diff --git a/libcxx/include/__format/buffer.h b/libcxx/include/__format/buffer.h
--- a/libcxx/include/__format/buffer.h
+++ b/libcxx/include/__format/buffer.h
@@ -16,6 +16,7 @@
 #include <__algorithm/min.h>
 #include <__algorithm/transform.h>
 #include <__algorithm/unwrap_iter.h>
+#include <__availability>
 #include <__config>
 #include <__format/concepts.h>
 #include <__format/enable_insertable.h>
@@ -50,7 +51,7 @@
 /// type-erasure for the formatting functions. This reduces the number to
 /// template instantiations.
 template <__fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __output_buffer {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __output_buffer {
 public:
   using value_type = _CharT;
 
@@ -223,7 +224,7 @@
 /// This storage is used when writing a single element to the output iterator
 /// is expensive.
 template <__fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __internal_storage {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __internal_storage {
 public:
   _LIBCPP_HIDE_FROM_ABI _CharT* __begin() { return __buffer_; }
 
@@ -239,7 +240,7 @@
 /// Since the output is directly written to the underlying storage this class
 /// is just an empty class.
 template <__fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __direct_storage {};
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __direct_storage {};
 
 template <class _OutIt, class _CharT>
 concept __enable_direct_output = __fmt_char_type<_CharT> &&
@@ -251,7 +252,7 @@
 
 /// Write policy for directly writing to the underlying output.
 template <class _OutIt, __fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __writer_direct {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __writer_direct {
 public:
   _LIBCPP_HIDE_FROM_ABI explicit __writer_direct(_OutIt __out_it)
       : __out_it_(__out_it) {}
@@ -270,7 +271,7 @@
 
 /// Write policy for copying the buffer to the output.
 template <class _OutIt, __fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __writer_iterator {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __writer_iterator {
 public:
   _LIBCPP_HIDE_FROM_ABI explicit __writer_iterator(_OutIt __out_it)
       : __out_it_{_VSTD::move(__out_it)} {}
@@ -300,18 +301,18 @@
 
 /// Extract the container type of a \ref back_insert_iterator.
 template <class _It>
-struct _LIBCPP_TEMPLATE_VIS __back_insert_iterator_container {
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __back_insert_iterator_container {
   using type = void;
 };
 
 template <__insertable _Container>
-struct _LIBCPP_TEMPLATE_VIS __back_insert_iterator_container<back_insert_iterator<_Container>> {
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __back_insert_iterator_container<back_insert_iterator<_Container>> {
   using type = _Container;
 };
 
 /// Write policy for inserting the buffer in a container.
 template <class _Container>
-class _LIBCPP_TEMPLATE_VIS __writer_container {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __writer_container {
 public:
   using _CharT = typename _Container::value_type;
 
@@ -330,7 +331,7 @@
 
 /// Selects the type of the writer used for the output iterator.
 template <class _OutIt, class _CharT>
-class _LIBCPP_TEMPLATE_VIS __writer_selector {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __writer_selector {
   using _Container = typename __back_insert_iterator_container<_OutIt>::type;
 
 public:
@@ -341,7 +342,7 @@
 
 /// The generic formatting buffer.
 template <class _OutIt, __fmt_char_type _CharT>
-requires(output_iterator<_OutIt, const _CharT&>) class _LIBCPP_TEMPLATE_VIS
+requires(output_iterator<_OutIt, const _CharT&>) class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT
     __format_buffer {
   using _Storage =
       conditional_t<__enable_direct_output<_OutIt, _CharT>,
@@ -377,7 +378,7 @@
 /// Since \ref formatted_size only needs to know the size, the output itself is
 /// discarded.
 template <__fmt_char_type _CharT>
-class _LIBCPP_TEMPLATE_VIS __formatted_size_buffer {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __formatted_size_buffer {
 public:
   _LIBCPP_HIDE_FROM_ABI auto __make_output_iterator() { return __output_.__make_output_iterator(); }
 
@@ -397,7 +398,7 @@
 /// The base of a buffer that counts and limits the number of insertions.
 template <class _OutIt, __fmt_char_type _CharT, bool>
   requires(output_iterator<_OutIt, const _CharT&>)
-struct _LIBCPP_TEMPLATE_VIS __format_to_n_buffer_base {
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __format_to_n_buffer_base {
   using _Size = iter_difference_t<_OutIt>;
 
 public:
@@ -427,7 +428,7 @@
 /// exceed the maximum number of code units.
 template <class _OutIt, __fmt_char_type _CharT>
   requires(output_iterator<_OutIt, const _CharT&>)
-class _LIBCPP_TEMPLATE_VIS __format_to_n_buffer_base<_OutIt, _CharT, true> {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __format_to_n_buffer_base<_OutIt, _CharT, true> {
   using _Size = iter_difference_t<_OutIt>;
 
 public:
@@ -477,7 +478,7 @@
 /// The buffer that counts and limits the number of insertions.
 template <class _OutIt, __fmt_char_type _CharT>
   requires(output_iterator<_OutIt, const _CharT&>)
-struct _LIBCPP_TEMPLATE_VIS __format_to_n_buffer final
+struct _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __format_to_n_buffer final
     : public __format_to_n_buffer_base< _OutIt, _CharT, __enable_direct_output<_OutIt, _CharT>> {
   using _Base = __format_to_n_buffer_base<_OutIt, _CharT, __enable_direct_output<_OutIt, _CharT>>;
   using _Size = iter_difference_t<_OutIt>;
@@ -492,6 +493,7 @@
     return {_VSTD::move(this->__writer_).__out_it(), this->__size_};
   }
 };
+
 } // namespace __format
 
 #endif //_LIBCPP_STD_VER > 17
diff --git a/libcxx/include/__format/format_arg.h b/libcxx/include/__format/format_arg.h
--- a/libcxx/include/__format/format_arg.h
+++ b/libcxx/include/__format/format_arg.h
@@ -140,7 +140,7 @@
 /// This is a separate type so it's possible to store the values and types in
 /// separate arrays.
 template <class _Context>
-class __basic_format_arg_value {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __basic_format_arg_value {
   using _CharT = typename _Context::char_type;
 
 public:
@@ -251,7 +251,7 @@
 };
 
 template <class _Context>
-class _LIBCPP_TEMPLATE_VIS basic_format_arg<_Context>::handle {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT basic_format_arg<_Context>::handle {
 public:
   _LIBCPP_HIDE_FROM_ABI
   void format(basic_format_parse_context<char_type>& __parse_ctx, _Context& __ctx) const {
diff --git a/libcxx/include/__format/formatter_floating_point.h b/libcxx/include/__format/formatter_floating_point.h
--- a/libcxx/include/__format/formatter_floating_point.h
+++ b/libcxx/include/__format/formatter_floating_point.h
@@ -16,6 +16,7 @@
 #include <__algorithm/min.h>
 #include <__algorithm/rotate.h>
 #include <__algorithm/transform.h>
+#include <__availability>
 #include <__concepts/arithmetic.h>
 #include <__concepts/same_as.h>
 #include <__config>
@@ -132,7 +133,7 @@
 /// Depending on the maxium size required for a value, the buffer is allocated
 /// on the stack or the heap.
 template <floating_point _Fp>
-class _LIBCPP_TEMPLATE_VIS __float_buffer {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __float_buffer {
   using _Traits = __traits<_Fp>;
 
 public:
diff --git a/libcxx/include/__format/parser_std_format_spec.h b/libcxx/include/__format/parser_std_format_spec.h
--- a/libcxx/include/__format/parser_std_format_spec.h
+++ b/libcxx/include/__format/parser_std_format_spec.h
@@ -241,7 +241,7 @@
 /// set to zero. That way they can be repurposed if a future revision of the
 /// Standards adds new fields to std-format-spec.
 template <class _CharT>
-class _LIBCPP_TEMPLATE_VIS __parser {
+class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT __parser {
 public:
   _LIBCPP_HIDE_FROM_ABI constexpr auto __parse(basic_format_parse_context<_CharT>& __parse_ctx, __fields __fields)
       -> decltype(__parse_ctx.begin()) {
diff --git a/libcxx/test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp b/libcxx/test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp
--- a/libcxx/test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp
+++ b/libcxx/test/std/utilities/variant/variant.variant/variant.ctor/copy.pass.cpp
@@ -253,15 +253,11 @@
   test_copy_ctor_valueless_by_exception();
   test_copy_ctor_sfinae();
   test_constexpr_copy_ctor();
-#if 0
-// disable this for the moment; it fails on older compilers.
-//  Need to figure out which compilers will support it.
-{ // This is the motivating example from P0739R0
-  std::variant<int, double> v1(3);
-  std::variant v2 = v1;
-  (void) v2;
-}
-#endif
+  { // This is the motivating example from P0739R0
+    std::variant<int, double> v1(3);
+    std::variant v2 = v1;
+    (void)v2;
+  }
 
   return 0;
 }