diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index a6c658c..8877ec0 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -342,7 +342,7 @@
     ------------------------------------------------- -----------------
     ``__cpp_lib_stacktrace``                          *unimplemented*
     ------------------------------------------------- -----------------
-    ``__cpp_lib_stdatomic_h``                         ``202011L``
+    ``__cpp_lib_stdatomic_h``                         *unimplemented*
     ------------------------------------------------- -----------------
     ``__cpp_lib_string_contains``                     ``202011L``
     ------------------------------------------------- -----------------
diff --git a/libcxx/docs/Status/Cxx2bPapers.csv b/libcxx/docs/Status/Cxx2bPapers.csv
index 12fb513..c0ef688 100644
--- a/libcxx/docs/Status/Cxx2bPapers.csv
+++ b/libcxx/docs/Status/Cxx2bPapers.csv
@@ -1,6 +1,6 @@
 "Paper #","Group","Paper Name","Meeting","Status","First released version"
 "`P0881R7 <https://wg21.link/P0881R7>`__","LWG","A Proposal to add stacktrace library","Autumn 2020","",""
-"`P0943R6 <https://wg21.link/P0943R6>`__","LWG","Support C atomics in C++","Autumn 2020","|Complete|","15.0"
+"`P0943R6 <https://wg21.link/P0943R6>`__","LWG","Support C atomics in C++","Autumn 2020","",""
 "`P1048R1 <https://wg21.link/P1048R1>`__","LWG","A proposal for a type trait to detect scoped enumerations","Autumn 2020","|Complete|","12.0"
 "`P1679R3 <https://wg21.link/P1679R3>`__","LWG","string contains function","Autumn 2020","|Complete|","12.0"
 "","","","","",""
diff --git a/libcxx/include/CMakeLists.txt b/libcxx/include/CMakeLists.txt
index d463d20..fb2b5be 100644
--- a/libcxx/include/CMakeLists.txt
+++ b/libcxx/include/CMakeLists.txt
@@ -517,7 +517,6 @@
   span
   sstream
   stack
-  stdatomic.h
   stdbool.h
   stddef.h
   stdexcept
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
index a58a44a..7fed871 100644
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -540,7 +540,7 @@
 # error <atomic> is not implemented
 #endif
 #ifdef kill_dependency
-# error C++ standard library is incompatible with <stdatomic.h> before C++23. Please compile with -std=c++23.
+# error C++ standard library is incompatible with <stdatomic.h>
 #endif
 
 #define _LIBCPP_CHECK_STORE_MEMORY_ORDER(__m) \
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
index b958737..95ff1ec 100644
--- a/libcxx/include/module.modulemap
+++ b/libcxx/include/module.modulemap
@@ -50,10 +50,6 @@
       header "setjmp.h"
       export *
     }
-    module stdatomic_h {
-      header "stdatomic.h"
-      export *
-    }
     // FIXME: <stdalign.h> is missing.
     // <signal.h> provided by C library.
     // <stdarg.h> provided by compiler.
diff --git a/libcxx/include/stdatomic.h b/libcxx/include/stdatomic.h
deleted file mode 100644
index d9550c4..0000000
--- a/libcxx/include/stdatomic.h
+++ /dev/null
@@ -1,235 +0,0 @@
-// -*- C++ -*-
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef _LIBCPP_STDATOMIC_H
-#define _LIBCPP_STDATOMIC_H
-
-/*
-    stdatomic.h synopsis
-
-template<class T>
-  using std-atomic = std::atomic<T>;        // exposition only
-
-#define _Atomic(T) std-atomic<T>
-
-#define ATOMIC_BOOL_LOCK_FREE see below
-#define ATOMIC_CHAR_LOCK_FREE see below
-#define ATOMIC_CHAR16_T_LOCK_FREE see below
-#define ATOMIC_CHAR32_T_LOCK_FREE see below
-#define ATOMIC_WCHAR_T_LOCK_FREE see below
-#define ATOMIC_SHORT_LOCK_FREE see below
-#define ATOMIC_INT_LOCK_FREE see below
-#define ATOMIC_LONG_LOCK_FREE see below
-#define ATOMIC_LLONG_LOCK_FREE see below
-#define ATOMIC_POINTER_LOCK_FREE see below
-
-using std::memory_order                // see below
-using std::memory_order_relaxed        // see below
-using std::memory_order_consume        // see below
-using std::memory_order_acquire        // see below
-using std::memory_order_release        // see below
-using std::memory_order_acq_rel        // see below
-using std::memory_order_seq_cst        // see below
-
-using std::atomic_flag                 // see below
-
-using std::atomic_bool                 // see below
-using std::atomic_char                 // see below
-using std::atomic_schar                // see below
-using std::atomic_uchar                // see below
-using std::atomic_short                // see below
-using std::atomic_ushort               // see below
-using std::atomic_int                  // see below
-using std::atomic_uint                 // see below
-using std::atomic_long                 // see below
-using std::atomic_ulong                // see below
-using std::atomic_llong                // see below
-using std::atomic_ullong               // see below
-using std::atomic_char8_t              // see below
-using std::atomic_char16_t             // see below
-using std::atomic_char32_t             // see below
-using std::atomic_wchar_t              // see below
-using std::atomic_int8_t               // see below
-using std::atomic_uint8_t              // see below
-using std::atomic_int16_t              // see below
-using std::atomic_uint16_t             // see below
-using std::atomic_int32_t              // see below
-using std::atomic_uint32_t             // see below
-using std::atomic_int64_t              // see below
-using std::atomic_uint64_t             // see below
-using std::atomic_int_least8_t         // see below
-using std::atomic_uint_least8_t        // see below
-using std::atomic_int_least16_t        // see below
-using std::atomic_uint_least16_t       // see below
-using std::atomic_int_least32_t        // see below
-using std::atomic_uint_least32_t       // see below
-using std::atomic_int_least64_t        // see below
-using std::atomic_uint_least64_t       // see below
-using std::atomic_int_fast8_t          // see below
-using std::atomic_uint_fast8_t         // see below
-using std::atomic_int_fast16_t         // see below
-using std::atomic_uint_fast16_t        // see below
-using std::atomic_int_fast32_t         // see below
-using std::atomic_uint_fast32_t        // see below
-using std::atomic_int_fast64_t         // see below
-using std::atomic_uint_fast64_t        // see below
-using std::atomic_intptr_t             // see below
-using std::atomic_uintptr_t            // see below
-using std::atomic_size_t               // see below
-using std::atomic_ptrdiff_t            // see below
-using std::atomic_intmax_t             // see below
-using std::atomic_uintmax_t            // see below
-
-using std::atomic_is_lock_free                         // see below
-using std::atomic_load                                 // see below
-using std::atomic_load_explicit                        // see below
-using std::atomic_store                                // see below
-using std::atomic_store_explicit                       // see below
-using std::atomic_exchange                             // see below
-using std::atomic_exchange_explicit                    // see below
-using std::atomic_compare_exchange_strong              // see below
-using std::atomic_compare_exchange_strong_explicit     // see below
-using std::atomic_compare_exchange_weak                // see below
-using std::atomic_compare_exchange_weak_explicit       // see below
-using std::atomic_fetch_add                            // see below
-using std::atomic_fetch_add_explicit                   // see below
-using std::atomic_fetch_sub                            // see below
-using std::atomic_fetch_sub_explicit                   // see below
-using std::atomic_fetch_or                             // see below
-using std::atomic_fetch_or_explicit                    // see below
-using std::atomic_fetch_and                            // see below
-using std::atomic_fetch_and_explicit                   // see below
-using std::atomic_flag_test_and_set                    // see below
-using std::atomic_flag_test_and_set_explicit           // see below
-using std::atomic_flag_clear                           // see below
-using std::atomic_flag_clear_explicit                  // see below
-
-using std::atomic_thread_fence                         // see below
-using std::atomic_signal_fence                         // see below
-
-*/
-
-#include <__config>
-
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
-
-#if _LIBCPP_STD_VER > 20
-
-#include <atomic>
-#include <version>
-
-#ifdef _Atomic
-# undef _Atomic
-#endif
-
-#define _Atomic(_Tp) ::std::atomic<_Tp>
-
-using std::memory_order _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_relaxed _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_consume _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_acquire _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_release _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_acq_rel _LIBCPP_USING_IF_EXISTS;
-using std::memory_order_seq_cst _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_flag _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_bool _LIBCPP_USING_IF_EXISTS;
-using std::atomic_char _LIBCPP_USING_IF_EXISTS;
-using std::atomic_schar _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uchar _LIBCPP_USING_IF_EXISTS;
-using std::atomic_short _LIBCPP_USING_IF_EXISTS;
-using std::atomic_ushort _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint _LIBCPP_USING_IF_EXISTS;
-using std::atomic_long _LIBCPP_USING_IF_EXISTS;
-using std::atomic_ulong _LIBCPP_USING_IF_EXISTS;
-using std::atomic_llong _LIBCPP_USING_IF_EXISTS;
-using std::atomic_ullong _LIBCPP_USING_IF_EXISTS;
-using std::atomic_char8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_char16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_char32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_wchar_t _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_int8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int64_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint64_t _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_int_least8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_least8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_least16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_least16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_least32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_least32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_least64_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_least64_t _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_int_fast8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_fast8_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_fast16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_fast16_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_fast32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_fast32_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_int_fast64_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uint_fast64_t _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_intptr_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uintptr_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_size_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_ptrdiff_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_intmax_t _LIBCPP_USING_IF_EXISTS;
-using std::atomic_uintmax_t _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_compare_exchange_strong _LIBCPP_USING_IF_EXISTS;
-using std::atomic_compare_exchange_strong_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_compare_exchange_weak _LIBCPP_USING_IF_EXISTS;
-using std::atomic_compare_exchange_weak_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_exchange _LIBCPP_USING_IF_EXISTS;
-using std::atomic_exchange_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_add _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_add_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_and _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_and_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_or _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_or_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_sub _LIBCPP_USING_IF_EXISTS;
-using std::atomic_fetch_sub_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_flag_clear _LIBCPP_USING_IF_EXISTS;
-using std::atomic_flag_clear_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_flag_test_and_set _LIBCPP_USING_IF_EXISTS;
-using std::atomic_flag_test_and_set_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_is_lock_free _LIBCPP_USING_IF_EXISTS;
-using std::atomic_load _LIBCPP_USING_IF_EXISTS;
-using std::atomic_load_explicit _LIBCPP_USING_IF_EXISTS;
-using std::atomic_store _LIBCPP_USING_IF_EXISTS;
-using std::atomic_store_explicit _LIBCPP_USING_IF_EXISTS;
-
-using std::atomic_signal_fence _LIBCPP_USING_IF_EXISTS;
-using std::atomic_thread_fence _LIBCPP_USING_IF_EXISTS;
-
-#elif defined(_LIBCPP_COMPILER_CLANG_BASED)
-
-// Before C++23, we include the next <stdatomic.h> on the path to avoid hijacking
-// the header. We do this because Clang has historically shipped a <stdatomic.h>
-// header that would be available in all Standard modes, and we don't want to
-// break that use case.
-# if __has_include_next(<stdatomic.h>)
-#   include_next <stdatomic.h>
-# endif
-
-#endif // _LIBCPP_STD_VER > 20
-
-#endif // _LIBCPP_STDATOMIC_H
diff --git a/libcxx/include/version b/libcxx/include/version
index 5cbe474..3aed750 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -396,7 +396,7 @@
 // # define __cpp_lib_reference_from_temporary             202202L
 // # define __cpp_lib_spanstream                           202106L
 // # define __cpp_lib_stacktrace                           202011L
-# define __cpp_lib_stdatomic_h                          202011L
+// # define __cpp_lib_stdatomic_h                          202011L
 # define __cpp_lib_string_contains                      202011L
 # define __cpp_lib_string_resize_and_overwrite          202110L
 # define __cpp_lib_to_underlying                        202102L
diff --git a/libcxx/test/libcxx/atomics/stdatomic.h.syn/dont_hijack_header.compile.pass.cpp b/libcxx/test/libcxx/atomics/stdatomic.h.syn/dont_hijack_header.compile.pass.cpp
deleted file mode 100644
index f00c3ef..0000000
--- a/libcxx/test/libcxx/atomics/stdatomic.h.syn/dont_hijack_header.compile.pass.cpp
+++ /dev/null
@@ -1,23 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: libcpp-has-no-threads
-
-// This test ensures that we don't hijack the <stdatomic.h> header even when compiling
-// before C++23, since Clang used to provide that header before libc++ provided one.
-
-// On GCC, the compiler-provided <stdatomic.h> is not C++ friendly, so including <stdatomic.h>
-// doesn't work at all if we don't use the <stdatomic.h> provided by libc++ in C++23 and above.
-// XFAIL: (c++11 || c++14 || c++17 || c++20) && gcc
-
-#include <stdatomic.h>
-
-void f() {
-  atomic_int i; // just make sure the header isn't empty
-  (void)i;
-}
diff --git a/libcxx/test/libcxx/double_include.sh.cpp b/libcxx/test/libcxx/double_include.sh.cpp
index 7eda8fc..6e2c2ab 100644
--- a/libcxx/test/libcxx/double_include.sh.cpp
+++ b/libcxx/test/libcxx/double_include.sh.cpp
@@ -165,9 +165,6 @@
 #    include <sstream>
 #endif
 #include <stack>
-#ifndef _LIBCPP_HAS_NO_THREADS
-#    include <stdatomic.h>
-#endif
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdexcept>
diff --git a/libcxx/test/libcxx/min_max_macros.compile.pass.cpp b/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
index 2ff617a..4bde133 100644
--- a/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
+++ b/libcxx/test/libcxx/min_max_macros.compile.pass.cpp
@@ -254,10 +254,6 @@
 #endif
 #include <stack>
 TEST_MACROS();
-#ifndef _LIBCPP_HAS_NO_THREADS
-#    include <stdatomic.h>
-TEST_MACROS();
-#endif
 #include <stdbool.h>
 TEST_MACROS();
 #include <stddef.h>
diff --git a/libcxx/test/libcxx/nasty_macros.compile.pass.cpp b/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
index 7085551..d94e3b3 100644
--- a/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
+++ b/libcxx/test/libcxx/nasty_macros.compile.pass.cpp
@@ -275,9 +275,6 @@
 #    include <sstream>
 #endif
 #include <stack>
-#ifndef _LIBCPP_HAS_NO_THREADS
-#    include <stdatomic.h>
-#endif
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdexcept>
diff --git a/libcxx/test/libcxx/no_assert_include.compile.pass.cpp b/libcxx/test/libcxx/no_assert_include.compile.pass.cpp
index 34e0b67..37e88f7 100644
--- a/libcxx/test/libcxx/no_assert_include.compile.pass.cpp
+++ b/libcxx/test/libcxx/no_assert_include.compile.pass.cpp
@@ -160,9 +160,6 @@
 #    include <sstream>
 #endif
 #include <stack>
-#ifndef _LIBCPP_HAS_NO_THREADS
-#    include <stdatomic.h>
-#endif
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdexcept>
diff --git a/libcxx/test/std/atomics/stdatomic.h.syn/types.compile.pass.cpp b/libcxx/test/std/atomics/stdatomic.h.syn/types.compile.pass.cpp
deleted file mode 100644
index 6d2f810..0000000
--- a/libcxx/test/std/atomics/stdatomic.h.syn/types.compile.pass.cpp
+++ /dev/null
@@ -1,237 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// UNSUPPORTED: libcpp-has-no-threads
-
-// <stdatomic.h>
-
-// template<class T>
-//   using std-atomic = std::atomic<T>;        // exposition only
-//
-// #define _Atomic(T) std-atomic<T>
-//
-// #define ATOMIC_BOOL_LOCK_FREE see below
-// #define ATOMIC_CHAR_LOCK_FREE see below
-// #define ATOMIC_CHAR16_T_LOCK_FREE see below
-// #define ATOMIC_CHAR32_T_LOCK_FREE see below
-// #define ATOMIC_WCHAR_T_LOCK_FREE see below
-// #define ATOMIC_SHORT_LOCK_FREE see below
-// #define ATOMIC_INT_LOCK_FREE see below
-// #define ATOMIC_LONG_LOCK_FREE see below
-// #define ATOMIC_LLONG_LOCK_FREE see below
-// #define ATOMIC_POINTER_LOCK_FREE see below
-//
-// using std::memory_order                // see below
-// using std::memory_order_relaxed        // see below
-// using std::memory_order_consume        // see below
-// using std::memory_order_acquire        // see below
-// using std::memory_order_release        // see below
-// using std::memory_order_acq_rel        // see below
-// using std::memory_order_seq_cst        // see below
-//
-// using std::atomic_flag                 // see below
-//
-// using std::atomic_bool                 // see below
-// using std::atomic_char                 // see below
-// using std::atomic_schar                // see below
-// using std::atomic_uchar                // see below
-// using std::atomic_short                // see below
-// using std::atomic_ushort               // see below
-// using std::atomic_int                  // see below
-// using std::atomic_uint                 // see below
-// using std::atomic_long                 // see below
-// using std::atomic_ulong                // see below
-// using std::atomic_llong                // see below
-// using std::atomic_ullong               // see below
-// using std::atomic_char8_t              // see below
-// using std::atomic_char16_t             // see below
-// using std::atomic_char32_t             // see below
-// using std::atomic_wchar_t              // see below
-// using std::atomic_int8_t               // see below
-// using std::atomic_uint8_t              // see below
-// using std::atomic_int16_t              // see below
-// using std::atomic_uint16_t             // see below
-// using std::atomic_int32_t              // see below
-// using std::atomic_uint32_t             // see below
-// using std::atomic_int64_t              // see below
-// using std::atomic_uint64_t             // see below
-// using std::atomic_int_least8_t         // see below
-// using std::atomic_uint_least8_t        // see below
-// using std::atomic_int_least16_t        // see below
-// using std::atomic_uint_least16_t       // see below
-// using std::atomic_int_least32_t        // see below
-// using std::atomic_uint_least32_t       // see below
-// using std::atomic_int_least64_t        // see below
-// using std::atomic_uint_least64_t       // see below
-// using std::atomic_int_fast8_t          // see below
-// using std::atomic_uint_fast8_t         // see below
-// using std::atomic_int_fast16_t         // see below
-// using std::atomic_uint_fast16_t        // see below
-// using std::atomic_int_fast32_t         // see below
-// using std::atomic_uint_fast32_t        // see below
-// using std::atomic_int_fast64_t         // see below
-// using std::atomic_uint_fast64_t        // see below
-// using std::atomic_intptr_t             // see below
-// using std::atomic_uintptr_t            // see below
-// using std::atomic_size_t               // see below
-// using std::atomic_ptrdiff_t            // see below
-// using std::atomic_intmax_t             // see below
-// using std::atomic_uintmax_t            // see below
-//
-// using std::atomic_is_lock_free                         // see below
-// using std::atomic_load                                 // see below
-// using std::atomic_load_explicit                        // see below
-// using std::atomic_store                                // see below
-// using std::atomic_store_explicit                       // see below
-// using std::atomic_exchange                             // see below
-// using std::atomic_exchange_explicit                    // see below
-// using std::atomic_compare_exchange_strong              // see below
-// using std::atomic_compare_exchange_strong_explicit     // see below
-// using std::atomic_compare_exchange_weak                // see below
-// using std::atomic_compare_exchange_weak_explicit       // see below
-// using std::atomic_fetch_add                            // see below
-// using std::atomic_fetch_add_explicit                   // see below
-// using std::atomic_fetch_sub                            // see below
-// using std::atomic_fetch_sub_explicit                   // see below
-// using std::atomic_fetch_or                             // see below
-// using std::atomic_fetch_or_explicit                    // see below
-// using std::atomic_fetch_and                            // see below
-// using std::atomic_fetch_and_explicit                   // see below
-// using std::atomic_flag_test_and_set                    // see below
-// using std::atomic_flag_test_and_set_explicit           // see below
-// using std::atomic_flag_clear                           // see below
-// using std::atomic_flag_clear_explicit                  // see below
-//
-// using std::atomic_thread_fence                         // see below
-// using std::atomic_signal_fence                         // see below
-
-#include <stdatomic.h>
-#include <type_traits>
-
-#include "test_macros.h"
-
-static_assert(std::atomic<bool>::is_always_lock_free == (2 == ATOMIC_BOOL_LOCK_FREE));
-static_assert(std::atomic<char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
-static_assert(std::atomic<signed char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
-static_assert(std::atomic<unsigned char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
-static_assert(std::atomic<char16_t>::is_always_lock_free == (2 == ATOMIC_CHAR16_T_LOCK_FREE));
-static_assert(std::atomic<char32_t>::is_always_lock_free == (2 == ATOMIC_CHAR32_T_LOCK_FREE));
-#ifndef TEST_HAS_NO_WIDE_CHARACTERS
-static_assert(std::atomic<wchar_t>::is_always_lock_free == (2 == ATOMIC_WCHAR_T_LOCK_FREE));
-#endif
-static_assert(std::atomic<short>::is_always_lock_free == (2 == ATOMIC_SHORT_LOCK_FREE));
-static_assert(std::atomic<unsigned short>::is_always_lock_free == (2 == ATOMIC_SHORT_LOCK_FREE));
-static_assert(std::atomic<int>::is_always_lock_free == (2 == ATOMIC_INT_LOCK_FREE));
-static_assert(std::atomic<unsigned int>::is_always_lock_free == (2 == ATOMIC_INT_LOCK_FREE));
-static_assert(std::atomic<long>::is_always_lock_free == (2 == ATOMIC_LONG_LOCK_FREE));
-static_assert(std::atomic<unsigned long>::is_always_lock_free == (2 == ATOMIC_LONG_LOCK_FREE));
-static_assert(std::atomic<long long>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE));
-static_assert(std::atomic<unsigned long long>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE));
-static_assert(std::atomic<void*>::is_always_lock_free == (2 == ATOMIC_POINTER_LOCK_FREE));
-static_assert(std::atomic<std::nullptr_t>::is_always_lock_free == (2 == ATOMIC_POINTER_LOCK_FREE));
-
-void f() {
-  static_assert(std::is_same_v<std::atomic<char>, _Atomic(char)>);
-  static_assert(std::is_same_v<std::atomic<int>, _Atomic(int)>);
-  static_assert(std::is_same_v<std::atomic<const long>, _Atomic(const long)>);
-
-  static_assert(std::is_same_v<std::memory_order, ::memory_order>);
-  static_assert(std::memory_order_relaxed == ::memory_order_relaxed);
-  static_assert(std::memory_order_consume == ::memory_order_consume);
-  static_assert(std::memory_order_acquire == ::memory_order_acquire);
-  static_assert(std::memory_order_release == ::memory_order_release);
-  static_assert(std::memory_order_acq_rel == ::memory_order_acq_rel);
-  static_assert(std::memory_order_seq_cst == ::memory_order_seq_cst);
-
-  static_assert(std::is_same_v<std::atomic_flag, ::atomic_flag>);
-
-  static_assert(std::is_same_v<std::atomic<bool>, ::atomic_bool>);
-  static_assert(std::is_same_v<std::atomic<char>, ::atomic_char>);
-  static_assert(std::is_same_v<std::atomic<signed char>, ::atomic_schar>);
-  static_assert(std::is_same_v<std::atomic<unsigned char>, ::atomic_uchar>);
-  static_assert(std::is_same_v<std::atomic<short>, ::atomic_short>);
-  static_assert(std::is_same_v<std::atomic<unsigned short>, ::atomic_ushort>);
-  static_assert(std::is_same_v<std::atomic<int>, ::atomic_int>);
-  static_assert(std::is_same_v<std::atomic<unsigned int>, ::atomic_uint>);
-  static_assert(std::is_same_v<std::atomic<long>, ::atomic_long>);
-  static_assert(std::is_same_v<std::atomic<unsigned long>, ::atomic_ulong>);
-  static_assert(std::is_same_v<std::atomic<long long>, ::atomic_llong>);
-  static_assert(std::is_same_v<std::atomic<unsigned long long>, ::atomic_ullong>);
-
-#ifndef _LIBCPP_HAS_NO_CHAR8_T
-  static_assert(std::is_same_v<std::atomic<char8_t>,  ::atomic_char8_t>);
-#endif
-  static_assert(std::is_same_v<std::atomic<char16_t>, ::atomic_char16_t>);
-  static_assert(std::is_same_v<std::atomic<char32_t>, ::atomic_char32_t>);
-#ifndef TEST_HAS_NO_WIDE_CHARACTERS
-  static_assert(std::is_same_v<std::atomic<wchar_t>,  ::atomic_wchar_t>);
-#endif
-
-  static_assert(std::is_same_v<std::atomic<int8_t>,   ::atomic_int8_t>);
-  static_assert(std::is_same_v<std::atomic<uint8_t>,  ::atomic_uint8_t>);
-  static_assert(std::is_same_v<std::atomic<int16_t>,  ::atomic_int16_t>);
-  static_assert(std::is_same_v<std::atomic<uint16_t>, ::atomic_uint16_t>);
-  static_assert(std::is_same_v<std::atomic<int32_t>,  ::atomic_int32_t>);
-  static_assert(std::is_same_v<std::atomic<uint32_t>, ::atomic_uint32_t>);
-  static_assert(std::is_same_v<std::atomic<int64_t>,  ::atomic_int64_t>);
-  static_assert(std::is_same_v<std::atomic<uint64_t>, ::atomic_uint64_t>);
-
-  static_assert(std::is_same_v<std::atomic<int_least8_t>,   ::atomic_int_least8_t>);
-  static_assert(std::is_same_v<std::atomic<uint_least8_t>,  ::atomic_uint_least8_t>);
-  static_assert(std::is_same_v<std::atomic<int_least16_t>,  ::atomic_int_least16_t>);
-  static_assert(std::is_same_v<std::atomic<uint_least16_t>, ::atomic_uint_least16_t>);
-  static_assert(std::is_same_v<std::atomic<int_least32_t>,  ::atomic_int_least32_t>);
-  static_assert(std::is_same_v<std::atomic<uint_least32_t>, ::atomic_uint_least32_t>);
-  static_assert(std::is_same_v<std::atomic<int_least64_t>,  ::atomic_int_least64_t>);
-  static_assert(std::is_same_v<std::atomic<uint_least64_t>, ::atomic_uint_least64_t>);
-
-  static_assert(std::is_same_v<std::atomic<int_fast8_t>,    ::atomic_int_fast8_t>);
-  static_assert(std::is_same_v<std::atomic<uint_fast8_t>,   ::atomic_uint_fast8_t>);
-  static_assert(std::is_same_v<std::atomic<int_fast16_t>,   ::atomic_int_fast16_t>);
-  static_assert(std::is_same_v<std::atomic<uint_fast16_t>,  ::atomic_uint_fast16_t>);
-  static_assert(std::is_same_v<std::atomic<int_fast32_t>,   ::atomic_int_fast32_t>);
-  static_assert(std::is_same_v<std::atomic<uint_fast32_t>,  ::atomic_uint_fast32_t>);
-  static_assert(std::is_same_v<std::atomic<int_fast64_t>,   ::atomic_int_fast64_t>);
-  static_assert(std::is_same_v<std::atomic<uint_fast64_t>,  ::atomic_uint_fast64_t>);
-
-  static_assert(std::is_same_v<std::atomic<intptr_t>,  ::atomic_intptr_t>);
-  static_assert(std::is_same_v<std::atomic<uintptr_t>, ::atomic_uintptr_t>);
-  static_assert(std::is_same_v<std::atomic<size_t>,    ::atomic_size_t>);
-  static_assert(std::is_same_v<std::atomic<ptrdiff_t>, ::atomic_ptrdiff_t>);
-  static_assert(std::is_same_v<std::atomic<intmax_t>,  ::atomic_intmax_t>);
-  static_assert(std::is_same_v<std::atomic<uintmax_t>, ::atomic_uintmax_t>);
-
-  // Just check that the symbols in the global namespace are visible.
-  using ::atomic_compare_exchange_strong;
-  using ::atomic_compare_exchange_strong_explicit;
-  using ::atomic_compare_exchange_weak;
-  using ::atomic_compare_exchange_weak_explicit;
-  using ::atomic_exchange;
-  using ::atomic_exchange_explicit;
-  using ::atomic_fetch_add;
-  using ::atomic_fetch_add_explicit;
-  using ::atomic_fetch_and;
-  using ::atomic_fetch_and_explicit;
-  using ::atomic_fetch_or;
-  using ::atomic_fetch_or_explicit;
-  using ::atomic_fetch_sub;
-  using ::atomic_fetch_sub_explicit;
-  using ::atomic_flag_clear;
-  using ::atomic_flag_clear_explicit;
-  using ::atomic_flag_test_and_set;
-  using ::atomic_flag_test_and_set_explicit;
-  using ::atomic_is_lock_free;
-  using ::atomic_load;
-  using ::atomic_load_explicit;
-  using ::atomic_store;
-  using ::atomic_store_explicit;
-
-  using ::atomic_signal_fence;
-  using ::atomic_thread_fence;
-}
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/stdatomic.h.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/stdatomic.h.version.pass.cpp
deleted file mode 100644
index 8c55b8c..0000000
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/stdatomic.h.version.pass.cpp
+++ /dev/null
@@ -1,62 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// WARNING: This test was generated by generate_feature_test_macro_components.py
-// and should not be edited manually.
-//
-// clang-format off
-
-// UNSUPPORTED: libcpp-has-no-threads
-
-// <stdatomic.h>
-
-// Test the feature test macros defined by <stdatomic.h>
-
-/*  Constant                 Value
-    __cpp_lib_stdatomic_h    202011L [C++2b]
-*/
-
-#include <stdatomic.h>
-#include "test_macros.h"
-
-#if TEST_STD_VER < 14
-
-# ifdef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should not be defined before c++2b"
-# endif
-
-#elif TEST_STD_VER == 14
-
-# ifdef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should not be defined before c++2b"
-# endif
-
-#elif TEST_STD_VER == 17
-
-# ifdef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should not be defined before c++2b"
-# endif
-
-#elif TEST_STD_VER == 20
-
-# ifdef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should not be defined before c++2b"
-# endif
-
-#elif TEST_STD_VER > 20
-
-# ifndef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should be defined in c++2b"
-# endif
-# if __cpp_lib_stdatomic_h != 202011L
-#   error "__cpp_lib_stdatomic_h should have the value 202011L in c++2b"
-# endif
-
-#endif // TEST_STD_VER > 20
-
-int main(int, char**) { return 0; }
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
index 43df8d7..d69ae81 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.pass.cpp
@@ -4848,11 +4848,17 @@
 #   error "__cpp_lib_starts_ends_with should have the value 201711L in c++2b"
 # endif
 
-# ifndef __cpp_lib_stdatomic_h
-#   error "__cpp_lib_stdatomic_h should be defined in c++2b"
-# endif
-# if __cpp_lib_stdatomic_h != 202011L
-#   error "__cpp_lib_stdatomic_h should have the value 202011L in c++2b"
+# if !defined(_LIBCPP_VERSION)
+#   ifndef __cpp_lib_stdatomic_h
+#     error "__cpp_lib_stdatomic_h should be defined in c++2b"
+#   endif
+#   if __cpp_lib_stdatomic_h != 202011L
+#     error "__cpp_lib_stdatomic_h should have the value 202011L in c++2b"
+#   endif
+# else // _LIBCPP_VERSION
+#   ifdef __cpp_lib_stdatomic_h
+#     error "__cpp_lib_stdatomic_h should not be defined because it is unimplemented in libc++!"
+#   endif
 # endif
 
 # ifndef __cpp_lib_string_contains
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index 1daaea0..f2140ed 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -664,6 +664,7 @@
     "name": "__cpp_lib_stdatomic_h",
     "values": { "c++2b": 202011 },
     "headers": ["stdatomic.h"],
+    "unimplemented": True,
   }, {
     "name": "__cpp_lib_string_contains",
     "values": { "c++2b": 202011 },
@@ -785,8 +786,7 @@
   "regex": ["UNSUPPORTED: libcpp-has-no-localization"],
   "semaphore": ["UNSUPPORTED: libcpp-has-no-threads"],
   "shared_mutex": ["UNSUPPORTED: libcpp-has-no-threads"],
-  "stdatomic.h": ["UNSUPPORTED: libcpp-has-no-threads"],
-  "thread": ["UNSUPPORTED: libcpp-has-no-threads"],
+  "thread": ["UNSUPPORTED: libcpp-has-no-threads"]
 }
 
 def get_std_dialects():
diff --git a/libcxx/utils/generate_header_tests.py b/libcxx/utils/generate_header_tests.py
index 6783972..55bbc58 100755
--- a/libcxx/utils/generate_header_tests.py
+++ b/libcxx/utils/generate_header_tests.py
@@ -27,7 +27,6 @@
     "mutex": ["ifndef _LIBCPP_HAS_NO_THREADS"],
     "semaphore": ["ifndef _LIBCPP_HAS_NO_THREADS"],
     "shared_mutex": ["ifndef _LIBCPP_HAS_NO_THREADS"],
-    "stdatomic.h": ["ifndef _LIBCPP_HAS_NO_THREADS"],
     "thread": ["ifndef _LIBCPP_HAS_NO_THREADS"],
 
     "filesystem": ["ifndef _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY"],