression. We should instead translate libc++
-# un-deprecation macros to STL un-deprecation macros in the force-include header, and just skip tests when we
-# deprecate before they do.
+# Deprecation is a mess. We disable all deprecations in llvm-project/libcxx/test/support/msvc_stdlib_force_include.h
+# (external to this repo) to allow libc++ tests for deprecated features to pass, which breaks when libc++ deprecates
+# the feature and adds two tests that (1) pass with deprecation suppressed, and (2) fail without deprecation suppression.
+# We should instead translate libc++ un-deprecation macros to STL un-deprecation macros in the force-include header,
+# and just skip tests when we deprecate before they do.
 utilities\meta\meta.unary\meta.unary.prop\is_literal_type.deprecated.fail.cpp
 
 
diff --git a/tests/libcxx/usual_matrix.lst b/tests/libcxx/usual_matrix.lst
index 3c6d3fe786..193320fdd4 100644
--- a/tests/libcxx/usual_matrix.lst
+++ b/tests/libcxx/usual_matrix.lst
@@ -3,7 +3,8 @@
 
 RUNALL_INCLUDE ..\universal_prefix.lst
 RUNALL_CROSSLIST
-PM_CL="/EHsc /MTd /std:c++latest /permissive- /FImsvc_stdlib_force_include.h /wd4643 /D_STL_CALL_ABORT_INSTEAD_OF_INVALID_PARAMETER"
+# TRANSITION, LLVM-53957: _SILENCE_ALL_CXX23_DEPRECATION_WARNINGS belongs to llvm-project/libcxx/test/support/msvc_stdlib_force_include.h
+PM_CL="/EHsc /MTd /std:c++latest /permissive- /FImsvc_stdlib_force_include.h /wd4643 /D_STL_CALL_ABORT_INSTEAD_OF_INVALID_PARAMETER /D_SILENCE_ALL_CXX23_DEPRECATION_WARNINGS"
 RUNALL_CROSSLIST
 PM_CL="/analyze:autolog- /Zc:preprocessor"
 PM_COMPILER="clang-cl" PM_CL="-fno-ms-compatibility -fno-delayed-template-parsing"
diff --git a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
index b4765400c7..35346dc1b6 100644
--- a/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
+++ b/tests/std/tests/Dev11_0000000_null_forward_iterators/test.cpp
@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 #define _SILENCE_EXPERIMENTAL_FILESYSTEM_DEPRECATION_WARNING
 
 #include <array>
diff --git a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
index 35a271def5..545da00ef0 100644
--- a/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
+++ b/tests/std/tests/Dev11_0000000_user_defined_literals/test.cpp
@@ -3,6 +3,7 @@
 
 #define _HAS_DEPRECATED_RAW_STORAGE_ITERATOR 1
 #define _SILENCE_CXX17_RAW_STORAGE_ITERATOR_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 #define _SILENCE_EXPERIMENTAL_ERASE_DEPRECATION_WARNING
 
 #include <algorithm>
diff --git a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
index 6a33ce1099..268721302d 100644
--- a/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
+++ b/tests/std/tests/Dev11_0748972_function_crash_out_of_memory/test.cpp
@@ -1,6 +1,8 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
+
 #include <assert.h>
 #include <crtdbg.h>
 #include <functional>
diff --git a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
index 5af1ff3335..7a21362fb2 100644
--- a/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
+++ b/tests/std/tests/P0035R4_over_aligned_allocation/test.cpp
@@ -4,6 +4,7 @@
 #define _ENABLE_EXTENDED_ALIGNED_STORAGE
 #define _HAS_DEPRECATED_TEMPORARY_BUFFER 1
 #define _SILENCE_CXX17_TEMPORARY_BUFFER_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
 
 #include <array>
 #include <assert.h>
diff --git a/tests/std/tests/P0088R3_variant/test.cpp b/tests/std/tests/P0088R3_variant/test.cpp
index 461e719ec2..836a6edb92 100644
--- a/tests/std/tests/P0088R3_variant/test.cpp
+++ b/tests/std/tests/P0088R3_variant/test.cpp
@@ -38,6 +38,7 @@
 #define _HAS_DEPRECATED_RESULT_OF 1
 #define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
 #define _SILENCE_CXX20_VOLATILE_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 #define _LIBCXX_IN_DEVCRT
 #include <msvc_stdlib_force_include.h> // Must precede any other libc++ headers
 
diff --git a/tests/std/tests/P0220R1_polymorphic_memory_resources/test.cpp b/tests/std/tests/P0220R1_polymorphic_memory_resources/test.cpp
index 0f48053e20..48d56c52ea 100644
--- a/tests/std/tests/P0220R1_polymorphic_memory_resources/test.cpp
+++ b/tests/std/tests/P0220R1_polymorphic_memory_resources/test.cpp
@@ -2,6 +2,7 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
 #define _SILENCE_CXX17_POLYMORPHIC_ALLOCATOR_DESTROY_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 
 #include <algorithm>
 #include <cmath>
diff --git a/tests/std/tests/VSO_0000000_instantiate_type_traits/test.compile.pass.cpp b/tests/std/tests/VSO_0000000_instantiate_type_traits/test.compile.pass.cpp
index 6006b36a37..d5a54462d1 100644
--- a/tests/std/tests/VSO_0000000_instantiate_type_traits/test.compile.pass.cpp
+++ b/tests/std/tests/VSO_0000000_instantiate_type_traits/test.compile.pass.cpp
@@ -6,6 +6,7 @@
 #define _SILENCE_CXX17_IS_LITERAL_TYPE_DEPRECATION_WARNING
 #define _SILENCE_CXX17_RESULT_OF_DEPRECATION_WARNING
 #define _SILENCE_CXX20_IS_POD_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
 #define _USE_NAMED_IDL_NAMESPACE 1
 
 #include <array>
diff --git a/tests/tr1/tests/type_traits1/test.cpp b/tests/tr1/tests/type_traits1/test.cpp
index 0f2e378fa0..d07015289b 100644
--- a/tests/tr1/tests/type_traits1/test.cpp
+++ b/tests/tr1/tests/type_traits1/test.cpp
@@ -4,6 +4,9 @@
 // test <type_traits> header, part 1
 #define TEST_NAME "<type_traits>, part 1"
 
+#define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
+
 #include "tdefs.h"
 #include "typetr.h"
 #include <type_traits>
diff --git a/tests/tr1/tests/type_traits5/test.cpp b/tests/tr1/tests/type_traits5/test.cpp
index 87c05096a2..9cdf000555 100644
--- a/tests/tr1/tests/type_traits5/test.cpp
+++ b/tests/tr1/tests/type_traits5/test.cpp
@@ -5,6 +5,9 @@
 #define TEST_NAME "<type_traits>, part 5"
 
 #define _DISABLE_EXTENDED_ALIGNED_STORAGE 1
+#define _SILENCE_CXX23_ALIGNED_STORAGE_DEPRECATION_WARNING
+#define _SILENCE_CXX23_ALIGNED_UNION_DEPRECATION_WARNING
+
 #include "tdefs.h"
 #include "typetr.h"
 #include <limits.h>