diff --git a/libcxx/include/__iterator/concepts.h b/libcxx/include/__iterator/concepts.h
--- a/libcxx/include/__iterator/concepts.h
+++ b/libcxx/include/__iterator/concepts.h
@@ -96,6 +96,18 @@
   input_or_output_iterator<_Ip> &&
   __weakly_equality_comparable_with<_Sp, _Ip>;
 
+template<class, class>
+inline constexpr bool disable_sized_sentinel_for = false;
+
+template<class _Sp, class _Ip>
+concept sized_sentinel_for =
+  sentinel_for<_Sp, _Ip> &&
+  !disable_sized_sentinel_for<remove_cv_t<_Sp>, remove_cv_t<_Ip> > &&
+  requires(const _Ip& __i, const _Sp& __s) {
+    { __s - __i } -> same_as<iter_difference_t<_Ip> >;
+    { __i - __s } -> same_as<iter_difference_t<_Ip> >;
+  };
+
 // clang-format on
 
 #endif // !defined(_LIBCPP_HAS_NO_RANGES)
diff --git a/libcxx/include/iterator b/libcxx/include/iterator
--- a/libcxx/include/iterator
+++ b/libcxx/include/iterator
@@ -68,6 +68,13 @@
 template<class S, class I>
   concept sentinel_for = see below;                        // since C++20
 
+// [iterator.concept.sizedsentinel], concept sized_sentinel_for
+template<class S, class I>
+  inline constexpr bool disable_sized_sentinel_for = false;
+
+template<class S, class I>
+  concept sized_sentinel_for = see below;
+
 template<class Category, class T, class Distance = ptrdiff_t,
          class Pointer = T*, class Reference = T&>
 struct iterator
@@ -458,6 +465,7 @@
 #include <__iterator/iter_move.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/readable_traits.h>
+#include <__iterator/concepts.h>
 #include <__memory/addressof.h>
 #include <__memory/pointer_traits.h>
 #include <version>
diff --git a/libcxx/test/std/containers/associative/map/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/associative/map/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/associative/map/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/iterator_concept_conformance.compile.pass.cpp
@@ -30,6 +30,8 @@
 static_assert(std::sentinel_for<iterator, const_iterator>);
 static_assert(!std::sentinel_for<iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
 
 static_assert(std::indirectly_readable<const_iterator>);
 static_assert(!std::indirectly_writable<const_iterator, value_type>);
@@ -39,3 +41,5 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/associative/multimap/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/associative/multimap/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/associative/multimap/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/associative/multimap/iterator_concept_conformance.compile.pass.cpp
@@ -30,6 +30,8 @@
 static_assert(std::sentinel_for<iterator, const_iterator>);
 static_assert(!std::sentinel_for<iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
 
 static_assert(std::indirectly_readable<const_iterator>);
 static_assert(!std::indirectly_writable<const_iterator, value_type>);
@@ -39,3 +41,5 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/associative/multiset/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/associative/multiset/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/associative/multiset/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/associative/multiset/iterator_concept_conformance.compile.pass.cpp
@@ -30,6 +30,8 @@
 static_assert(std::sentinel_for<iterator, const_iterator>);
 static_assert(!std::sentinel_for<iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
 
 static_assert(std::indirectly_readable<const_iterator>);
 static_assert(!std::indirectly_writable<const_iterator, value_type>);
@@ -37,3 +39,5 @@
 static_assert(std::sentinel_for<const_iterator, iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/associative/set/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/associative/set/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/associative/set/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/associative/set/iterator_concept_conformance.compile.pass.cpp
@@ -30,6 +30,8 @@
 static_assert(std::sentinel_for<iterator, const_iterator>);
 static_assert(!std::sentinel_for<iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
 
 static_assert(std::indirectly_readable<const_iterator>);
 static_assert(!std::indirectly_writable<const_iterator, value_type>);
@@ -39,3 +41,5 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/sequences/array/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/sequences/array/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/sequences/array/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/sequences/array/iterator_concept_conformance.compile.pass.cpp
@@ -38,3 +38,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/sequences/deque/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/sequences/deque/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/sequences/deque/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/sequences/deque/iterator_concept_conformance.compile.pass.cpp
@@ -39,3 +39,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/sequences/forwardlist/forwardlist.iter/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.iter/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/sequences/forwardlist/forwardlist.iter/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/sequences/forwardlist/forwardlist.iter/iterator_concept_conformance.compile.pass.cpp
@@ -26,6 +26,8 @@
 static_assert(std::input_or_output_iterator<iterator>);
 static_assert(std::sentinel_for<iterator, iterator>);
 static_assert(std::sentinel_for<iterator, const_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_iterator>);
 
 static_assert(std::indirectly_readable<const_iterator>);
 static_assert(!std::indirectly_writable<const_iterator, value_type>);
@@ -33,3 +35,5 @@
 static_assert(std::input_or_output_iterator<const_iterator>);
 static_assert(std::sentinel_for<const_iterator, iterator>);
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_iterator>);
diff --git a/libcxx/test/std/containers/sequences/vector.bool/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/sequences/vector.bool/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/sequences/vector.bool/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/sequences/vector.bool/iterator_concept_conformance.compile.pass.cpp
@@ -39,3 +39,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/sequences/vector/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/sequences/vector/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/sequences/vector/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/sequences/vector/iterator_concept_conformance.compile.pass.cpp
@@ -39,3 +39,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/containers/unord/unord.map/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/unord/unord.map/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.map/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.map/iterator_concept_conformance.compile.pass.cpp
@@ -54,3 +54,8 @@
 static_assert(!std::sentinel_for<const_local_iterator, const_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, local_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, const_local_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_iterator>);
diff --git a/libcxx/test/std/containers/unord/unord.multimap/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/unord/unord.multimap/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.multimap/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.multimap/iterator_concept_conformance.compile.pass.cpp
@@ -57,3 +57,8 @@
 static_assert(!std::sentinel_for<const_local_iterator, const_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, local_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, const_local_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_iterator>);
\ No newline at end of file
diff --git a/libcxx/test/std/containers/unord/unord.multiset/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/unord/unord.multiset/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/unord/unord.multiset/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.multiset/iterator_concept_conformance.compile.pass.cpp
@@ -57,3 +57,8 @@
 static_assert(!std::sentinel_for<const_local_iterator, const_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, local_iterator>);
 static_assert(std::sentinel_for<const_local_iterator, const_local_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_iterator>);
diff --git a/libcxx/test/std/containers/views/span.iterators/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/containers/views/span.iterators/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/containers/views/span.iterators/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/containers/views/span.iterators/iterator_concept_conformance.compile.pass.cpp
@@ -26,3 +26,5 @@
 static_assert(std::input_or_output_iterator<iterator>);
 static_assert(std::sentinel_for<iterator, iterator>);
 static_assert(!std::sentinel_for<iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
diff --git a/libcxx/test/std/input.output/filesystems/class.directory_iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/input.output/filesystems/class.directory_iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/input.output/filesystems/class.directory_iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/input.output/filesystems/class.directory_iterator/iterator_concept_conformance.compile.pass.cpp
@@ -22,6 +22,7 @@
 static_assert(!std::incrementable<fs::directory_iterator>);
 static_assert(std::input_or_output_iterator<fs::directory_iterator>);
 static_assert(std::sentinel_for<fs::directory_iterator, fs::directory_iterator>);
+static_assert(!std::sized_sentinel_for<fs::directory_iterator, fs::directory_iterator>);
 
 static_assert(std::indirectly_readable<fs::recursive_directory_iterator>);
 static_assert(
@@ -30,3 +31,4 @@
 static_assert(!std::incrementable<fs::recursive_directory_iterator>);
 static_assert(std::input_or_output_iterator<fs::recursive_directory_iterator>);
 static_assert(std::sentinel_for<fs::recursive_directory_iterator, fs::recursive_directory_iterator>);
+static_assert(!std::sized_sentinel_for<fs::recursive_directory_iterator, fs::recursive_directory_iterator>);
diff --git a/libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.sentinel/sized_sentinel_for.compile.pass.cpp b/libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.sentinel/sized_sentinel_for.compile.pass.cpp
new file mode 100644
--- /dev/null
+++ b/libcxx/test/std/iterators/iterator.requirements/iterator.concepts/iterator.concept.sentinel/sized_sentinel_for.compile.pass.cpp
@@ -0,0 +1,85 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+// UNSUPPORTED: libcpp-no-concepts
+// UNSUPPORTED: gcc-10
+
+// [iterator.concept.sizedsentinel], concept sized_sentinel_for
+//
+// template<class S, class I>
+//   inline constexpr bool disable_sized_sentinel_for = false;
+//
+// template<class S, class I>
+//   concept sized_sentinel_for = see below;
+
+#include <iterator>
+
+#include <array>
+#include <concepts>
+#include <deque>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "test_iterators.h"
+#include "test_macros.h"
+
+static_assert(std::sized_sentinel_for<random_access_iterator<int*>, random_access_iterator<int*> >);
+static_assert(!std::sized_sentinel_for<bidirectional_iterator<int*>, bidirectional_iterator<int*> >);
+
+struct int_sized_sentinel {
+  friend bool operator==(int_sized_sentinel, int*);
+  friend long operator-(int_sized_sentinel, int*);
+  friend long operator-(int*, int_sized_sentinel);
+};
+static_assert(std::sized_sentinel_for<int_sized_sentinel, int*>);
+// int_sized_sentinel is not an iterator.
+static_assert(!std::sized_sentinel_for<int*, int_sized_sentinel>);
+
+struct no_default_ctor {
+  no_default_ctor() = delete;
+  bool operator==(std::input_or_output_iterator auto) const;
+};
+static_assert(!std::sized_sentinel_for<no_default_ctor, int*>);
+
+struct not_copyable {
+  not_copyable() = default;
+  not_copyable(not_copyable const&) = delete;
+  bool operator==(std::input_or_output_iterator auto) const;
+};
+static_assert(!std::sized_sentinel_for<not_copyable, int*>);
+
+struct double_sized_sentinel {
+  friend bool operator==(double_sized_sentinel, double*);
+  friend int operator-(double_sized_sentinel, double*);
+  friend int operator-(double*, double_sized_sentinel);
+};
+template <>
+inline constexpr bool std::disable_sized_sentinel_for<double_sized_sentinel, double*> = true;
+
+static_assert(!std::sized_sentinel_for<double_sized_sentinel, double*>);
+
+struct only_one_sub_op {
+  friend bool operator==(only_one_sub_op, std::input_or_output_iterator auto);
+  friend long operator-(only_one_sub_op, std::input_or_output_iterator auto);
+};
+static_assert(!std::sized_sentinel_for<only_one_sub_op, int*>);
+
+struct wrong_return_type {
+  friend bool operator==(wrong_return_type, std::input_or_output_iterator auto);
+  friend long operator-(wrong_return_type, std::input_or_output_iterator auto);
+  friend void operator-(std::input_or_output_iterator auto, wrong_return_type);
+};
+static_assert(!std::sized_sentinel_for<wrong_return_type, int*>);
+
+// Standard types
+static_assert(std::sized_sentinel_for<int*, int*>);
+static_assert(std::sized_sentinel_for<const int*, int*>);
+static_assert(std::sized_sentinel_for<const int*, const int*>);
+static_assert(std::sized_sentinel_for<int*, const int*>);
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/back.insert.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -22,3 +22,4 @@
 static_assert(!std::weakly_incrementable<iterator>);
 static_assert(!std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/insert.iterators/front.insert.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -22,3 +22,4 @@
 static_assert(!std::weakly_incrementable<iterator>);
 static_assert(!std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/predef.iterators/move.iterators/move.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/predef.iterators/move.iterators/move.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/predef.iterators/move.iterators/move.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/predef.iterators/move.iterators/move.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -20,3 +20,4 @@
 static_assert(std::incrementable<iterator>);
 static_assert(std::input_or_output_iterator<iterator>);
 static_assert(std::sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/istream.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/istream.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/istream.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/istream.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -22,3 +22,4 @@
 static_assert(std::incrementable<iterator>);
 static_assert(std::input_or_output_iterator<iterator>);
 static_assert(std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/istreambuf.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/istreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/istreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/istreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -24,3 +24,4 @@
 static_assert(!std::incrementable<iterator>);
 static_assert(std::input_or_output_iterator<iterator>);
 static_assert(std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/ostream.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -22,3 +22,4 @@
 static_assert(!std::weakly_incrementable<iterator>);
 static_assert(!std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/iterators/stream.iterators/ostreambuf.iterator/iterator_concept_conformance.compile.pass.cpp
@@ -23,3 +23,4 @@
 static_assert(!std::weakly_incrementable<iterator>);
 static_assert(!std::input_or_output_iterator<iterator>);
 static_assert(!std::sentinel_for<iterator, iterator>);
+static_assert(!std::sized_sentinel_for<iterator, iterator>);
diff --git a/libcxx/test/std/re/re.iter/re.regiter/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/re/re.iter/re.regiter/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/re/re.iter/re.regiter/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/re/re.iter/re.regiter/iterator_concept_conformance.compile.pass.cpp
@@ -21,3 +21,4 @@
 static_assert(std::incrementable<std::cregex_iterator>);
 static_assert(std::input_or_output_iterator<std::cregex_iterator>);
 static_assert(std::sentinel_for<std::cregex_iterator, std::cregex_iterator>);
+static_assert(!std::sized_sentinel_for<std::cregex_iterator, std::cregex_iterator>);
diff --git a/libcxx/test/std/re/re.iter/re.tokiter/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/re/re.iter/re.tokiter/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/re/re.iter/re.tokiter/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/re/re.iter/re.tokiter/iterator_concept_conformance.compile.pass.cpp
@@ -21,3 +21,4 @@
 static_assert(std::incrementable<std::cregex_token_iterator>);
 static_assert(std::input_or_output_iterator<std::cregex_token_iterator>);
 static_assert(std::sentinel_for<std::cregex_token_iterator, std::cregex_token_iterator>);
+static_assert(!std::sized_sentinel_for<std::cregex_token_iterator, std::cregex_token_iterator>);
diff --git a/libcxx/test/std/strings/basic.string/string.iterators/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/strings/basic.string/string.iterators/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/strings/basic.string/string.iterators/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/strings/basic.string/string.iterators/iterator_concept_conformance.compile.pass.cpp
@@ -38,3 +38,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);
diff --git a/libcxx/test/std/strings/string.view/string.view.iterators/iterator_concept_conformance.compile.pass.cpp b/libcxx/test/std/strings/string.view/string.view.iterators/iterator_concept_conformance.compile.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.iterators/iterator_concept_conformance.compile.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.iterators/iterator_concept_conformance.compile.pass.cpp
@@ -38,3 +38,23 @@
 static_assert(std::sentinel_for<const_iterator, const_iterator>);
 static_assert(!std::sentinel_for<const_iterator, reverse_iterator>);
 static_assert(!std::sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(std::sized_sentinel_for<iterator, iterator>);
+static_assert(std::sized_sentinel_for<iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, iterator>);
+static_assert(std::sized_sentinel_for<const_iterator, const_iterator>);
+
+static_assert(!std::sized_sentinel_for<iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<iterator, const_reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, reverse_iterator>);
+static_assert(!std::sized_sentinel_for<const_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<reverse_iterator, const_reverse_iterator>);
+
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, iterator>);
+static_assert(!std::sized_sentinel_for<const_reverse_iterator, const_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, reverse_iterator>);
+static_assert(std::sized_sentinel_for<const_reverse_iterator, const_reverse_iterator>);