diff --git a/doc/redirects.json b/doc/redirects.json
index f5dbb8bb65f8..03285903666e 100644
--- a/doc/redirects.json
+++ b/doc/redirects.json
@@ -869,6 +869,9 @@
   "tar-files": [
     "index.html#tar-files"
   ],
+  "x86_64-darwin-26.05": [
+    "release-notes.html#x86_64-darwin-26.05"
+  ],
   "zip-files": [
     "index.html#zip-files"
   ],
diff --git a/doc/release-notes/rl-2605.section.md b/doc/release-notes/rl-2605.section.md
index cf9f53baba96..0d70f1108d58 100644
--- a/doc/release-notes/rl-2605.section.md
+++ b/doc/release-notes/rl-2605.section.md
@@ -12,6 +12,27 @@
 - Ruby default version has been updated from 3.3 to 3.4.
   Refer to the [upstream release announcement](https://www.ruby-lang.org/en/news/2024/12/25/ruby-3-4-0-released/) for details.
 
+- []{#x86_64-darwin-26.05}
+
+  **This will be the last release of Nixpkgs to support `x86_64-darwin`.**
+  Platform support will be maintained and binaries built until Nixpkgs 26.05 goes out of support at the end of 2026.
+  For 26.11, due to Apple’s deprecation of the platform and limited build infrastructure and developer time, we will no longer build packages for `x86_64-darwin` or support building them from source.
+
+  By the time of 26.11’s release, Homebrew will offer only limited [Tier 3](https://docs.brew.sh/Support-Tiers#tier-3) support for the platform, but MacPorts will likely continue to support it for a long time.
+  We also recommend users consider installing NixOS, which should continue to run on essentially all Intel Macs, especially after Apple stops security support for macOS 26 in 2028.
+
+  A warning will be displayed for `x86_64-darwin` users; you can set [](#opt-allowDeprecatedx86_64Darwin) in the [Nixpkgs configuration](https://nixos.org/manual/nixpkgs/stable/#chap-packageconfig) to silence it.
+  The {file}`~/.config/nixpkgs/config.nix` file will not work for users of flakes, who can instead replace `nixpkgs.legacyPackages.x86_64-darwin` with
+
+  ```nix
+  import nixpkgs {
+    system = "x86_64-darwin";
+    config.allowDeprecatedx86_64Darwin = true;
+  }
+  ```
+
+  nix-darwin users can set [`nixpkgs.config.allowDeprecatedx86_64Darwin`](https://nix-darwin.github.io/nix-darwin/manual/index.html#opt-nixpkgs.config) in their system configurations.
+
 - The Factor programming language has been updated to Version 0.101 bringing various improvements to UI rendering and HiDPI support as well as support for Unicode 17.0.0.
   Starting from Version 0.100, the Factor VM is compiled with Clang.
 
diff --git a/pkgs/top-level/config.nix b/pkgs/top-level/config.nix
index 7efb30525420..8f700a07eb0e 100644
--- a/pkgs/top-level/config.nix
+++ b/pkgs/top-level/config.nix
@@ -451,8 +451,8 @@ let
         Silence the warning for the upcoming deprecation of the
         `x86_64-darwin` platform in Nixpkgs 26.11.
 
-        This does nothing in 25.11, and is provided there for forward
-        compatibility of configurations with 26.05.
+        See the [release notes](#x86_64-darwin-26.05) for more
+        information.
       '';
     };
 
diff --git a/pkgs/top-level/default.nix b/pkgs/top-level/default.nix
index 607145be06aa..521745d67ec9 100644
--- a/pkgs/top-level/default.nix
+++ b/pkgs/top-level/default.nix
@@ -18,6 +18,25 @@
   or dot-files.
 */
 
+let
+  # We hoist this above the closure so that the same thunk is shared
+  # between multiple imports of Nixpkgs. This ensures that commands
+  # like `nix eval nixpkgs#legacyPackages.x86_64-darwin.pkgsStatic.hello`
+  # print only one warning, which would otherwise be spammy in common
+  # scenarios that instantiate many copies of Nixpkgs.
+  #
+  # Unfortunately, flakes’ handling of transitive dependencies mean
+  # that it’s still likely users will see multiple warnings, but
+  # there’s nothing we can do about that within the constraints of the
+  # Nix language.
+  x86_64DarwinDeprecationWarning =
+    pristineLib.warn
+      "Nixpkgs 26.05 will be the last release to support x86_64-darwin; see https://nixos.org/manual/nixpkgs/unstable/release-notes#x86_64-darwin-26.05"
+      (x: x);
+
+  pristineLib = import ../../lib;
+in
+
 {
   # The system packages will be built on. See the manual for the
   # subtle division of labor between these two `*System`s and the three
@@ -55,8 +74,6 @@ let # Rename the function arguments
 
 in
 let
-  pristineLib = import ../../lib;
-
   lib =
     if __allowFileset then
       pristineLib
@@ -82,8 +99,17 @@ let
     (throwIfNot (lib.isList overlays) "The overlays argument to nixpkgs must be a list.")
       (throwIfNot (lib.all lib.isFunction overlays) "All overlays passed to nixpkgs must be functions.")
       (throwIfNot (lib.isList crossOverlays) "The crossOverlays argument to nixpkgs must be a list.")
+      (throwIfNot (lib.all lib.isFunction crossOverlays) "All crossOverlays passed to nixpkgs must be functions.")
       (
-        throwIfNot (lib.all lib.isFunction crossOverlays) "All crossOverlays passed to nixpkgs must be functions."
+        if
+          (
+            ((localSystem.isDarwin && localSystem.isx86) || (crossSystem.isDarwin && crossSystem.isx86))
+            && config.allowDeprecatedx86_64Darwin == false
+          )
+        then
+          x86_64DarwinDeprecationWarning
+        else
+          x: x
       );
 
   localSystem = lib.systems.elaborate args.localSystem;
diff --git a/pkgs/top-level/nixpkgs-basic-release-checks.nix b/pkgs/top-level/nixpkgs-basic-release-checks.nix
index ed88991dd2cd..7ec445402772 100644
--- a/pkgs/top-level/nixpkgs-basic-release-checks.nix
+++ b/pkgs/top-level/nixpkgs-basic-release-checks.nix
@@ -56,7 +56,7 @@ pkgs.runCommand "nixpkgs-release-checks"
           set -x
           nix-env -f $src \
               --show-trace --argstr system "$platform" \
-              --arg config '{ allowAliases = false; }' \
+              --arg config '{ allowAliases = false; allowDeprecatedx86_64Darwin = true; }' \
               --option experimental-features 'no-url-literals' \
               -qa --drv-path --system-filter \* --system \
               "''${opts[@]}" 2> eval-warnings.log > packages1
@@ -72,7 +72,7 @@ pkgs.runCommand "nixpkgs-release-checks"
 
         nix-env -f $src2 \
             --show-trace --argstr system "$platform" \
-            --arg config '{ allowAliases = false; }' \
+            --arg config '{ allowAliases = false; allowDeprecatedx86_64Darwin = true; }' \
             --option experimental-features 'no-url-literals' \
             -qa --drv-path --system-filter \* --system \
             "''${opts[@]}" > packages2
@@ -95,7 +95,7 @@ pkgs.runCommand "nixpkgs-release-checks"
 
         nix-env -f $src \
             --show-trace --argstr system "$platform" \
-            --arg config '{ allowAliases = false; }' \
+            --arg config '{ allowAliases = false; allowDeprecatedx86_64Darwin = true; }' \
             --option experimental-features 'no-url-literals' \
             -qa --drv-path --system-filter \* --system --meta --xml \
             "''${opts[@]}" > /dev/null