diff --git a/libcxx/include/atomic b/libcxx/include/atomic
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -48,6 +48,7 @@
 
 #define ATOMIC_BOOL_LOCK_FREE unspecified
 #define ATOMIC_CHAR_LOCK_FREE unspecified
+#define ATOMIC_CHAR8_T_LOCK_FREE unspecified // C++20
 #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
 #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
 #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
@@ -465,6 +466,7 @@
 typedef atomic<unsigned long>      atomic_ulong;
 typedef atomic<long long>          atomic_llong;
 typedef atomic<unsigned long long> atomic_ullong;
+typedef atomic<char8_t>            atomic_char8_t; // C++20
 typedef atomic<char16_t>           atomic_char16_t;
 typedef atomic<char32_t>           atomic_char32_t;
 typedef atomic<wchar_t>            atomic_wchar_t;
@@ -1125,6 +1127,9 @@
 #if defined(__CLANG_ATOMIC_BOOL_LOCK_FREE)
 # define ATOMIC_BOOL_LOCK_FREE      __CLANG_ATOMIC_BOOL_LOCK_FREE
 # define ATOMIC_CHAR_LOCK_FREE      __CLANG_ATOMIC_CHAR_LOCK_FREE
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+# define ATOMIC_CHAR8_T_LOCK_FREE   __CLANG_ATOMIC_CHAR8_T_LOCK_FREE
+#endif
 # define ATOMIC_CHAR16_T_LOCK_FREE  __CLANG_ATOMIC_CHAR16_T_LOCK_FREE
 # define ATOMIC_CHAR32_T_LOCK_FREE  __CLANG_ATOMIC_CHAR32_T_LOCK_FREE
 # define ATOMIC_WCHAR_T_LOCK_FREE   __CLANG_ATOMIC_WCHAR_T_LOCK_FREE
@@ -1136,6 +1141,9 @@
 #elif defined(__GCC_ATOMIC_BOOL_LOCK_FREE)
 # define ATOMIC_BOOL_LOCK_FREE      __GCC_ATOMIC_BOOL_LOCK_FREE
 # define ATOMIC_CHAR_LOCK_FREE      __GCC_ATOMIC_CHAR_LOCK_FREE
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+# define ATOMIC_CHAR8_T_LOCK_FREE   __GCC_ATOMIC_CHAR8_T_LOCK_FREE
+#endif
 # define ATOMIC_CHAR16_T_LOCK_FREE  __GCC_ATOMIC_CHAR16_T_LOCK_FREE
 # define ATOMIC_CHAR32_T_LOCK_FREE  __GCC_ATOMIC_CHAR32_T_LOCK_FREE
 # define ATOMIC_WCHAR_T_LOCK_FREE   __GCC_ATOMIC_WCHAR_T_LOCK_FREE
@@ -1450,6 +1458,9 @@
 template<> struct __cxx_is_always_lock_free<char> { enum { __value = 2 == ATOMIC_CHAR_LOCK_FREE }; };
 template<> struct __cxx_is_always_lock_free<signed char> { enum { __value = 2 == ATOMIC_CHAR_LOCK_FREE }; };
 template<> struct __cxx_is_always_lock_free<unsigned char> { enum { __value = 2 == ATOMIC_CHAR_LOCK_FREE }; };
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+template<> struct __cxx_is_always_lock_free<char8_t> { enum { __value = 2 == ATOMIC_CHAR8_T_LOCK_FREE }; };
+#endif
 template<> struct __cxx_is_always_lock_free<char16_t> { enum { __value = 2 == ATOMIC_CHAR16_T_LOCK_FREE }; };
 template<> struct __cxx_is_always_lock_free<char32_t> { enum { __value = 2 == ATOMIC_CHAR32_T_LOCK_FREE }; };
 template<> struct __cxx_is_always_lock_free<wchar_t> { enum { __value = 2 == ATOMIC_WCHAR_T_LOCK_FREE }; };
@@ -2721,6 +2732,9 @@
 typedef atomic<unsigned long>      atomic_ulong;
 typedef atomic<long long>          atomic_llong;
 typedef atomic<unsigned long long> atomic_ullong;
+#ifndef _LIBCPP_NO_HAS_CHAR8_T
+typedef atomic<char8_t>            atomic_char8_t;
+#endif
 typedef atomic<char16_t>           atomic_char16_t;
 typedef atomic<char32_t>           atomic_char32_t;
 typedef atomic<wchar_t>            atomic_wchar_t;
diff --git a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
--- a/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
@@ -74,6 +74,9 @@
     CHECK_ALWAYS_LOCK_FREE(char);
     CHECK_ALWAYS_LOCK_FREE(signed char);
     CHECK_ALWAYS_LOCK_FREE(unsigned char);
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    CHECK_ALWAYS_LOCK_FREE(char8_t);
+#endif
     CHECK_ALWAYS_LOCK_FREE(char16_t);
     CHECK_ALWAYS_LOCK_FREE(char32_t);
     CHECK_ALWAYS_LOCK_FREE(wchar_t);
@@ -122,6 +125,9 @@
     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), "");
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    static_assert(std::atomic<char8_t>::is_always_lock_free == (2 == ATOMIC_CHAR8_T_LOCK_FREE), "");
+#endif
     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), "");
     static_assert(std::atomic<wchar_t>::is_always_lock_free == (2 == ATOMIC_WCHAR_T_LOCK_FREE), "");
diff --git a/libcxx/test/std/atomics/atomics.lockfree/lockfree.pass.cpp b/libcxx/test/std/atomics/atomics.lockfree/lockfree.pass.cpp
--- a/libcxx/test/std/atomics/atomics.lockfree/lockfree.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.lockfree/lockfree.pass.cpp
@@ -12,6 +12,7 @@
 
 // #define ATOMIC_BOOL_LOCK_FREE unspecified
 // #define ATOMIC_CHAR_LOCK_FREE unspecified
+// #define ATOMIC_CHAR8_T_LOCK_FREE unspecified // C++20
 // #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
 // #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
 // #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
@@ -34,6 +35,11 @@
     assert(ATOMIC_CHAR_LOCK_FREE == 0 ||
            ATOMIC_CHAR_LOCK_FREE == 1 ||
            ATOMIC_CHAR_LOCK_FREE == 2);
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    assert(ATOMIC_CHAR8_T_LOCK_FREE == 0 ||
+           ATOMIC_CHAR8_T_LOCK_FREE == 1 ||
+           ATOMIC_CHAR8_T_LOCK_FREE == 2);
+#endif
     assert(ATOMIC_CHAR16_T_LOCK_FREE == 0 ||
            ATOMIC_CHAR16_T_LOCK_FREE == 1 ||
            ATOMIC_CHAR16_T_LOCK_FREE == 2);
diff --git a/libcxx/test/std/atomics/atomics.types.generic/integral.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/integral.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.generic/integral.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/integral.pass.cpp
@@ -180,6 +180,9 @@
     test<std::atomic_ulong, unsigned long>();
     test<std::atomic_llong, long long>();
     test<std::atomic_ullong, unsigned long long>();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    test<std::atomic_char8_t, char8_t>();
+#endif
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
     test<std::atomic_char16_t, char16_t>();
     test<std::atomic_char32_t, char32_t>();
diff --git a/libcxx/test/std/atomics/atomics.types.generic/integral_typedefs.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/integral_typedefs.pass.cpp
--- a/libcxx/test/std/atomics/atomics.types.generic/integral_typedefs.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/integral_typedefs.pass.cpp
@@ -21,6 +21,7 @@
 // typedef atomic<unsigned long>      atomic_ulong;
 // typedef atomic<long long>          atomic_llong;
 // typedef atomic<unsigned long long> atomic_ullong;
+// typedef atomic<char8_t>            atomic_char8_t; // C++20
 // typedef atomic<char16_t>           atomic_char16_t;
 // typedef atomic<char32_t>           atomic_char32_t;
 // typedef atomic<wchar_t>            atomic_wchar_t;
@@ -56,6 +57,9 @@
     static_assert((std::is_same<std::atomic<long long>, std::atomic_llong>::value), "");
     static_assert((std::is_same<std::atomic<unsigned long long>, std::atomic_ullong>::value), "");
     static_assert((std::is_same<std::atomic<wchar_t>, std::atomic_wchar_t>::value), "");
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    static_assert((std::is_same<std::atomic<char8_t>, std::atomic_char8_t>::value), "");
+#endif
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
     static_assert((std::is_same<std::atomic<char16_t>, std::atomic_char16_t>::value), "");
     static_assert((std::is_same<std::atomic<char32_t>, std::atomic_char32_t>::value), "");
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_helpers.h b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_helpers.h
--- a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_helpers.h
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_helpers.h
@@ -83,6 +83,9 @@
         TestFunctor<long long>()();
         TestFunctor<unsigned long long>()();
         TestFunctor<wchar_t>();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+        TestFunctor<char8_t>()();
+#endif
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
         TestFunctor<char16_t>()();
         TestFunctor<char32_t>()();
diff --git a/libcxx/test/std/atomics/types.pass.cpp b/libcxx/test/std/atomics/types.pass.cpp
--- a/libcxx/test/std/atomics/types.pass.cpp
+++ b/libcxx/test/std/atomics/types.pass.cpp
@@ -112,6 +112,9 @@
     test<unsigned long>      ();
     test<long long>          ();
     test<unsigned long long> ();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    test<char8_t>            ();
+#endif
     test<char16_t>           ();
     test<char32_t>           ();
     test<wchar_t>            ();