diff --git a/CHANGES b/CHANGES
index c05b1750ec..cbc239b142 100644
--- a/CHANGES
+++ b/CHANGES
@@ -13,6 +13,8 @@
 6299.	[port]		NetBSD has added 'hmac' to libc which collides with our
 			use of 'hmac'. [GL #4478]
 
+	--- 9.18.21 released ---
+
 6297.	[bug]		Improve LRU cleaning behaviour. [GL #4448]
 
 6296.	[func]		The "resolver-nonbackoff-tries" and
diff --git a/doc/arm/notes.rst b/doc/arm/notes.rst
index 7a51b557fa..1caec1b103 100644
--- a/doc/arm/notes.rst
+++ b/doc/arm/notes.rst
@@ -36,6 +36,7 @@ information about each release, and source code.
 .. include:: ../notes/notes-known-issues.rst
 
 .. include:: ../notes/notes-current.rst
+.. include:: ../notes/notes-9.18.21.rst
 .. include:: ../notes/notes-9.18.20.rst
 .. include:: ../notes/notes-9.18.19.rst
 .. include:: ../notes/notes-9.18.18.rst
diff --git a/doc/notes/notes-9.18.21.rst b/doc/notes/notes-9.18.21.rst
new file mode 100644
index 0000000000..12876d82f7
--- /dev/null
+++ b/doc/notes/notes-9.18.21.rst
@@ -0,0 +1,31 @@
+.. Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+..
+.. SPDX-License-Identifier: MPL-2.0
+..
+.. This Source Code Form is subject to the terms of the Mozilla Public
+.. License, v. 2.0.  If a copy of the MPL was not distributed with this
+.. file, you can obtain one at https://mozilla.org/MPL/2.0/.
+..
+.. See the COPYRIGHT file distributed with this work for additional
+.. information regarding copyright ownership.
+
+Notes for BIND 9.18.21
+----------------------
+
+Removed Features
+~~~~~~~~~~~~~~~~
+
+- Support for using AES as the DNS COOKIE algorithm (``cookie-algorithm
+  aes;``) has been deprecated and will be removed in a future release.
+  Please use the current default, SipHash-2-4, instead. :gl:`#4421`
+
+- The :any:`resolver-nonbackoff-tries` and :any:`resolver-retry-interval`
+  statements have been deprecated. Using them now causes a warning to be
+  logged. :gl:`#4405`
+
+Known Issues
+~~~~~~~~~~~~
+
+- There are no new known issues with this release. See :ref:`above
+  <relnotes_known_issues>` for a list of all known issues affecting this
+  BIND 9 branch.