diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -86,6 +86,8 @@
 // ... add new file formats here ...
 #  endif
 
+// ABI {
+
 #  if _LIBCPP_ABI_VERSION >= 2
 // Change short string representation so that string data starts at offset 0,
 // improving its alignment in some cases.
@@ -191,6 +193,23 @@
 #    define _LIBCPP_ABI_BAD_FUNCTION_CALL_KEY_FUNCTION
 #  endif
 
+// Changes the iterator type of select containers (see below) to a bounded iterator that:
+// - keeps track of which container it refers to;
+// - keeps track of whether it's valid or not and asserts validity on every dereference;
+// - allows enabling the check that a given range is valid (sentinel is reachable from the begin iterator, etc.) in
+//   constant time.
+//
+// ABI impact: increases the size and changes the layout of containers (to store additional information that is used by
+// bounded iterators), changes the return type of container functions that return iterators.
+//
+// Supported containers:
+// - `span`;
+// - `string_view`;
+// - `array`.
+// #define _LIBCPP_ABI_BOUNDED_ITERATORS
+
+// } ABI
+
 #  define _LIBCPP_TOSTRING2(x) #x
 #  define _LIBCPP_TOSTRING(x) _LIBCPP_TOSTRING2(x)
 
diff --git a/libcxx/include/__config_site.in b/libcxx/include/__config_site.in
--- a/libcxx/include/__config_site.in
+++ b/libcxx/include/__config_site.in
@@ -30,6 +30,7 @@
 #cmakedefine _LIBCPP_HAS_NO_WIDE_CHARACTERS
 #cmakedefine01 _LIBCPP_ENABLE_ASSERTIONS_DEFAULT
 #cmakedefine _LIBCPP_ENABLE_DEBUG_MODE
+#cmakedefine _LIBCPP_ABI_BOUNDED_ITERATORS
 
 // PSTL backends
 #cmakedefine _LIBCPP_PSTL_CPU_BACKEND_SERIAL
diff --git a/libcxx/include/__debug b/libcxx/include/__debug
--- a/libcxx/include/__debug
+++ b/libcxx/include/__debug
@@ -27,8 +27,8 @@
 # define _LIBCPP_DEBUG_STRICT_WEAK_ORDERING_CHECK
 #endif
 
-#if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING)
-# define _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#if defined(_LIBCPP_ENABLE_DEBUG_MODE) && !defined(_LIBCPP_ABI_BOUNDED_ITERATORS)
+# define _LIBCPP_ABI_BOUNDED_ITERATORS
 #endif
 
 #ifdef _LIBCPP_ENABLE_DEBUG_MODE
diff --git a/libcxx/include/span b/libcxx/include/span
--- a/libcxx/include/span
+++ b/libcxx/include/span
@@ -214,7 +214,7 @@
     using const_pointer          = const _Tp *;
     using reference              = _Tp &;
     using const_reference        = const _Tp &;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using iterator               = __bounded_iter<pointer>;
 #else
     using iterator               = __wrap_iter<pointer>;
@@ -359,14 +359,14 @@
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator begin() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return iterator(this, data());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator end() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return iterator(this, data() + size());
@@ -398,7 +398,7 @@
     using const_pointer          = const _Tp *;
     using reference              = _Tp &;
     using const_reference        = const _Tp &;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using iterator               = __bounded_iter<pointer>;
 #else
     using iterator               = __wrap_iter<pointer>;
@@ -525,14 +525,14 @@
 
 // [span.iter], span iterator support
     _LIBCPP_INLINE_VISIBILITY constexpr iterator begin() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return iterator(this, data());
 #endif
     }
     _LIBCPP_INLINE_VISIBILITY constexpr iterator end() const noexcept {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return iterator(this, data() + size());
diff --git a/libcxx/include/string_view b/libcxx/include/string_view
--- a/libcxx/include/string_view
+++ b/libcxx/include/string_view
@@ -274,7 +274,7 @@
     using const_pointer          = const _CharT*;
     using reference              = _CharT&;
     using const_reference        = const _CharT&;
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
     using const_iterator         = __bounded_iter<const_pointer>;
 #else
     using const_iterator         = const_pointer; // See [string.view.iterators]
@@ -355,7 +355,7 @@
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator cbegin() const _NOEXCEPT {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data(), data(), data() + size());
 #else
         return __data_;
@@ -364,7 +364,7 @@
 
     _LIBCPP_CONSTEXPR _LIBCPP_INLINE_VISIBILITY
     const_iterator cend()   const _NOEXCEPT {
-#ifdef _LIBCPP_DEBUG_ITERATOR_BOUNDS_CHECKING
+#ifdef _LIBCPP_ABI_BOUNDED_ITERATORS
         return std::__make_bounded_iter(data() + size(), data(), data() + size());
 #else
         return __data_ + __size_;