diff --git a/Lib/ipaddress.py b/Lib/ipaddress.py
index f1062a8cd052a5..7925f4034f1635 100644
--- a/Lib/ipaddress.py
+++ b/Lib/ipaddress.py
@@ -2387,6 +2387,10 @@ class _IPv6Constants:
         IPv6Network('2002::/16'),
         # RFC 9637: https://www.rfc-editor.org/rfc/rfc9637.html#section-6-2.2
         IPv6Network('3fff::/20'),
+        # RFC 9602: https://www.rfc-editor.org/rfc/rfc9602.html
+        IPv6Network('5f00::/16'),
+        # RFC 9780: https://www.rfc-editor.org/rfc/rfc9780.html
+        IPv6Network('100:0:0:1::/64'),
         IPv6Network('fc00::/7'),
         IPv6Network('fe80::/10'),
         ]
diff --git a/Lib/test/test_ipaddress.py b/Lib/test/test_ipaddress.py
index 3f017b97dc28a3..55667d57b1dcdd 100644
--- a/Lib/test/test_ipaddress.py
+++ b/Lib/test/test_ipaddress.py
@@ -2499,6 +2499,9 @@ def testReservedIpv6(self):
         self.assertFalse(ipaddress.ip_address('2002::').is_global)
         # gh-124217: conform with RFC 9637
         self.assertFalse(ipaddress.ip_address('3fff::').is_global)
+        # gh-151749: conform with RFC 9602 and RFC 9780
+        self.assertFalse(ipaddress.ip_address('5f00::').is_global)
+        self.assertFalse(ipaddress.ip_address('100:0:0:1::').is_global)
 
         # some generic IETF reserved addresses
         self.assertEqual(True, ipaddress.ip_address('100::').is_reserved)
diff --git a/Misc/NEWS.d/next/Library/2026-06-20-01-00-43.gh-issue-151749.5vLBmS.rst b/Misc/NEWS.d/next/Library/2026-06-20-01-00-43.gh-issue-151749.5vLBmS.rst
new file mode 100644
index 00000000000000..57dd6b5b2952d5
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-06-20-01-00-43.gh-issue-151749.5vLBmS.rst
@@ -0,0 +1,4 @@
+Fixed :attr:`ipaddress.IPv6Address.is_global` and
+:attr:`ipaddress.IPv6Address.is_private` for the ``5f00::/16`` (:rfc:`9602`)
+and ``100:0:0:1::/64`` (:rfc:`9780`) special-purpose ranges, which are not
+globally reachable per the IANA registry.