diff --git a/libcxx/include/__algorithm/ranges_stable_sort.h b/libcxx/include/__algorithm/ranges_stable_sort.h
index 9c7df80ae9872..6e17d0d0c7ec4 100644
--- a/libcxx/include/__algorithm/ranges_stable_sort.h
+++ b/libcxx/include/__algorithm/ranges_stable_sort.h
@@ -41,7 +41,8 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 namespace ranges {
 struct __stable_sort {
   template <class _Iter, class _Sent, class _Comp, class _Proj>
-  _LIBCPP_HIDE_FROM_ABI static _Iter __stable_sort_fn_impl(_Iter __first, _Sent __last, _Comp& __comp, _Proj& __proj) {
+  _LIBCPP_HIDE_FROM_ABI static _LIBCPP_CONSTEXPR_SINCE_CXX26 _Iter
+  __stable_sort_fn_impl(_Iter __first, _Sent __last, _Comp& __comp, _Proj& __proj) {
     auto __last_iter = ranges::next(__first, __last);
 
     auto&& __projected_comp = std::__make_projected(__comp, __proj);
@@ -52,13 +53,14 @@ struct __stable_sort {
 
   template <random_access_iterator _Iter, sentinel_for<_Iter> _Sent, class _Comp = ranges::less, class _Proj = identity>
     requires sortable<_Iter, _Comp, _Proj>
-  _LIBCPP_HIDE_FROM_ABI _Iter operator()(_Iter __first, _Sent __last, _Comp __comp = {}, _Proj __proj = {}) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 _Iter
+  operator()(_Iter __first, _Sent __last, _Comp __comp = {}, _Proj __proj = {}) const {
     return __stable_sort_fn_impl(std::move(__first), std::move(__last), __comp, __proj);
   }
 
   template <random_access_range _Range, class _Comp = ranges::less, class _Proj = identity>
     requires sortable<iterator_t<_Range>, _Comp, _Proj>
-  _LIBCPP_HIDE_FROM_ABI borrowed_iterator_t<_Range>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 borrowed_iterator_t<_Range>
   operator()(_Range&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
     return __stable_sort_fn_impl(ranges::begin(__r), ranges::end(__r), __comp, __proj);
   }
diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index 0c7cea11d1a91..2ec6582adbfc2 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -422,11 +422,12 @@ namespace ranges {
   template<random_access_iterator I, sentinel_for<I> S, class Comp = ranges::less,
           class Proj = identity>
     requires sortable<I, Comp, Proj>
-    I ranges::stable_sort(I first, S last, Comp comp = {}, Proj proj = {});                 // since C++20
+    constexpr I                                                                             // constexpr since C++26
+      ranges::stable_sort(I first, S last, Comp comp = {}, Proj proj = {});                 // since C++20
 
   template<random_access_range R, class Comp = ranges::less, class Proj = identity>
     requires sortable<iterator_t<R>, Comp, Proj>
-    borrowed_iterator_t<R>
+    constexpr borrowed_iterator_t<R>                                                        // constexpr since C++26
       ranges::stable_sort(R&& r, Comp comp = {}, Proj proj = {});                           // since C++20
 
   template<random_access_iterator I, sentinel_for<I> S, class Comp = ranges::less,
@@ -1165,84 +1166,84 @@ namespace ranges {
 }
 
 template <class InputIterator, class Predicate>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     all_of(InputIterator first, InputIterator last, Predicate pred);
 
 template <class InputIterator, class Predicate>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     any_of(InputIterator first, InputIterator last, Predicate pred);
 
 template <class InputIterator, class Predicate>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     none_of(InputIterator first, InputIterator last, Predicate pred);
 
 template <class InputIterator, class Function>
-    constexpr Function          // constexpr in C++20
+    constexpr Function          // constexpr since C++20
     for_each(InputIterator first, InputIterator last, Function f);
 
 template<class InputIterator, class Size, class Function>
-    constexpr InputIterator     // constexpr in C++20
+    constexpr InputIterator     // constexpr since C++20
     for_each_n(InputIterator first, Size n, Function f); // C++17
 
 template <class InputIterator, class T>
-    constexpr InputIterator     // constexpr in C++20
+    constexpr InputIterator     // constexpr since C++20
     find(InputIterator first, InputIterator last, const T& value);
 
 template <class InputIterator, class Predicate>
-    constexpr InputIterator     // constexpr in C++20
+    constexpr InputIterator     // constexpr since C++20
     find_if(InputIterator first, InputIterator last, Predicate pred);
 
 template<class InputIterator, class Predicate>
-    constexpr InputIterator     // constexpr in C++20
+    constexpr InputIterator     // constexpr since C++20
     find_if_not(InputIterator first, InputIterator last, Predicate pred);
 
 template <class ForwardIterator1, class ForwardIterator2>
-    constexpr ForwardIterator1  // constexpr in C++20
+    constexpr ForwardIterator1  // constexpr since C++20
     find_end(ForwardIterator1 first1, ForwardIterator1 last1,
              ForwardIterator2 first2, ForwardIterator2 last2);
 
 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
-    constexpr ForwardIterator1  // constexpr in C++20
+    constexpr ForwardIterator1  // constexpr since C++20
     find_end(ForwardIterator1 first1, ForwardIterator1 last1,
              ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred);
 
 template <class ForwardIterator1, class ForwardIterator2>
-    constexpr ForwardIterator1  // constexpr in C++20
+    constexpr ForwardIterator1  // constexpr since C++20
     find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
                   ForwardIterator2 first2, ForwardIterator2 last2);
 
 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
-    constexpr ForwardIterator1  // constexpr in C++20
+    constexpr ForwardIterator1  // constexpr since C++20
     find_first_of(ForwardIterator1 first1, ForwardIterator1 last1,
                   ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred);
 
 template <class ForwardIterator>
-    constexpr ForwardIterator   // constexpr in C++20
+    constexpr ForwardIterator   // constexpr since C++20
     adjacent_find(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class BinaryPredicate>
-    constexpr ForwardIterator   // constexpr in C++20
+    constexpr ForwardIterator   // constexpr since C++20
     adjacent_find(ForwardIterator first, ForwardIterator last, BinaryPredicate pred);
 
 template <class InputIterator, class T>
-    constexpr typename iterator_traits<InputIterator>::difference_type  // constexpr in C++20
+    constexpr typename iterator_traits<InputIterator>::difference_type  // constexpr since C++20
     count(InputIterator first, InputIterator last, const T& value);
 
 template <class InputIterator, class Predicate>
-    constexpr typename iterator_traits<InputIterator>::difference_type // constexpr in C++20
+    constexpr typename iterator_traits<InputIterator>::difference_type // constexpr since C++20
     count_if(InputIterator first, InputIterator last, Predicate pred);
 
 template <class InputIterator1, class InputIterator2>
-    constexpr pair<InputIterator1, InputIterator2>   // constexpr in C++20
+    constexpr pair<InputIterator1, InputIterator2>   // constexpr since C++20
     mismatch(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2);
 
 template <class InputIterator1, class InputIterator2>
     constexpr pair<InputIterator1, InputIterator2>
     mismatch(InputIterator1 first1, InputIterator1 last1,
-             InputIterator2 first2, InputIterator2 last2);              // since C++14, constexpr in C++20
+             InputIterator2 first2, InputIterator2 last2);              // since C++14, constexpr since C++20
 
 template <class InputIterator1, class InputIterator2, class BinaryPredicate>
-    constexpr pair<InputIterator1, InputIterator2>   // constexpr in C++20
+    constexpr pair<InputIterator1, InputIterator2>   // constexpr since C++20
     mismatch(InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, BinaryPredicate pred);
 
@@ -1250,19 +1251,19 @@ template <class InputIterator1, class InputIterator2, class BinaryPredicate>
     constexpr pair<InputIterator1, InputIterator2>
     mismatch(InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, InputIterator2 last2,
-             BinaryPredicate pred);                                     // since C++14, constexpr in C++20
+             BinaryPredicate pred);                                     // since C++14, constexpr since C++20
 
 template <class InputIterator1, class InputIterator2>
-    constexpr bool      // constexpr in C++20
+    constexpr bool      // constexpr since C++20
     equal(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2);
 
 template <class InputIterator1, class InputIterator2>
     constexpr bool
     equal(InputIterator1 first1, InputIterator1 last1,
-          InputIterator2 first2, InputIterator2 last2);                 // since C++14, constexpr in C++20
+          InputIterator2 first2, InputIterator2 last2);                 // since C++14, constexpr since C++20
 
 template <class InputIterator1, class InputIterator2, class BinaryPredicate>
-    constexpr bool      // constexpr in C++20
+    constexpr bool      // constexpr since C++20
     equal(InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, BinaryPredicate pred);
 
@@ -1270,20 +1271,20 @@ template <class InputIterator1, class InputIterator2, class BinaryPredicate>
     constexpr bool
     equal(InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, InputIterator2 last2,
-          BinaryPredicate pred);                                        // since C++14, constexpr in C++20
+          BinaryPredicate pred);                                        // since C++14, constexpr since C++20
 
 template<class ForwardIterator1, class ForwardIterator2>
-    constexpr bool      // constexpr in C++20
+    constexpr bool      // constexpr since C++20
     is_permutation(ForwardIterator1 first1, ForwardIterator1 last1,
                    ForwardIterator2 first2);
 
 template<class ForwardIterator1, class ForwardIterator2>
     constexpr bool
     is_permutation(ForwardIterator1 first1, ForwardIterator1 last1,
-                   ForwardIterator2 first2, ForwardIterator2 last2);    // since C++14, constexpr in C++20
+                   ForwardIterator2 first2, ForwardIterator2 last2);    // since C++14, constexpr since C++20
 
 template<class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
-    constexpr bool      // constexpr in C++20
+    constexpr bool      // constexpr since C++20
     is_permutation(ForwardIterator1 first1, ForwardIterator1 last1,
                    ForwardIterator2 first2, BinaryPredicate pred);
 
@@ -1291,42 +1292,42 @@ template<class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
     constexpr bool
     is_permutation(ForwardIterator1 first1, ForwardIterator1 last1,
                    ForwardIterator2 first2, ForwardIterator2 last2,
-                   BinaryPredicate pred);                               // since C++14, constexpr in C++20
+                   BinaryPredicate pred);                               // since C++14, constexpr since C++20
 
 template <class ForwardIterator1, class ForwardIterator2>
-    constexpr ForwardIterator1      // constexpr in C++20
+    constexpr ForwardIterator1      // constexpr since C++20
     search(ForwardIterator1 first1, ForwardIterator1 last1,
            ForwardIterator2 first2, ForwardIterator2 last2);
 
 template <class ForwardIterator1, class ForwardIterator2, class BinaryPredicate>
-    constexpr ForwardIterator1      // constexpr in C++20
+    constexpr ForwardIterator1      // constexpr since C++20
     search(ForwardIterator1 first1, ForwardIterator1 last1,
            ForwardIterator2 first2, ForwardIterator2 last2, BinaryPredicate pred);
 
 template <class ForwardIterator, class Size, class T>
-    constexpr ForwardIterator       // constexpr in C++20
+    constexpr ForwardIterator       // constexpr since C++20
     search_n(ForwardIterator first, ForwardIterator last, Size count, const T& value);
 
 template <class ForwardIterator, class Size, class T, class BinaryPredicate>
-    constexpr ForwardIterator       // constexpr in C++20
+    constexpr ForwardIterator       // constexpr since C++20
     search_n(ForwardIterator first, ForwardIterator last,
              Size count, const T& value, BinaryPredicate pred);
 
 template <class InputIterator, class OutputIterator>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     copy(InputIterator first, InputIterator last, OutputIterator result);
 
 template<class InputIterator, class OutputIterator, class Predicate>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     copy_if(InputIterator first, InputIterator last,
             OutputIterator result, Predicate pred);
 
 template<class InputIterator, class Size, class OutputIterator>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     copy_n(InputIterator first, Size n, OutputIterator result);
 
 template <class BidirectionalIterator1, class BidirectionalIterator2>
-    constexpr BidirectionalIterator2      // constexpr in C++20
+    constexpr BidirectionalIterator2      // constexpr since C++20
     copy_backward(BidirectionalIterator1 first, BidirectionalIterator1 last,
                   BidirectionalIterator2 result);
 
@@ -1341,7 +1342,7 @@ template<class BidirectionalIterator1, class BidirectionalIterator2>
                   BidirectionalIterator2 result);
 
 template <class ForwardIterator1, class ForwardIterator2>
-    constexpr ForwardIterator2    // constexpr in C++20
+    constexpr ForwardIterator2    // constexpr since C++20
     swap_ranges(ForwardIterator1 first1, ForwardIterator1 last1, ForwardIterator2 first2);
 
 namespace ranges {
@@ -1360,97 +1361,97 @@ template<input_range R1, input_range R2>
 }
 
 template <class ForwardIterator1, class ForwardIterator2>
-    constexpr void                // constexpr in C++20
+    constexpr void                // constexpr since C++20
     iter_swap(ForwardIterator1 a, ForwardIterator2 b);
 
 template <class InputIterator, class OutputIterator, class UnaryOperation>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     transform(InputIterator first, InputIterator last, OutputIterator result, UnaryOperation op);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class BinaryOperation>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     transform(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2,
               OutputIterator result, BinaryOperation binary_op);
 
 template <class ForwardIterator, class T>
-    constexpr void      // constexpr in C++20
+    constexpr void      // constexpr since C++20
     replace(ForwardIterator first, ForwardIterator last, const T& old_value, const T& new_value);
 
 template <class ForwardIterator, class Predicate, class T>
-    constexpr void      // constexpr in C++20
+    constexpr void      // constexpr since C++20
     replace_if(ForwardIterator first, ForwardIterator last, Predicate pred, const T& new_value);
 
 template <class InputIterator, class OutputIterator, class T>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     replace_copy(InputIterator first, InputIterator last, OutputIterator result,
                  const T& old_value, const T& new_value);
 
 template <class InputIterator, class OutputIterator, class Predicate, class T>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     replace_copy_if(InputIterator first, InputIterator last, OutputIterator result, Predicate pred, const T& new_value);
 
 template <class ForwardIterator, class T>
-    constexpr void      // constexpr in C++20
+    constexpr void      // constexpr since C++20
     fill(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class OutputIterator, class Size, class T>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     fill_n(OutputIterator first, Size n, const T& value);
 
 template <class ForwardIterator, class Generator>
-    constexpr void      // constexpr in C++20
+    constexpr void      // constexpr since C++20
     generate(ForwardIterator first, ForwardIterator last, Generator gen);
 
 template <class OutputIterator, class Size, class Generator>
-    constexpr OutputIterator      // constexpr in C++20
+    constexpr OutputIterator      // constexpr since C++20
     generate_n(OutputIterator first, Size n, Generator gen);
 
 template <class ForwardIterator, class T>
-    constexpr ForwardIterator     // constexpr in C++20
+    constexpr ForwardIterator     // constexpr since C++20
     remove(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class Predicate>
-    constexpr ForwardIterator     // constexpr in C++20
+    constexpr ForwardIterator     // constexpr since C++20
     remove_if(ForwardIterator first, ForwardIterator last, Predicate pred);
 
 template <class InputIterator, class OutputIterator, class T>
-    constexpr OutputIterator     // constexpr in C++20
+    constexpr OutputIterator     // constexpr since C++20
     remove_copy(InputIterator first, InputIterator last, OutputIterator result, const T& value);
 
 template <class InputIterator, class OutputIterator, class Predicate>
-    constexpr OutputIterator     // constexpr in C++20
+    constexpr OutputIterator     // constexpr since C++20
     remove_copy_if(InputIterator first, InputIterator last, OutputIterator result, Predicate pred);
 
 template <class ForwardIterator>
-    constexpr ForwardIterator    // constexpr in C++20
+    constexpr ForwardIterator    // constexpr since C++20
     unique(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class BinaryPredicate>
-    constexpr ForwardIterator    // constexpr in C++20
+    constexpr ForwardIterator    // constexpr since C++20
     unique(ForwardIterator first, ForwardIterator last, BinaryPredicate pred);
 
 template <class InputIterator, class OutputIterator>
-    constexpr OutputIterator     // constexpr in C++20
+    constexpr OutputIterator     // constexpr since C++20
     unique_copy(InputIterator first, InputIterator last, OutputIterator result);
 
 template <class InputIterator, class OutputIterator, class BinaryPredicate>
-    constexpr OutputIterator     // constexpr in C++20
+    constexpr OutputIterator     // constexpr since C++20
     unique_copy(InputIterator first, InputIterator last, OutputIterator result, BinaryPredicate pred);
 
 template <class BidirectionalIterator>
-    constexpr void               // constexpr in C++20
+    constexpr void               // constexpr since C++20
     reverse(BidirectionalIterator first, BidirectionalIterator last);
 
 template <class BidirectionalIterator, class OutputIterator>
-    constexpr OutputIterator       // constexpr in C++20
+    constexpr OutputIterator       // constexpr since C++20
     reverse_copy(BidirectionalIterator first, BidirectionalIterator last, OutputIterator result);
 
 template <class ForwardIterator>
-    constexpr ForwardIterator      // constexpr in C++20
+    constexpr ForwardIterator      // constexpr since C++20
     rotate(ForwardIterator first, ForwardIterator middle, ForwardIterator last);
 
 template <class ForwardIterator, class OutputIterator>
-    constexpr OutputIterator       // constexpr in C++20
+    constexpr OutputIterator       // constexpr since C++20
     rotate_copy(ForwardIterator first, ForwardIterator middle, ForwardIterator last, OutputIterator result);
 
 template <class RandomAccessIterator>
@@ -1483,125 +1484,125 @@ template<class ForwardIterator>
                 typename iterator_traits<ForwardIterator>::difference_type n); // C++20
 
 template <class InputIterator, class Predicate>
-    constexpr bool  // constexpr in C++20
+    constexpr bool  // constexpr since C++20
     is_partitioned(InputIterator first, InputIterator last, Predicate pred);
 
 template <class ForwardIterator, class Predicate>
-    constexpr ForwardIterator  // constexpr in C++20
+    constexpr ForwardIterator  // constexpr since C++20
     partition(ForwardIterator first, ForwardIterator last, Predicate pred);
 
 template <class InputIterator, class OutputIterator1,
           class OutputIterator2, class Predicate>
-    constexpr pair<OutputIterator1, OutputIterator2>   // constexpr in C++20
+    constexpr pair<OutputIterator1, OutputIterator2>   // constexpr since C++20
     partition_copy(InputIterator first, InputIterator last,
                    OutputIterator1 out_true, OutputIterator2 out_false,
                    Predicate pred);
 
 template <class ForwardIterator, class Predicate>
-    constexpr ForwardIterator                          // constexpr in C++26
+    constexpr ForwardIterator                          // constexpr since C++26
     stable_partition(ForwardIterator first, ForwardIterator last, Predicate pred);
 
 template<class ForwardIterator, class Predicate>
-    constexpr ForwardIterator  // constexpr in C++20
+    constexpr ForwardIterator  // constexpr since C++20
     partition_point(ForwardIterator first, ForwardIterator last, Predicate pred);
 
 template <class ForwardIterator>
-    constexpr bool  // constexpr in C++20
+    constexpr bool  // constexpr since C++20
     is_sorted(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class Compare>
-    constexpr bool  // constexpr in C++20
+    constexpr bool  // constexpr since C++20
     is_sorted(ForwardIterator first, ForwardIterator last, Compare comp);
 
 template<class ForwardIterator>
-    constexpr ForwardIterator    // constexpr in C++20
+    constexpr ForwardIterator    // constexpr since C++20
     is_sorted_until(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class Compare>
-    constexpr ForwardIterator    // constexpr in C++20
+    constexpr ForwardIterator    // constexpr since C++20
     is_sorted_until(ForwardIterator first, ForwardIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void               // constexpr in C++20
+    constexpr void               // constexpr since C++20
     sort(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void               // constexpr in C++20
+    constexpr void               // constexpr since C++20
     sort(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void               // constexpr in C++26
+    constexpr void               // constexpr since C++26
     stable_sort(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void               // constexpr in C++26
+    constexpr void               // constexpr since C++26
     stable_sort(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                    // constexpr in C++20
+    constexpr void                    // constexpr since C++20
     partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                    // constexpr in C++20
+    constexpr void                    // constexpr since C++20
     partial_sort(RandomAccessIterator first, RandomAccessIterator middle, RandomAccessIterator last, Compare comp);
 
 template <class InputIterator, class RandomAccessIterator>
-    constexpr RandomAccessIterator    // constexpr in C++20
+    constexpr RandomAccessIterator    // constexpr since C++20
     partial_sort_copy(InputIterator first, InputIterator last,
                       RandomAccessIterator result_first, RandomAccessIterator result_last);
 
 template <class InputIterator, class RandomAccessIterator, class Compare>
-    constexpr RandomAccessIterator    // constexpr in C++20
+    constexpr RandomAccessIterator    // constexpr since C++20
     partial_sort_copy(InputIterator first, InputIterator last,
                       RandomAccessIterator result_first, RandomAccessIterator result_last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                    // constexpr in C++20
+    constexpr void                    // constexpr since C++20
     nth_element(RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                    // constexpr in C++20
+    constexpr void                    // constexpr since C++20
     nth_element(RandomAccessIterator first, RandomAccessIterator nth, RandomAccessIterator last, Compare comp);
 
 template <class ForwardIterator, class T>
-    constexpr ForwardIterator                         // constexpr in C++20
+    constexpr ForwardIterator                         // constexpr since C++20
     lower_bound(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class T, class Compare>
-    constexpr ForwardIterator                         // constexpr in C++20
+    constexpr ForwardIterator                         // constexpr since C++20
     lower_bound(ForwardIterator first, ForwardIterator last, const T& value, Compare comp);
 
 template <class ForwardIterator, class T>
-    constexpr ForwardIterator                         // constexpr in C++20
+    constexpr ForwardIterator                         // constexpr since C++20
     upper_bound(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class T, class Compare>
-    constexpr ForwardIterator                         // constexpr in C++20
+    constexpr ForwardIterator                         // constexpr since C++20
     upper_bound(ForwardIterator first, ForwardIterator last, const T& value, Compare comp);
 
 template <class ForwardIterator, class T>
-    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr in C++20
+    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr since C++20
     equal_range(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class T, class Compare>
-    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr in C++20
+    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr since C++20
     equal_range(ForwardIterator first, ForwardIterator last, const T& value, Compare comp);
 
 template <class ForwardIterator, class T>
-    constexpr bool                                    // constexpr in C++20
+    constexpr bool                                    // constexpr since C++20
     binary_search(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class T, class Compare>
-    constexpr bool                                    // constexpr in C++20
+    constexpr bool                                    // constexpr since C++20
     binary_search(ForwardIterator first, ForwardIterator last, const T& value, Compare comp);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator>
-    constexpr OutputIterator                          // constexpr in C++20
+    constexpr OutputIterator                          // constexpr since C++20
     merge(InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, InputIterator2 last2, OutputIterator result);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class Compare>
-    constexpr OutputIterator                          // constexpr in C++20
+    constexpr OutputIterator                          // constexpr since C++20
     merge(InputIterator1 first1, InputIterator1 last1,
           InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);
 
@@ -1614,123 +1615,123 @@ template <class BidirectionalIterator, class Compare>
     inplace_merge(BidirectionalIterator first, BidirectionalIterator middle, BidirectionalIterator last, Compare comp);
 
 template <class InputIterator1, class InputIterator2>
-    constexpr bool                                    // constexpr in C++20
+    constexpr bool                                    // constexpr since C++20
     includes(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2);
 
 template <class InputIterator1, class InputIterator2, class Compare>
-    constexpr bool                                    // constexpr in C++20
+    constexpr bool                                    // constexpr since C++20
     includes(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2, Compare comp);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator>
-    constexpr OutputIterator                          // constexpr in C++20
+    constexpr OutputIterator                          // constexpr since C++20
     set_union(InputIterator1 first1, InputIterator1 last1,
               InputIterator2 first2, InputIterator2 last2, OutputIterator result);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class Compare>
-    constexpr OutputIterator                          // constexpr in C++20
+    constexpr OutputIterator                          // constexpr since C++20
     set_union(InputIterator1 first1, InputIterator1 last1,
               InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_intersection(InputIterator1 first1, InputIterator1 last1,
                      InputIterator2 first2, InputIterator2 last2, OutputIterator result);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class Compare>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_intersection(InputIterator1 first1, InputIterator1 last1,
                      InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_difference(InputIterator1 first1, InputIterator1 last1,
                    InputIterator2 first2, InputIterator2 last2, OutputIterator result);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class Compare>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_difference(InputIterator1 first1, InputIterator1 last1,
                    InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_symmetric_difference(InputIterator1 first1, InputIterator1 last1,
                              InputIterator2 first2, InputIterator2 last2, OutputIterator result);
 
 template <class InputIterator1, class InputIterator2, class OutputIterator, class Compare>
-    constexpr OutputIterator                         // constexpr in C++20
+    constexpr OutputIterator                         // constexpr since C++20
     set_symmetric_difference(InputIterator1 first1, InputIterator1 last1,
                              InputIterator2 first2, InputIterator2 last2, OutputIterator result, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     push_heap(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     push_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     pop_heap(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     pop_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     make_heap(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     make_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     sort_heap(RandomAccessIterator first, RandomAccessIterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr void                                   // constexpr in C++20
+    constexpr void                                   // constexpr since C++20
     sort_heap(RandomAccessIterator first, RandomAccessIterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr bool   // constexpr in C++20
+    constexpr bool   // constexpr since C++20
     is_heap(RandomAccessIterator first, RandomAccessiterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr bool   // constexpr in C++20
+    constexpr bool   // constexpr since C++20
     is_heap(RandomAccessIterator first, RandomAccessiterator last, Compare comp);
 
 template <class RandomAccessIterator>
-    constexpr RandomAccessIterator   // constexpr in C++20
+    constexpr RandomAccessIterator   // constexpr since C++20
     is_heap_until(RandomAccessIterator first, RandomAccessiterator last);
 
 template <class RandomAccessIterator, class Compare>
-    constexpr RandomAccessIterator   // constexpr in C++20
+    constexpr RandomAccessIterator   // constexpr since C++20
     is_heap_until(RandomAccessIterator first, RandomAccessiterator last, Compare comp);
 
 template <class ForwardIterator>
-    constexpr ForwardIterator        // constexpr in C++14
+    constexpr ForwardIterator        // constexpr since C++14
     min_element(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class Compare>
-    constexpr ForwardIterator        // constexpr in C++14
+    constexpr ForwardIterator        // constexpr since C++14
     min_element(ForwardIterator first, ForwardIterator last, Compare comp);
 
 template <class T>
-    constexpr const T&               // constexpr in C++14
+    constexpr const T&               // constexpr since C++14
     min(const T& a, const T& b);
 
 template <class T, class Compare>
-    constexpr const T&               // constexpr in C++14
+    constexpr const T&               // constexpr since C++14
     min(const T& a, const T& b, Compare comp);
 
 template<class T>
-    constexpr T                      // constexpr in C++14
+    constexpr T                      // constexpr since C++14
     min(initializer_list<T> t);
 
 template<class T, class Compare>
-    constexpr T                      // constexpr in C++14
+    constexpr T                      // constexpr since C++14
     min(initializer_list<T> t, Compare comp);
 
 template<class T>
@@ -1740,59 +1741,59 @@ template<class T, class Compare>
     constexpr const T& clamp(const T& v, const T& lo, const T& hi, Compare comp); // C++17
 
 template <class ForwardIterator>
-    constexpr ForwardIterator        // constexpr in C++14
+    constexpr ForwardIterator        // constexpr since C++14
     max_element(ForwardIterator first, ForwardIterator last);
 
 template <class ForwardIterator, class Compare>
-    constexpr ForwardIterator        // constexpr in C++14
+    constexpr ForwardIterator        // constexpr since C++14
     max_element(ForwardIterator first, ForwardIterator last, Compare comp);
 
 template <class T>
-    constexpr const T&               // constexpr in C++14
+    constexpr const T&               // constexpr since C++14
     max(const T& a, const T& b);
 
 template <class T, class Compare>
-    constexpr const T&               // constexpr in C++14
+    constexpr const T&               // constexpr since C++14
     max(const T& a, const T& b, Compare comp);
 
 template<class T>
-    constexpr T                      // constexpr in C++14
+    constexpr T                      // constexpr since C++14
     max(initializer_list<T> t);
 
 template<class T, class Compare>
-    constexpr T                      // constexpr in C++14
+    constexpr T                      // constexpr since C++14
     max(initializer_list<T> t, Compare comp);
 
 template<class ForwardIterator>
-    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr in C++14
+    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr since C++14
     minmax_element(ForwardIterator first, ForwardIterator last);
 
 template<class ForwardIterator, class Compare>
-    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr in C++14
+    constexpr pair<ForwardIterator, ForwardIterator>  // constexpr since C++14
     minmax_element(ForwardIterator first, ForwardIterator last, Compare comp);
 
 template<class T>
-    constexpr pair<const T&, const T&>  // constexpr in C++14
+    constexpr pair<const T&, const T&>  // constexpr since C++14
     minmax(const T& a, const T& b);
 
 template<class T, class Compare>
-    constexpr pair<const T&, const T&>  // constexpr in C++14
+    constexpr pair<const T&, const T&>  // constexpr since C++14
     minmax(const T& a, const T& b, Compare comp);
 
 template<class T>
-    constexpr pair<T, T>                // constexpr in C++14
+    constexpr pair<T, T>                // constexpr since C++14
     minmax(initializer_list<T> t);
 
 template<class T, class Compare>
-    constexpr pair<T, T>                // constexpr in C++14
+    constexpr pair<T, T>                // constexpr since C++14
     minmax(initializer_list<T> t, Compare comp);
 
 template <class InputIterator1, class InputIterator2>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     lexicographical_compare(InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, InputIterator2 last2);
 
 template <class InputIterator1, class InputIterator2, class Compare>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
                             InputIterator2 first2, InputIterator2 last2, Compare comp);
 
@@ -1809,19 +1810,19 @@ template<class InputIterator1, class InputIterator2>
                                       InputIterator2 first2, InputIterator2 last2);      // since C++20
 
 template <class BidirectionalIterator>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     next_permutation(BidirectionalIterator first, BidirectionalIterator last);
 
 template <class BidirectionalIterator, class Compare>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     next_permutation(BidirectionalIterator first, BidirectionalIterator last, Compare comp);
 
 template <class BidirectionalIterator>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     prev_permutation(BidirectionalIterator first, BidirectionalIterator last);
 
 template <class BidirectionalIterator, class Compare>
-    constexpr bool     // constexpr in C++20
+    constexpr bool     // constexpr since C++20
     prev_permutation(BidirectionalIterator first, BidirectionalIterator last, Compare comp);
 }  // std
 
diff --git a/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/ranges.stable.sort.pass.cpp b/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/ranges.stable.sort.pass.cpp
index c8f76b20c6825..10e0874b3bc83 100644
--- a/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/ranges.stable.sort.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.sorting/alg.sort/stable.sort/ranges.stable.sort.pass.cpp
@@ -13,11 +13,12 @@
 // template<random_access_iterator I, sentinel_for<I> S, class Comp = ranges::less,
 //         class Proj = identity>
 //   requires sortable<I, Comp, Proj>
-//   I ranges::stable_sort(I first, S last, Comp comp = {}, Proj proj = {});                 // since C++20
+//   constexpr I                                                                             // constexpr since C++26
+//     ranges::stable_sort(I first, S last, Comp comp = {}, Proj proj = {});                 // since C++20
 //
 // template<random_access_range R, class Comp = ranges::less, class Proj = identity>
 //   requires sortable<iterator_t<R>, Comp, Proj>
-//   borrowed_iterator_t<R>
+//   constexpr borrowed_iterator_t<R>                                                        // constexpr since C++26
 //     ranges::stable_sort(R&& r, Comp comp = {}, Proj proj = {});                           // since C++20
 
 #include <algorithm>
@@ -57,7 +58,7 @@ static_assert(!HasStableSortR<UncheckedRange<int*>, BadComparator>);
 static_assert(!HasStableSortR<UncheckedRange<const int*>>); // Doesn't satisfy `sortable`.
 
 template <class Iter, class Sent, std::size_t N>
-void test_one(std::array<int, N> input, std::array<int, N> expected) {
+TEST_CONSTEXPR_CXX26 void test_one(std::array<int, N> input, std::array<int, N> expected) {
   { // (iterator, sentinel) overload.
     auto sorted = input;
     auto b = Iter(sorted.data());
@@ -81,7 +82,7 @@ void test_one(std::array<int, N> input, std::array<int, N> expected) {
 }
 
 template <class Iter, class Sent>
-void test_iterators_2() {
+TEST_CONSTEXPR_CXX26 void test_iterators_2() {
   // Empty sequence.
   test_one<Iter, Sent, 0>({}, {});
   // 1-element sequence.
@@ -105,25 +106,25 @@ void test_iterators_2() {
 }
 
 template <class Iter>
-void test_iterators_1() {
+TEST_CONSTEXPR_CXX26 void test_iterators_1() {
   test_iterators_2<Iter, Iter>();
   test_iterators_2<Iter, sentinel_wrapper<Iter>>();
 }
 
-void test_iterators() {
+TEST_CONSTEXPR_CXX26 void test_iterators() {
   test_iterators_1<random_access_iterator<int*>>();
   test_iterators_1<contiguous_iterator<int*>>();
   test_iterators_1<int*>();
 }
 
-void test() {
+TEST_CONSTEXPR_CXX26 bool test() {
   test_iterators();
 
   struct OrderedValue {
     int value;
     double original_order;
     bool operator==(const OrderedValue&) const = default;
-    auto operator<=>(const OrderedValue& rhs) const { return value <=> rhs.value; }
+    TEST_CONSTEXPR_CXX26 auto operator<=>(const OrderedValue& rhs) const { return value <=> rhs.value; }
   };
 
   { // The sort is stable (equivalent elements remain in the same order).
@@ -214,10 +215,10 @@ void test() {
   { // `std::invoke` is used in the implementation.
     struct S {
       int i;
-      S(int i_) : i(i_) {}
+      TEST_CONSTEXPR_CXX26 S(int i_) : i(i_) {}
 
-      bool comparator(const S& rhs) const { return i < rhs.i; }
-      const S& projection() const { return *this; }
+      TEST_CONSTEXPR_CXX26 bool comparator(const S& rhs) const { return i < rhs.i; }
+      TEST_CONSTEXPR_CXX26 const S& projection() const { return *this; }
 
       bool operator==(const S&) const = default;
     };
@@ -242,8 +243,6 @@ void test() {
         std::ranges::stable_sort(std::array{1, 2, 3});
   }
 
-  // TODO: Enable the tests once the implementation switched to use iter_move/iter_swap
-  /*
   { // ProxyIterator
     {
       std::array in = {2, 1, 3};
@@ -260,12 +259,15 @@ void test() {
       assert((in == std::array{1, 2, 3}));
     }
   }
-  */
+
+  return true;
 }
 
 int main(int, char**) {
   test();
-  // Note: `stable_sort` is not `constexpr`.
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
index 0624a6c2d49c7..299478da22072 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_dangling.pass.cpp
@@ -200,8 +200,12 @@ constexpr bool test_all() {
   if (!std::is_constant_evaluated())
     dangling_1st(std::ranges::stable_partition, in, unary_pred);
   dangling_1st(std::ranges::sort, in);
+#if TEST_STD_VER < 26
   if (!std::is_constant_evaluated())
+#endif
+  {
     dangling_1st(std::ranges::stable_sort, in);
+  }
   dangling_1st(std::ranges::partial_sort, in, mid);
   dangling_1st(std::ranges::nth_element, in, mid);
   if (!std::is_constant_evaluated())
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
index acd7640b418eb..a01cdf1d3a179 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_omitting_invoke.pass.cpp
@@ -167,8 +167,12 @@ constexpr bool test_all() {
   if (!std::is_constant_evaluated())
     test(std::ranges::stable_partition, in, &Foo::unary_pred, &Bar::val);
   test(std::ranges::sort, in, &Foo::binary_pred, &Bar::val);
+#if TEST_STD_VER < 26
   if (!std::is_constant_evaluated())
+#endif
+  {
     test(std::ranges::stable_sort, in, &Foo::binary_pred, &Bar::val);
+  }
   test_mid(std::ranges::partial_sort, in, mid, &Foo::binary_pred, &Bar::val);
   test_mid(std::ranges::nth_element, in, mid, &Foo::binary_pred, &Bar::val);
   if (!std::is_constant_evaluated())
diff --git a/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp b/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
index ca1433b778751..d85052c51973a 100644
--- a/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
+++ b/libcxx/test/std/algorithms/ranges_robust_against_proxy_iterators.pass.cpp
@@ -170,8 +170,12 @@ constexpr void run_tests() {
   if (!std::is_constant_evaluated())
     test(std::ranges::stable_partition, in, unary_pred);
   test(std::ranges::sort, in);
+#if TEST_STD_VER < 26
   if (!std::is_constant_evaluated())
+#endif
+  {
     test(std::ranges::stable_sort, in);
+  }
   test_mid(std::ranges::partial_sort, in, mid);
   test_mid(std::ranges::nth_element, in, mid);
   if (!std::is_constant_evaluated())
diff --git a/libcxx/test/support/test_iterators.h b/libcxx/test/support/test_iterators.h
index 419f1d86730b8..ead8a3e8f87d2 100644
--- a/libcxx/test/support/test_iterators.h
+++ b/libcxx/test/support/test_iterators.h
@@ -1208,6 +1208,10 @@ struct Proxy {
 
   constexpr const T&& getData() const&& { return static_cast<const T&&>(data); }
 
+  // Explicitly declare the copy constructor as defaulted to avoid deprecation of the implicitly declared one
+  // because of the user-provided copy assignment operator.
+  Proxy(const Proxy&) = default;
+
   template <class U>
     requires std::constructible_from<T, U&&>
   constexpr Proxy(U&& u) : data{std::forward<U>(u)} {}