diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15a96fa..908adf6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,14 @@ major version, and each entry says so when it happens.
 
 ## [Unreleased]
 
+### Fixed
+
+- The upload service refused every upload with "GitHub could not save the file
+  just now". Since 2026 GitHub issues App installation tokens in a longer,
+  stateless form (`ghs_<app id>_<JWT>`, about 520 characters, with `.` and `-`),
+  and the service only accepted the old 40-character form. It now accepts both,
+  using GitHub's published pattern. Submitters' sign-in tokens are unaffected.
+
 ## [1.11.0-rc.12] — 2026-10-16
 
 Twelfth candidate. rc.11 failed closed in a deployment's update (nothing was
diff --git a/services/uploads/lib/github.mjs b/services/uploads/lib/github.mjs
index 0ca01a9..a4ea207 100644
--- a/services/uploads/lib/github.mjs
+++ b/services/uploads/lib/github.mjs
@@ -30,9 +30,16 @@ export const TOKEN_REFRESH_MARGIN_MS = 5 * 60 * 1000;
 const DEFAULT_RETRY_AFTER = 60;
 const MAX_RETRY_AFTER = 3600;
 
-/** GitHub user and installation tokens: an opaque `gh?_…`/`github_pat_…` string. */
+/** GitHub user tokens: an opaque `gh?_…`/`github_pat_…` string. */
 export const TOKEN_PATTERN = /^[A-Za-z0-9_]{20,512}$/;
 
+/**
+ * GitHub App installation tokens: the opaque `ghs_` + 36 characters, or since
+ * 2026 a stateless `ghs_<app id>_<JWT>` of about 520 characters with `.` and
+ * `-` in it. GitHub's own pattern; it gives no upper length.
+ */
+export const INSTALLATION_TOKEN_PATTERN = /^ghs_[A-Za-z0-9._-]{36,}$/;
+
 /**
  * A GitHub call that did not succeed.
  * - `unauthorized`: 401, the token is not (or no longer) valid
@@ -213,7 +220,11 @@ export async function installationToken(deps, config) {
     body: { repositories: [config.repo], permissions: { contents: 'write' } },
   });
   const expiresAt = Date.parse(minted?.expires_at ?? '');
-  if (typeof minted?.token !== 'string' || !TOKEN_PATTERN.test(minted.token) || !Number.isFinite(expiresAt)) {
+  if (
+    typeof minted?.token !== 'string' ||
+    !INSTALLATION_TOKEN_PATTERN.test(minted.token) ||
+    !Number.isFinite(expiresAt)
+  ) {
     throw new GitHubError('failed', 201, { message: 'token endpoint answered without a usable token' });
   }
   cachedToken = { key, token: minted.token, expiresAt };
diff --git a/services/uploads/test/github.test.mjs b/services/uploads/test/github.test.mjs
index 9d3546c..c4535dc 100644
--- a/services/uploads/test/github.test.mjs
+++ b/services/uploads/test/github.test.mjs
@@ -98,6 +98,35 @@ test('the installation token is reused until five minutes before it expires, the
   assert.equal(github.calls.length, 8);
 });
 
+test('installationToken takes both forms of installation token GitHub issues', async () => {
+  for (const token of ['ghs_' + 'I'.repeat(36), INSTALL_TOKEN]) {
+    clearInstallationTokenCache();
+    const github = fakeGitHub({
+      routes: {
+        [`POST /app/installations/${INSTALLATION_ID}/access_tokens`]: () =>
+          json(201, { token, expires_at: new Date(NOW + 60 * 60 * 1000).toISOString() }),
+      },
+    });
+    assert.equal(await installationToken({ fetch: github, now: () => NOW }, CONFIG), token);
+  }
+  assert.ok(INSTALL_TOKEN.length > 500 && /[.-]/.test(INSTALL_TOKEN), 'the fixture is the long form');
+  for (const token of [
+    'ghs_' + 'I'.repeat(35),
+    `${INSTALL_TOKEN} x`,
+    `${INSTALL_TOKEN}\nx`,
+    'ghu_' + 'I'.repeat(36),
+  ]) {
+    clearInstallationTokenCache();
+    const github = fakeGitHub({
+      routes: {
+        [`POST /app/installations/${INSTALLATION_ID}/access_tokens`]: () =>
+          json(201, { token, expires_at: new Date(NOW + 60 * 60 * 1000).toISOString() }),
+      },
+    });
+    await assert.rejects(installationToken({ fetch: github, now: () => NOW }, CONFIG), GitHubError);
+  }
+});
+
 test('installationToken refuses an answer without a usable token', async () => {
   const github = fakeGitHub({
     routes: { [`POST /app/installations/${INSTALLATION_ID}/access_tokens`]: () => json(201, { token: 'x' }) },
diff --git a/services/uploads/test/helpers.mjs b/services/uploads/test/helpers.mjs
index 959b37b..42a976a 100644
--- a/services/uploads/test/helpers.mjs
+++ b/services/uploads/test/helpers.mjs
@@ -10,7 +10,8 @@ export const SITE = 'https://acme.github.io';
 export const OWNER = 'acme';
 export const REPO = 'catalog-uploads';
 export const USER_TOKEN = 'ghu_' + 'U'.repeat(36);
-export const INSTALL_TOKEN = 'ghs_' + 'I'.repeat(36);
+/** The stateless form GitHub has issued since 2026: `ghs_<app id>_<JWT>`, about 520 characters. */
+export const INSTALL_TOKEN = `ghs_123456_${'eyJ' + 'I'.repeat(60)}.${'eyJ' + 'P-_'.repeat(100)}.${'S'.repeat(140)}`;
 export const USER_ID = 4242;
 export const INSTALLATION_ID = 77;
 export const SET = 'abcdefghijklmnopqrstuvwx23';