diff --git a/.version b/.version
index 62c36bbb17f..b9b543d4254 100644
--- a/.version
+++ b/.version
@@ -1 +1 @@
-21.03
+21.05
diff --git a/nixos/doc/manual/release-notes/release-notes.xml b/nixos/doc/manual/release-notes/release-notes.xml
index bf18457c2b3..e083d51406c 100644
--- a/nixos/doc/manual/release-notes/release-notes.xml
+++ b/nixos/doc/manual/release-notes/release-notes.xml
@@ -8,7 +8,7 @@
   This section lists the release notes for each stable version of NixOS and
   current unstable revision.
  </para>
- <xi:include href="rl-2103.xml" />
+ <xi:include href="rl-2105.xml" />
  <xi:include href="rl-2009.xml" />
  <xi:include href="rl-2003.xml" />
  <xi:include href="rl-1909.xml" />
diff --git a/nixos/doc/manual/release-notes/rl-2009.xml b/nixos/doc/manual/release-notes/rl-2009.xml
index 0b1d0d509d7..a6cff1a8fae 100644
--- a/nixos/doc/manual/release-notes/rl-2009.xml
+++ b/nixos/doc/manual/release-notes/rl-2009.xml
@@ -6,7 +6,9 @@
  <title>Release 20.09 (“Nightingale”, 2020.10/27)</title>
 
   <para>
-   Support is planned until the end of April 2021, handing over to 21.03.
+   Support is planned until the end of June 2021, handing over to 21.05.
+   (Plans <link xlink:href="https://github.com/NixOS/rfcs/blob/master/rfcs/0080-nixos-release-schedule.md#core-changes">
+   have shifted</link> by two months since release of 20.09.)
   </para>
  <section xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
@@ -1538,7 +1540,7 @@ services.transmission.settings.rpc-bind-address = "0.0.0.0";
    <listitem>
     <para>
      Specifying <link linkend="opt-services.dovecot2.mailboxes">mailboxes</link> in the <package>dovecot2</package> module
-     as a list is deprecated and will break eval in 21.03. Instead, an attribute-set should be specified where the <literal>name</literal>
+     as a list is deprecated and will break eval in 21.05. Instead, an attribute-set should be specified where the <literal>name</literal>
      should be the key of the attribute.
     </para>
     <para>
diff --git a/nixos/doc/manual/release-notes/rl-2103.xml b/nixos/doc/manual/release-notes/rl-2105.xml
similarity index 98%
rename from nixos/doc/manual/release-notes/rl-2103.xml
rename to nixos/doc/manual/release-notes/rl-2105.xml
index b76d0930290..6dd14d6051e 100644
--- a/nixos/doc/manual/release-notes/rl-2103.xml
+++ b/nixos/doc/manual/release-notes/rl-2105.xml
@@ -2,14 +2,14 @@
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
-         xml:id="sec-release-21.03">
- <title>Release 21.03 (“Okapi”, 2021.03/??)</title>
+         xml:id="sec-release-21.05">
+ <title>Release 21.05 (“Okapi”, 2021.05/??)</title>
 
  <section xmlns="http://docbook.org/ns/docbook"
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
-         xml:id="sec-release-21.03-highlights">
+         xml:id="sec-release-21.05-highlights">
   <title>Highlights</title>
 
   <para>
@@ -20,7 +20,7 @@
   <itemizedlist>
    <listitem>
     <para>
-     Support is planned until the end of October 2021, handing over to 21.09.
+     Support is planned until the end of December 2021, handing over to 21.11.
     </para>
    </listitem>
    <listitem>
@@ -46,7 +46,7 @@
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
-         xml:id="sec-release-21.03-new-services">
+         xml:id="sec-release-21.05-new-services">
   <title>New Services</title>
 
   <para>
@@ -82,7 +82,7 @@
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
-         xml:id="sec-release-21.03-incompatibilities">
+         xml:id="sec-release-21.05-incompatibilities">
   <title>Backward Incompatibilities</title>
 
   <para>
@@ -501,7 +501,7 @@ self: super:
          xmlns:xlink="http://www.w3.org/1999/xlink"
          xmlns:xi="http://www.w3.org/2001/XInclude"
          version="5.0"
-         xml:id="sec-release-21.03-notable-changes">
+         xml:id="sec-release-21.05-notable-changes">
   <title>Other Notable Changes</title>
 
   <itemizedlist>
diff --git a/nixos/modules/services/mail/dovecot.nix b/nixos/modules/services/mail/dovecot.nix
index 03e7e40e388..a2298152b02 100644
--- a/nixos/modules/services/mail/dovecot.nix
+++ b/nixos/modules/services/mail/dovecot.nix
@@ -463,7 +463,7 @@ in
     environment.systemPackages = [ dovecotPkg ];
 
     warnings = mkIf (any isList options.services.dovecot2.mailboxes.definitions) [
-      "Declaring `services.dovecot2.mailboxes' as a list is deprecated and will break eval in 21.03! See the release notes for more info for migration."
+      "Declaring `services.dovecot2.mailboxes' as a list is deprecated and will break eval in 21.05! See the release notes for more info for migration."
     ];
 
     assertions = [
diff --git a/nixos/modules/services/networking/kresd.nix b/nixos/modules/services/networking/kresd.nix
index 074830fc352..4131ff8be5d 100644
--- a/nixos/modules/services/networking/kresd.nix
+++ b/nixos/modules/services/networking/kresd.nix
@@ -140,7 +140,7 @@ in {
 
     # Try cleaning up the previously default location of cache file.
     # Note that /var/cache/* should always be safe to remove.
-    # TODO: remove later, probably between 20.09 and 21.03
+    # TODO: remove later, probably between 20.09 and 21.05
     systemd.tmpfiles.rules = [ "R /var/cache/kresd" ];
   };
 }
diff --git a/nixos/modules/services/web-apps/hedgedoc.nix b/nixos/modules/services/web-apps/hedgedoc.nix
index 3f646d7db0c..d940f3d3dae 100644
--- a/nixos/modules/services/web-apps/hedgedoc.nix
+++ b/nixos/modules/services/web-apps/hedgedoc.nix
@@ -5,6 +5,10 @@ with lib;
 let
   cfg = config.services.hedgedoc;
 
+  # 21.03 will not be an official release - it was instead 21.05.  This
+  # versionAtLeast statement remains set to 21.03 for backwards compatibility.
+  # See https://github.com/NixOS/nixpkgs/pull/108899 and
+  # https://github.com/NixOS/rfcs/blob/master/rfcs/0080-nixos-release-schedule.md.
   name = if versionAtLeast config.system.stateVersion "21.03"
     then "hedgedoc"
     else "codimd";
diff --git a/nixos/modules/services/web-apps/nextcloud.nix b/nixos/modules/services/web-apps/nextcloud.nix
index c5c14050b5c..60d40355335 100644
--- a/nixos/modules/services/web-apps/nextcloud.nix
+++ b/nixos/modules/services/web-apps/nextcloud.nix
@@ -368,7 +368,7 @@ in {
         '')
         ++ (optional (versionOlder cfg.package.version "18") (upgradeWarning 17 "20.03"))
         ++ (optional (versionOlder cfg.package.version "19") (upgradeWarning 18 "20.09"))
-        ++ (optional (versionOlder cfg.package.version "20") (upgradeWarning 19 "21.03"));
+        ++ (optional (versionOlder cfg.package.version "20") (upgradeWarning 19 "21.05"));
 
       services.nextcloud.package = with pkgs;
         mkDefault (
@@ -380,6 +380,10 @@ in {
             ''
           else if versionOlder stateVersion "20.03" then nextcloud17
           else if versionOlder stateVersion "20.09" then nextcloud18
+          # 21.03 will not be an official release - it was instead 21.05.
+          # This versionOlder statement remains set to 21.03 for backwards compatibility.
+          # See https://github.com/NixOS/nixpkgs/pull/108899 and
+          # https://github.com/NixOS/rfcs/blob/master/rfcs/0080-nixos-release-schedule.md.
           else if versionOlder stateVersion "21.03" then nextcloud19
           else nextcloud20
         );
diff --git a/pkgs/applications/editors/emacs-modes/melpa-packages.nix b/pkgs/applications/editors/emacs-modes/melpa-packages.nix
index 9334a16d22d..62979b4226d 100644
--- a/pkgs/applications/editors/emacs-modes/melpa-packages.nix
+++ b/pkgs/applications/editors/emacs-modes/melpa-packages.nix
@@ -610,7 +610,7 @@ let
       };
 
       # Deprecated legacy aliases for backwards compat
-      aliases = lib.listToAttrs (lib.attrValues (lib.mapAttrs (n: v: { name = v; value = builtins.trace "Melpa attribute '${v}' is a legacy alias that will be removed in 21.03, use '${n}' instead" melpaPackages.${n}; }) (lib.filterAttrs (n: v: lib.hasAttr n melpaPackages) {
+      aliases = lib.listToAttrs (lib.attrValues (lib.mapAttrs (n: v: { name = v; value = builtins.trace "Melpa attribute '${v}' is a legacy alias that will be removed in 21.05, use '${n}' instead" melpaPackages.${n}; }) (lib.filterAttrs (n: v: lib.hasAttr n melpaPackages) {
         "auto-complete-clang-async" = "emacsClangCompleteAsync";
         "vterm" = "emacs-libvterm";
         "0xc" = "_0xc";
diff --git a/pkgs/top-level/aliases.nix b/pkgs/top-level/aliases.nix
index 77ca1204bf4..f4fb2110f1d 100644
--- a/pkgs/top-level/aliases.nix
+++ b/pkgs/top-level/aliases.nix
@@ -846,7 +846,7 @@ mapAliases ({
 
   todolist = throw "todolist is now ultralist."; # added 2020-12-27
 
-  /* Cleanup before 21.03 */
+  /* Cleanup before 21.05 */
   riot-desktop = throw "riot-desktop is now element-desktop!";
   riot-web = throw "riot-web is now element-web";