document that `sys._is_gil_enabled` is CPython-specific (#131748)

diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
index 2bdfb337f02056b25bb0c91ea2ff8491f84d2af0..bb88cf73ec1e8917ac9c0eeb527038067be8c199 100644 (file)
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -1247,6 +1247,9 @@ always available. Unless explicitly noted otherwise, all variables are read-only
 
    .. versionadded:: 3.13
 
+   .. impl-detail::
+
+      It is not guaranteed to exist in all implementations of Python.
 
 .. function:: is_finalizing()