diff --git a/libcxx/include/__config b/libcxx/include/__config
index ce8bc38acfe3e..026e77b8a4b72 100644
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1213,14 +1213,6 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_DIAGNOSE_NULLPTR
 #  endif
 
-// TODO(LLVM 22): Remove this macro once LLVM19 support ends. __cpp_explicit_this_parameter has been set in LLVM20.
-// Clang-18 has support for deducing this, but it does not set the FTM.
-#  if defined(__cpp_explicit_this_parameter) || (defined(_LIBCPP_CLANG_VER) && _LIBCPP_CLANG_VER >= 1800)
-#    define _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER 1
-#  else
-#    define _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER 0
-#  endif
-
 #endif // __cplusplus
 
 #endif // _LIBCPP___CONFIG
diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
index 10f0ba9928ce7..a423924803130 100644
--- a/libcxx/include/__format/format_arg.h
+++ b/libcxx/include/__format/format_arg.h
@@ -149,7 +149,7 @@ _LIBCPP_HIDE_FROM_ABI decltype(auto) __visit_format_arg(_Visitor&& __vis, basic_
   __libcpp_unreachable();
 }
 
-#  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  if _LIBCPP_STD_VER >= 26
 
 template <class _Rp, class _Visitor, class _Context>
 _LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<_Context> __arg) {
@@ -200,7 +200,7 @@ _LIBCPP_HIDE_FROM_ABI _Rp __visit_format_arg(_Visitor&& __vis, basic_format_arg<
   __libcpp_unreachable();
 }
 
-#  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  endif // _LIBCPP_STD_VER >= 26
 
 /// Contains the values used in basic_format_arg.
 ///
@@ -285,7 +285,7 @@ class _LIBCPP_TEMPLATE_VIS _LIBCPP_NO_SPECIALIZATIONS basic_format_arg {
 
   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const noexcept { return __type_ != __format::__arg_t::__none; }
 
-#  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  if _LIBCPP_STD_VER >= 26
 
   // This function is user facing, so it must wrap the non-standard types of
   // the "variant" in a handle to stay conforming. See __arg_t for more details.
@@ -329,7 +329,7 @@ class _LIBCPP_TEMPLATE_VIS _LIBCPP_NO_SPECIALIZATIONS basic_format_arg {
     }
   }
 
-#  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  endif // _LIBCPP_STD_VER >= 26
 
 private:
   using char_type = typename _Context::char_type;
@@ -371,7 +371,7 @@ class _LIBCPP_TEMPLATE_VIS basic_format_arg<_Context>::handle {
 // This function is user facing, so it must wrap the non-standard types of
 // the "variant" in a handle to stay conforming. See __arg_t for more details.
 template <class _Visitor, class _Context>
-#  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  if _LIBCPP_STD_VER >= 26
 _LIBCPP_DEPRECATED_IN_CXX26
 #  endif
     _LIBCPP_HIDE_FROM_ABI decltype(auto)
@@ -387,7 +387,7 @@ _LIBCPP_DEPRECATED_IN_CXX26
     typename __basic_format_arg_value<_Context>::__handle __h{__arg.__value_.__u128_};
     return std::invoke(std::forward<_Visitor>(__vis), typename basic_format_arg<_Context>::handle{__h});
   }
-#  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  endif // _LIBCPP_STD_VER >= 26
   default:
     return std::__visit_format_arg(std::forward<_Visitor>(__vis), __arg);
   }
diff --git a/libcxx/include/__format/format_context.h b/libcxx/include/__format/format_context.h
index 4dbfdbc02a267..45388d6757361 100644
--- a/libcxx/include/__format/format_context.h
+++ b/libcxx/include/__format/format_context.h
@@ -180,13 +180,13 @@ class _LIBCPP_TEMPLATE_VIS basic_format_context<typename __format::__retarget_bu
                   __format::__determine_arg_t<basic_format_context, decltype(__arg)>(),
                   __basic_format_arg_value<basic_format_context>(__arg)};
           };
-#  if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  if _LIBCPP_STD_VER >= 26
           return static_cast<_Context*>(__c)->arg(__id).visit(std::move(__visitor));
 #  else
           _LIBCPP_SUPPRESS_DEPRECATED_PUSH
           return std::visit_format_arg(std::move(__visitor), static_cast<_Context*>(__c)->arg(__id));
           _LIBCPP_SUPPRESS_DEPRECATED_POP
-#  endif // _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#  endif // _LIBCPP_STD_VER >= 26
         }) {
   }
 
diff --git a/libcxx/include/variant b/libcxx/include/variant
index 1c3d1cdc5638e..ab028115e93aa 100644
--- a/libcxx/include/variant
+++ b/libcxx/include/variant
@@ -1302,7 +1302,7 @@ public:
     __impl_.__swap(__that.__impl_);
   }
 
-#    if _LIBCPP_STD_VER >= 26 && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
+#    if _LIBCPP_STD_VER >= 26
   // Helper class to implement [variant.visit]/10
   //   Constraints: The call to visit does not use an explicit template-argument-list
   //   that begins with a type template-argument.
@@ -1319,7 +1319,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI constexpr _Rp visit(this _Self&& __self, _Visitor&& __visitor) {
     return std::visit<_Rp>(std::forward<_Visitor>(__visitor), std::__forward_as<_Self, variant>(__self));
   }
-#    endif
+#    endif // _LIBCPP_STD_VER >= 26
 
 private:
   __variant_detail::__impl<_Types...> __impl_;
diff --git a/libcxx/test/libcxx/algorithms/vectorization.compile.pass.cpp b/libcxx/test/libcxx/algorithms/vectorization.compile.pass.cpp
index 733a147b80cc3..872c49a35dd76 100644
--- a/libcxx/test/libcxx/algorithms/vectorization.compile.pass.cpp
+++ b/libcxx/test/libcxx/algorithms/vectorization.compile.pass.cpp
@@ -17,9 +17,6 @@
 // We don't vectorize algorithms on AIX right now.
 // XFAIL: target={{.+}}-aix{{.*}}
 
-// We don't vectorize on AppleClang 15 since that apparently breaks std::mismatch
-// XFAIL: apple-clang-15
-
 // This test ensures that we enable the vectorization of algorithms on the expected
 // platforms.
 
diff --git a/libcxx/test/libcxx/fuzzing/random.pass.cpp b/libcxx/test/libcxx/fuzzing/random.pass.cpp
index cb074bd60fdc8..e13f48a44dc77 100644
--- a/libcxx/test/libcxx/fuzzing/random.pass.cpp
+++ b/libcxx/test/libcxx/fuzzing/random.pass.cpp
@@ -8,7 +8,7 @@
 
 // This test fails because Clang no longer enables -fdelayed-template-parsing
 // by default on Windows with C++20 (#69431).
-// XFAIL: msvc && (clang-18 || clang-19 || clang-20 || clang-21)
+// XFAIL: msvc && (clang-19 || clang-20 || clang-21)
 
 // UNSUPPORTED: c++03, c++11
 
diff --git a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
index dcdce261298c1..e4ef0c1173ee4 100644
--- a/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
+++ b/libcxx/test/libcxx/gdb/gdb_pretty_printer_test.sh.cpp
@@ -12,7 +12,7 @@
 // UNSUPPORTED: c++03
 
 // TODO: Investigate these failures which break the CI.
-// UNSUPPORTED: clang-18, clang-19, clang-20, clang-21
+// UNSUPPORTED: clang-19, clang-20, clang-21
 
 // The Android libc++ tests are run on a non-Android host, connected to an
 // Android device over adb. gdb needs special support to make this work (e.g.
diff --git a/libcxx/test/libcxx/memory/shared_ptr_array.pass.cpp b/libcxx/test/libcxx/memory/shared_ptr_array.pass.cpp
index cc8c743830826..79f7c14ca3593 100644
--- a/libcxx/test/libcxx/memory/shared_ptr_array.pass.cpp
+++ b/libcxx/test/libcxx/memory/shared_ptr_array.pass.cpp
@@ -10,10 +10,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
 // These compiler versions and platforms don't enable sized deallocation by default.
-// ADDITIONAL_COMPILE_FLAGS(clang-17): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(clang-18): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-15): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-16): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=x86_64-w64-windows-gnu): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=i686-w64-windows-gnu): -fsized-deallocation
 
diff --git a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_add.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_add.pass.cpp
index b162c2da4f337..1b426959475a5 100644
--- a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_add.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_add.pass.cpp
@@ -8,10 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // XFAIL: !has-64-bit-atomics
 
-// Older versions of clang have a bug with atomic builtins affecting double and long double.
-// Fixed by 5fdd0948.
-// XFAIL: target=powerpc-ibm-{{.*}} && clang-18
-
 // https://github.com/llvm/llvm-project/issues/72893
 // XFAIL: target={{x86_64-.*}} && tsan
 
diff --git a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_sub.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_sub.pass.cpp
index 8784037aa5e82..cac7352646fa4 100644
--- a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_sub.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/fetch_sub.pass.cpp
@@ -8,10 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // XFAIL: !has-64-bit-atomics
 
-// Older versions of clang have a bug with atomic builtins affecting double and long double.
-// Fixed by 5fdd0948.
-// XFAIL: target=powerpc-ibm-{{.*}} && clang-18
-
 // https://github.com/llvm/llvm-project/issues/72893
 // XFAIL: target={{x86_64-.*}} && tsan
 
diff --git a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.minus_equals.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.minus_equals.pass.cpp
index e0e079436075f..d38a2d2ed197a 100644
--- a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.minus_equals.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.minus_equals.pass.cpp
@@ -8,10 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // XFAIL: !has-64-bit-atomics
 
-// Older versions of clang have a bug with atomic builtins affecting double and long double.
-// Fixed by 5fdd0948.
-// XFAIL: target=powerpc-ibm-{{.*}} && clang-18
-
 // floating-point-type operator-=(floating-point-type) volatile noexcept;
 // floating-point-type operator-=(floating-point-type) noexcept;
 
diff --git a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.plus_equals.pass.cpp b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.plus_equals.pass.cpp
index 7e2c10106e9ab..c53b0320036bf 100644
--- a/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.plus_equals.pass.cpp
+++ b/libcxx/test/std/atomics/atomics.types.generic/atomics.types.float/operator.plus_equals.pass.cpp
@@ -8,10 +8,6 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 // XFAIL: !has-64-bit-atomics
 
-// Older versions of clang have a bug with atomic builtins affecting double and long double.
-// Fixed by 5fdd0948.
-// XFAIL: target=powerpc-ibm-{{.*}} && clang-18
-
 // floating-point-type operator+=(floating-point-type) volatile noexcept;
 // floating-point-type operator+=(floating-point-type) noexcept;
 
diff --git a/libcxx/test/std/depr/depr.c.headers/math_h.pass.cpp b/libcxx/test/std/depr/depr.c.headers/math_h.pass.cpp
index 1ba0063c1dada..205f5e1af3012 100644
--- a/libcxx/test/std/depr/depr.c.headers/math_h.pass.cpp
+++ b/libcxx/test/std/depr/depr.c.headers/math_h.pass.cpp
@@ -8,7 +8,7 @@
 
 // This test fails because Clang no longer enables -fdelayed-template-parsing
 // by default on Windows with C++20 (#69431).
-// XFAIL: msvc && (clang-18 || clang-19 || clang-20 || clang-21)
+// XFAIL: msvc && (clang-19 || clang-20 || clang-21)
 
 // <math.h>
 
diff --git a/libcxx/test/std/experimental/simd/simd.class/simd_copy.pass.cpp b/libcxx/test/std/experimental/simd/simd.class/simd_copy.pass.cpp
index 6929831eca361..172c97f30c24a 100644
--- a/libcxx/test/std/experimental/simd/simd.class/simd_copy.pass.cpp
+++ b/libcxx/test/std/experimental/simd/simd.class/simd_copy.pass.cpp
@@ -8,10 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14
 
-// Older versions of clang may encounter a backend error (see 0295c2ad):
-//   Pass-by-value arguments with alignment greater than register width are not supported.
-// XFAIL: target=powerpc{{.*}}-ibm-{{.*}} && clang-18
-
 // <experimental/simd>
 //
 // [simd.class]
diff --git a/libcxx/test/std/experimental/simd/simd.class/simd_unary.pass.cpp b/libcxx/test/std/experimental/simd/simd.class/simd_unary.pass.cpp
index eb88d90ca18bd..056d6f65fc368 100644
--- a/libcxx/test/std/experimental/simd/simd.class/simd_unary.pass.cpp
+++ b/libcxx/test/std/experimental/simd/simd.class/simd_unary.pass.cpp
@@ -8,13 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14
 
-// Older versions of clang may encounter a backend error (see 0295c2ad):
-//   Pass-by-value arguments with alignment greater than register width are not supported.
-// XFAIL: target=powerpc{{.*}}-ibm-{{.*}} && clang-18
-
-// This test crashes AppleClang 15 but not later versions.
-// UNSUPPORTED: apple-clang-15
-
 // FIXME: The following issue occurs on Windows to Armv7 Ubuntu Linux:
 //   Assertion failed: N->getValueType(0) == MVT::v1i1 && "Expected v1i1 type"
 // XFAIL: target=armv7-unknown-linux-gnueabihf
diff --git a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array.pass.cpp b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array.pass.cpp
index 01387feed67b6..1d2b938070920 100644
--- a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array.pass.cpp
+++ b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.array/sized_delete_array.pass.cpp
@@ -11,9 +11,6 @@
 // UNSUPPORTED: c++03, c++11
 
 // These compiler versions and platforms don't enable sized deallocation by default.
-// ADDITIONAL_COMPILE_FLAGS(clang-18): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-15): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-16): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(apple-clang-17): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=x86_64-w64-windows-gnu): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=i686-w64-windows-gnu): -fsized-deallocation
diff --git a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete.pass.cpp b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete.pass.cpp
index 06d3b0e5b3c35..551bb4d160270 100644
--- a/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete.pass.cpp
+++ b/libcxx/test/std/language.support/support.dynamic/new.delete/new.delete.single/sized_delete.pass.cpp
@@ -11,9 +11,6 @@
 // UNSUPPORTED: c++03, c++11
 
 // These compiler versions and platforms don't enable sized deallocation by default.
-// ADDITIONAL_COMPILE_FLAGS(clang-18): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-15): -fsized-deallocation
-// ADDITIONAL_COMPILE_FLAGS(apple-clang-16): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(apple-clang-17): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=x86_64-w64-windows-gnu): -fsized-deallocation
 // ADDITIONAL_COMPILE_FLAGS(target=i686-w64-windows-gnu): -fsized-deallocation
diff --git a/libcxx/test/std/numerics/c.math/cmath.pass.cpp b/libcxx/test/std/numerics/c.math/cmath.pass.cpp
index 48c2918802fc3..6a203f1709e05 100644
--- a/libcxx/test/std/numerics/c.math/cmath.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/cmath.pass.cpp
@@ -8,7 +8,7 @@
 
 // This test fails because Clang no longer enables -fdelayed-template-parsing
 // by default on Windows with C++20 (#69431).
-// XFAIL: msvc && (clang-18 || clang-19 || clang-20 || clang-21)
+// XFAIL: msvc && (clang-19 || clang-20 || clang-21)
 
 // <cmath>
 
diff --git a/libcxx/test/std/numerics/c.math/signbit.pass.cpp b/libcxx/test/std/numerics/c.math/signbit.pass.cpp
index 46cdfd7cab1f4..94dcfccbe898c 100644
--- a/libcxx/test/std/numerics/c.math/signbit.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/signbit.pass.cpp
@@ -12,7 +12,7 @@
 // UNSUPPORTED: windows
 
 // These compilers don't support constexpr `__builtin_signbit` yet.
-// UNSUPPORTED: clang-18, clang-19, apple-clang-15, apple-clang-16, apple-clang-17
+// UNSUPPORTED: clang-19, apple-clang-17
 
 // GCC warns about signbit comparing `bool_v < 0`, which we're testing
 // ADDITIONAL_COMPILE_FLAGS(gcc): -Wno-bool-compare
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/add_sat.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/add_sat.pass.cpp
index 43481323e800c..f49e19acf0234 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/add_sat.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/add_sat.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++26
 
-// The test uses "Placeholder variables with no name"
-// UNSUPPORTED: apple-clang-15, apple-clang-16
-
 // <numeric>
 
 // template<class T>
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/div_sat.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/div_sat.pass.cpp
index ef312b7e3a911..0789213163847 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/div_sat.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/div_sat.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++26
 
-// The test uses "Placeholder variables with no name"
-// UNSUPPORTED: apple-clang-15, apple-clang-16
-
 // <numeric>
 
 // template<class T>
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/mul_sat.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/mul_sat.pass.cpp
index 94bc7ad7c48d4..f09bf30771102 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/mul_sat.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/mul_sat.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++26
 
-// The test uses "Placeholder variables with no name"
-// UNSUPPORTED: apple-clang-15, apple-clang-16
-
 // <numeric>
 
 // template<class T>
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/saturate_cast.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/saturate_cast.pass.cpp
index 79d6e2643fc4e..86e2e61647be8 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/saturate_cast.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/saturate_cast.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++26
 
-// The test uses "Placeholder variables with no name"
-// UNSUPPORTED: apple-clang-15, apple-clang-16
-
 // <numeric>
 
 // template<class R, class T>
diff --git a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/sub_sat.pass.cpp b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/sub_sat.pass.cpp
index 92ddc30aefc66..c2be8c5a47bdf 100644
--- a/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/sub_sat.pass.cpp
+++ b/libcxx/test/std/numerics/numeric.ops/numeric.ops.sat/sub_sat.pass.cpp
@@ -8,9 +8,6 @@
 
 // REQUIRES: std-at-least-c++26
 
-// The test uses "Placeholder variables with no name"
-// UNSUPPORTED: apple-clang-15, apple-clang-16
-
 // <numeric>
 
 // template<class T>
diff --git a/libcxx/test/std/ranges/range.utility/range.utility.conv/to_deduction.pass.cpp b/libcxx/test/std/ranges/range.utility/range.utility.conv/to_deduction.pass.cpp
index 58307bd88d0fe..29572ab3c4b13 100644
--- a/libcxx/test/std/ranges/range.utility/range.utility.conv/to_deduction.pass.cpp
+++ b/libcxx/test/std/ranges/range.utility/range.utility.conv/to_deduction.pass.cpp
@@ -7,9 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
-// There is a bug in older versions of Clang that causes trouble with constraints in classes like
-// `ContainerWithDirectCtr`.
-// XFAIL: apple-clang-15
 
 // template<template<class...> class C, input_range R, class... Args>
 //   constexpr auto to(R&& r, Args&&... args);  // Since C++23
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp
index 20e0a5ed66bd0..68fe8b6de41d6 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.pass.cpp
@@ -8,8 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
 // UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
-// The tested functionality needs deducing this.
-// XFAIL: apple-clang
 
 // <format>
 
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
index 8a79dd4d50f20..4ae63e896caed 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit.return_type.pass.cpp
@@ -8,8 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
 // UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
-// The tested functionality needs deducing this.
-// XFAIL: apple-clang
 
 // <format>
 
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp
index 146ceba58872e..77df72d3c4c6c 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.deprecated.verify.cpp
@@ -8,7 +8,6 @@
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
 // UNSUPPORTED: GCC-ALWAYS_INLINE-FIXME
-// XFAIL: apple-clang
 
 // <format>
 
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
index d99675a71f321..9138bf458342b 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.arg/visit_format_arg.pass.cpp
@@ -25,7 +25,7 @@
 #include "make_string.h"
 #include "min_allocator.h"
 
-#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+#if TEST_STD_VER >= 26
 TEST_CLANG_DIAGNOSTIC_IGNORED("-Wdeprecated-declarations")
 #endif
 
diff --git a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
index c7dd82d726b3a..cbddc4f437a53 100644
--- a/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
+++ b/libcxx/test/std/utilities/format/format.arguments/format.args/get.pass.cpp
@@ -32,7 +32,7 @@ void test(From value) {
     else
       assert(false);
   };
-#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+#if TEST_STD_VER >= 26
   format_args.get(0).visit(visitor);
 #else
   std::visit_format_arg(visitor, format_args.get(0));
@@ -47,7 +47,7 @@ void test_handle(T value) {
   std::basic_format_args<Context> format_args{store};
 
   auto visitor = [](auto a) { assert((std::is_same_v<decltype(a), typename std::basic_format_arg<Context>::handle>)); };
-#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+#if TEST_STD_VER >= 26
   format_args.get(0).visit(visitor);
 #else
   std::visit_format_arg(visitor, format_args.get(0));
@@ -73,7 +73,7 @@ void test_string_view(From value) {
     else
       assert(false);
   };
-#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+#if TEST_STD_VER >= 26
   format_args.get(0).visit(visitor);
 #else
   std::visit_format_arg(visitor, format_args.get(0));
diff --git a/libcxx/test/std/utilities/meta/meta.rel/is_virtual_base_of.pass.cpp b/libcxx/test/std/utilities/meta/meta.rel/is_virtual_base_of.pass.cpp
index f443d2030961d..f3e315a37351f 100644
--- a/libcxx/test/std/utilities/meta/meta.rel/is_virtual_base_of.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.rel/is_virtual_base_of.pass.cpp
@@ -9,7 +9,7 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
 
 // These compilers don't support __builtin_is_virtual_base_of yet.
-// UNSUPPORTED: clang-18, clang-19, gcc-14, apple-clang-16, apple-clang-17
+// UNSUPPORTED: clang-19, gcc-14, apple-clang-17
 
 // <type_traits>
 
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp
index 681ad13a07dfd..8f2f3b74ae09d 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.pass.cpp
@@ -9,7 +9,7 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // These compilers don't support __builtin_is_implicit_lifetime yet.
-// UNSUPPORTED: clang-18, clang-19, gcc-14, apple-clang-15, apple-clang-16, apple-clang-17
+// UNSUPPORTED: clang-19, gcc-14, apple-clang-17
 
 // <type_traits>
 
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.verify.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.verify.cpp
index 34462f9bf0ec6..c59f60d042eff 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.verify.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/is_implicit_lifetime.verify.cpp
@@ -9,7 +9,7 @@
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
 
 // These compilers don't support __builtin_is_implicit_lifetime yet.
-// UNSUPPORTED: clang-18, clang-19, gcc-14, apple-clang-15, apple-clang-16, apple-clang-17
+// UNSUPPORTED: clang-19, gcc-14, apple-clang-17
 
 // <type_traits>
 
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
index 5b3753c67381f..296a9575195b8 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_constructs_from_temporary.pass.cpp
@@ -9,7 +9,7 @@
 // REQUIRES: std-at-least-c++23
 
 // These compilers don't support std::reference_converts_from_temporary yet.
-// UNSUPPORTED: android, apple-clang-15, apple-clang-16, clang-19.1
+// UNSUPPORTED: android, clang-19.1
 
 // <type_traits>
 
diff --git a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
index 849e286c8cdab..f2d82206153de 100644
--- a/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
+++ b/libcxx/test/std/utilities/meta/meta.unary/meta.unary.prop/reference_converts_from_temporary.pass.cpp
@@ -9,7 +9,7 @@
 // REQUIRES: std-at-least-c++23
 
 // These compilers don't support std::reference_converts_from_temporary yet.
-// UNSUPPORTED: android, apple-clang-15, apple-clang-16, clang-18, clang-19.1
+// UNSUPPORTED: android, clang-19.1
 
 // <type_traits>
 
diff --git a/libcxx/test/std/utilities/variant/variant.visit.member/robust_against_adl.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit.member/robust_against_adl.pass.cpp
index 7be7c7ff9122b..38cf34a9c699c 100644
--- a/libcxx/test/std/utilities/variant/variant.visit.member/robust_against_adl.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit.member/robust_against_adl.pass.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
-// XFAIL: apple-clang
 
 // <variant>
 
diff --git a/libcxx/test/std/utilities/variant/variant.visit.member/visit.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit.member/visit.pass.cpp
index f68112d30fc35..aeb1297c136ae 100644
--- a/libcxx/test/std/utilities/variant/variant.visit.member/visit.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit.member/visit.pass.cpp
@@ -7,8 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
-// The tested functionality needs deducing this.
-// XFAIL: apple-clang
 
 // <variant>
 
diff --git a/libcxx/test/std/utilities/variant/variant.visit.member/visit_return_type.pass.cpp b/libcxx/test/std/utilities/variant/variant.visit.member/visit_return_type.pass.cpp
index 8093af0aba587..3fba52cf05da1 100644
--- a/libcxx/test/std/utilities/variant/variant.visit.member/visit_return_type.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.visit.member/visit_return_type.pass.cpp
@@ -7,8 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
-// The tested functionality needs deducing this.
-// XFAIL: apple-clang
 
 // <variant>
 
diff --git a/libcxx/test/support/test_basic_format_arg.h b/libcxx/test/support/test_basic_format_arg.h
index f51f6e97cbed0..99cd558c3c5bf 100644
--- a/libcxx/test/support/test_basic_format_arg.h
+++ b/libcxx/test/support/test_basic_format_arg.h
@@ -21,7 +21,7 @@ bool test_basic_format_arg(std::basic_format_arg<Context> arg, T expected) {
     else
       return false;
   };
-#if TEST_STD_VER >= 26 && defined(TEST_HAS_EXPLICIT_THIS_PARAMETER)
+#if TEST_STD_VER >= 26
   return arg.visit(std::move(visitor));
 #else
   return std::visit_format_arg(std::move(visitor), arg);
diff --git a/libcxx/test/support/test_macros.h b/libcxx/test/support/test_macros.h
index 93dbbaeeeda96..25d2e36852c48 100644
--- a/libcxx/test/support/test_macros.h
+++ b/libcxx/test/support/test_macros.h
@@ -525,13 +525,6 @@ inline Tp const& DoNotOptimize(Tp const& value) {
 #  define TEST_IF_AIX(arg_true, arg_false) arg_false
 #endif
 
-// Clang-18 has support for deducing this, but it does not set the FTM.
-#ifdef _LIBCPP_USE_FROZEN_CXX03_HEADERS
-// This is a C++20 featue, so we don't care whether the compiler could support it
-#elif defined(_LIBCPP_VERSION) && _LIBCPP_HAS_EXPLICIT_THIS_PARAMETER
-#  define TEST_HAS_EXPLICIT_THIS_PARAMETER
-#endif
-
 // Placement `operator new`/`operator new[]` are not yet constexpr in C++26
 // when using MS ABI, because they are from <vcruntime_new.h>.
 #if defined(__cpp_lib_constexpr_new) && __cpp_lib_constexpr_new >= 202406L