diff --git a/README.md b/README.md
index 754b667..ea20417 100644
--- a/README.md
+++ b/README.md
@@ -53,7 +53,7 @@ jobs:
       contents: read
     steps:
       - uses: actions/checkout@v6.0.2
-      - uses: DeterminateSystems/determinate-nix-action@main # or v3.20.0 to pin to a release
+      - uses: DeterminateSystems/determinate-nix-action@main # or v3.21.0 to pin to a release
       - run: nix build .
 ```
 
@@ -67,10 +67,10 @@ jobs:
 Unlike `DeterminateSystems/nix-installer-action`, we fully support explicit version pinning for maximum consistency.
 This Action is **automatically tagged** for every Determinate Nix release, giving you complete control over your CI environment:
 
-📍 Pinning to `DeterminateSystems/determinate-nix-action@v3.20.0` guarantees:
+📍 Pinning to `DeterminateSystems/determinate-nix-action@v3.21.0` guarantees:
 
 - Same `nix-installer-action` revision every time
-- Consistent Determinate Nix v3.20.0 installation
+- Consistent Determinate Nix v3.21.0 installation
 - Reproducible CI workflows, even years later
 
 ✨ Using `@main` instead? You'll:
@@ -113,7 +113,7 @@ updates:
 | `source-branch`         | The branch of `nix-installer` to use (conflicts with `source-tag`, `source-revision`, `source-pr`)                                                                                                                                                                             |          |                            |
 | `source-pr`             | The PR of `nix-installer` to use (conflicts with `source-tag`, `source-revision`, `source-branch`)                                                                                                                                                                             |          |                            |
 | `source-revision`       | The revision of `nix-installer` to use (conflicts with `source-tag`, `source-branch`, `source-pr`)                                                                                                                                                                             |          |                            |
-| `source-tag`            | The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)                                                                                                                                                                             |          | `v3.20.0`                  |
+| `source-tag`            | The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)                                                                                                                                                                             |          | `v3.21.0`                  |
 | `source-url`            | A URL pointing to a `nix-installer` executable                                                                                                                                                                                                                                 |          |                            |
 | `backtrace`             | The setting for `RUST_BACKTRACE` (see https://doc.rust-lang.org/std/backtrace/index.html#environment-variables)                                                                                                                                                                |          |                            |
 | `diagnostic-endpoint`   | Diagnostic endpoint url where the installer sends data to. To disable set this to an empty string.                                                                                                                                                                             |          | `-`                        |
diff --git a/action.yml b/action.yml
index 71586f6..44aaabb 100644
--- a/action.yml
+++ b/action.yml
@@ -72,7 +72,7 @@
         "source-tag": {
             "description": "The tag of `nix-installer` to use (conflicts with `source-revision`, `source-branch`, `source-pr`)",
             "required": false,
-            "default": "v3.20.0"
+            "default": "v3.21.0"
         },
         "source-url": {
             "description": "A URL pointing to a `nix-installer` executable",
@@ -105,7 +105,7 @@
         "using": "composite",
         "steps": [
             {
-                "uses": "DeterminateSystems/nix-installer-action@4a754ab0c192f4d12cf88b5954b9dd13fd2d612e",
+                "uses": "DeterminateSystems/nix-installer-action@00199f951aeb9404028a6e4b95ad42546f73296a",
                 "with": {
                     "extra-conf": "${{ inputs.extra-conf }}",
                     "github-server-url": "${{ inputs.github-server-url }}",
diff --git a/flake.lock b/flake.lock
index bb28c19..0c559ef 100644
--- a/flake.lock
+++ b/flake.lock
@@ -2,12 +2,12 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1777954456,
-        "narHash": "sha256-hGdgeU2Nk87RAuZyYjyDjFL6LK7dAZN5RE9+hrDTkDU=",
-        "rev": "549bd84d6279f9852cae6225e372cc67fb91a4c1",
-        "revCount": 992384,
+        "lastModified": 1779357205,
+        "narHash": "sha256-cCO8aTqss5x9Ky8GWkpY0Hy5fyTZEbtifSUV8QjSzic=",
+        "rev": "f83fc3c307e74bc5fd5adb7eb6b8b13ffd2a36e1",
+        "revCount": 1002845,
         "type": "tarball",
-        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.992384%2Brev-549bd84d6279f9852cae6225e372cc67fb91a4c1/019df915-70b5-73a2-a5a4-63c620b45d9f/source.tar.gz"
+        "url": "https://api.flakehub.com/f/pinned/NixOS/nixpkgs/0.1.1002845%2Brev-f83fc3c307e74bc5fd5adb7eb6b8b13ffd2a36e1/019e50ff-852f-75f3-83b7-9b2faf16fe0c/source.tar.gz"
       },
       "original": {
         "type": "tarball",
diff --git a/tools/state.json b/tools/state.json
index 09af2d9..2a62271 100644
--- a/tools/state.json
+++ b/tools/state.json
@@ -1,5 +1,5 @@
 {
-  "nix_installer_action_revision": "4a754ab0c192f4d12cf88b5954b9dd13fd2d612e",
-  "determinate_nix_tag": "v3.20.0",
+  "nix_installer_action_revision": "00199f951aeb9404028a6e4b95ad42546f73296a",
+  "determinate_nix_tag": "v3.21.0",
   "checkout_action_tag": "v6.0.2"
 }