diff --git a/libcxx/include/__string b/libcxx/include/__string
--- a/libcxx/include/__string
+++ b/libcxx/include/__string
@@ -47,7 +47,9 @@
 
 template <> struct char_traits<char>;
 template <> struct char_traits<wchar_t>;
-template <> struct char_traits<char8_t>;  // c++20
+template <> struct char_traits<char8_t>;  // C++20
+template <> struct char_traits<char16_t>;
+template <> struct char_traits<char32_t>;
 
 }  // std
 
diff --git a/libcxx/include/iosfwd b/libcxx/include/iosfwd
--- a/libcxx/include/iosfwd
+++ b/libcxx/include/iosfwd
@@ -84,8 +84,11 @@
 typedef basic_fstream<wchar_t>       wfstream;
 
 template <class state> class fpos;
-typedef fpos<char_traits<char>::state_type>    streampos;
-typedef fpos<char_traits<wchar_t>::state_type> wstreampos;
+using streampos  = fpos<char_traits<char>::state_type>;
+using wstreampos = fpos<char_traits<wchar_t>::state_type>;
+using u8streampos = fpos<char_traits<char8_t>::state_type>; // C++20
+using u16streampos = fpos<char_traits<char16_t>::state_type>;
+using u32streampos = fpos<char_traits<char32_t>::state_type>;
 
 }  // std
 
diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -69,6 +69,9 @@
 
 template <> struct char_traits<char>;
 template <> struct char_traits<wchar_t>;
+template <> struct char_traits<char8_t>;  // C++20
+template <> struct char_traits<char16_t>;
+template <> struct char_traits<char32_t>;
 
 template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT> >
 class basic_string
@@ -450,6 +453,7 @@
 
 typedef basic_string<char>    string;
 typedef basic_string<wchar_t> wstring;
+typedef basic_string<char8_t> u8string; // C++20
 typedef basic_string<char16_t> u16string;
 typedef basic_string<char32_t> u32string;
 
@@ -494,12 +498,14 @@
 wstring to_wstring(long double val);
 
 template <> struct hash<string>;
+template <> struct hash<u8string>; // C++20
 template <> struct hash<u16string>;
 template <> struct hash<u32string>;
 template <> struct hash<wstring>;
 
 basic_string<char>     operator "" s( const char *str,     size_t len ); // C++14
 basic_string<wchar_t>  operator "" s( const wchar_t *str,  size_t len ); // C++14
+basic_string<char8_t>  operator "" s( const char8_t *str,  size_t len ); // C++20
 basic_string<char16_t> operator "" s( const char16_t *str, size_t len ); // C++14
 basic_string<char32_t> operator "" s( const char32_t *str, size_t len ); // C++14
 
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -48,6 +48,7 @@
 
     // basic_string_view typedef names
     typedef basic_string_view<char> string_view;
+    typedef basic_string_view<char8_t> u8string_view; // C++20
     typedef basic_string_view<char16_t> u16string_view;
     typedef basic_string_view<char32_t> u32string_view;
     typedef basic_string_view<wchar_t> wstring_view;
@@ -161,12 +162,14 @@
   // 7.11, Hash support
   template <class T> struct hash;
   template <> struct hash<string_view>;
+  template <> struct hash<u8string_view>; // C++20
   template <> struct hash<u16string_view>;
   template <> struct hash<u32string_view>;
   template <> struct hash<wstring_view>;
 
   constexpr basic_string_view<char>     operator "" sv( const char *str,     size_t len ) noexcept;
   constexpr basic_string_view<wchar_t>  operator "" sv( const wchar_t *str,  size_t len ) noexcept;
+  constexpr basic_string_view<char8_t>  operator "" sv( const char8_t *str,  size_t len ) noexcept; // C++20
   constexpr basic_string_view<char16_t> operator "" sv( const char16_t *str, size_t len ) noexcept;
   constexpr basic_string_view<char32_t> operator "" sv( const char32_t *str, size_t len ) noexcept;
 
diff --git a/libcxx/test/std/language.support/support.limits/limits/is_specialized.pass.cpp b/libcxx/test/std/language.support/support.limits/limits/is_specialized.pass.cpp
--- a/libcxx/test/std/language.support/support.limits/limits/is_specialized.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/limits/is_specialized.pass.cpp
@@ -46,6 +46,9 @@
     test<bool>();
     test<char>();
     test<wchar_t>();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    test<char8_t>();
+#endif
 #ifndef _LIBCPP_HAS_NO_UNICODE_CHARS
     test<char16_t>();
     test<char32_t>();
diff --git a/libcxx/test/std/strings/basic.string.hash/char_type_hash.fail.cpp b/libcxx/test/std/strings/basic.string.hash/char_type_hash.fail.cpp
--- a/libcxx/test/std/strings/basic.string.hash/char_type_hash.fail.cpp
+++ b/libcxx/test/std/strings/basic.string.hash/char_type_hash.fail.cpp
@@ -55,14 +55,21 @@
 template <class CharT>
 void test() {
     typedef std::basic_string<CharT, trait<CharT> > str_t;
-    std::hash<str_t>
-        h; // expected-error-re 4 {{{{call to implicitly-deleted default constructor of 'std::hash<str_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+    std::hash<str_t> h;
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    // expected-error-re@-2 5 {{{{call to implicitly-deleted default constructor of 'std::hash<str_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+#else
+    // expected-error-re@-4 4 {{{{call to implicitly-deleted default constructor of 'std::hash<str_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+#endif
     (void)h;
 }
 
 int main(int, char**) {
     test<char>();
     test<wchar_t>();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    test<char8_t>();
+#endif
     test<char16_t>();
     test<char32_t>();
 
diff --git a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/types.pass.cpp b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/types.pass.cpp
--- a/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/types.pass.cpp
+++ b/libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/types.pass.cpp
@@ -11,10 +11,10 @@
 
 // template<> struct char_traits<char8_t>
 
-// typedef char8_t       char_type;
+// typedef char8_t        char_type;
 // typedef unsigned int   int_type;
 // typedef streamoff      off_type;
-// typedef u16streampos   pos_type;
+// typedef u8streampos    pos_type;
 // typedef mbstate_t      state_type;
 
 #include <string>
@@ -29,7 +29,7 @@
     static_assert((std::is_same<std::char_traits<char8_t>::char_type,  char8_t>::value), "");
     static_assert((std::is_same<std::char_traits<char8_t>::int_type,   unsigned int>::value), "");
     static_assert((std::is_same<std::char_traits<char8_t>::off_type,   std::streamoff>::value), "");
-    static_assert((std::is_same<std::char_traits<char8_t>::pos_type,   std::u16streampos>::value), "");
+    static_assert((std::is_same<std::char_traits<char8_t>::pos_type,   std::u8streampos>::value), "");
     static_assert((std::is_same<std::char_traits<char8_t>::state_type, std::mbstate_t>::value), "");
 #endif
 
diff --git a/libcxx/test/std/strings/string.view/string.view.hash/char_type.hash.fail.cpp b/libcxx/test/std/strings/string.view/string.view.hash/char_type.hash.fail.cpp
--- a/libcxx/test/std/strings/string.view/string.view.hash/char_type.hash.fail.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.hash/char_type.hash.fail.cpp
@@ -56,14 +56,21 @@
 template <class CharT>
 void test() {
     typedef std::basic_string_view<CharT, trait<CharT> > strv_t;
-    std::hash<strv_t>
-        h; // expected-error-re 4 {{{{call to implicitly-deleted default constructor of 'std::hash<strv_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+    std::hash<strv_t> h;
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    // expected-error-re@-2 5 {{{{call to implicitly-deleted default constructor of 'std::hash<strv_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+#else
+    // expected-error-re@-4 4 {{{{call to implicitly-deleted default constructor of 'std::hash<strv_t>'|implicit instantiation of undefined template}} {{.+}}}}}}
+#endif
     (void)h;
 }
 
 int main(int, char**) {
     test<char>();
     test<wchar_t>();
+#if TEST_STD_VER > 17 && defined(__cpp_char8_t)
+    test<char8_t>();
+#endif
     test<char16_t>();
     test<char32_t>();