diff --git a/__tests__/sigstore/sigstore-cosign-old.test.itg.ts b/__tests__/sigstore/sigstore-cosign-old.test.itg.ts
new file mode 100644
index 00000000..c3efb2f8
--- /dev/null
+++ b/__tests__/sigstore/sigstore-cosign-old.test.itg.ts
@@ -0,0 +1,93 @@
+/**
+ * Copyright 2026 actions-toolkit authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import {beforeAll, describe, expect, jest, it} from '@jest/globals';
+import * as path from 'path';
+
+import {Buildx} from '../../src/buildx/buildx';
+import {Build} from '../../src/buildx/build';
+import {Install as CosignInstall} from '../../src/cosign/install';
+import {Docker} from '../../src/docker/docker';
+import {Exec} from '../../src/exec';
+import {Sigstore} from '../../src/sigstore/sigstore';
+
+const fixturesDir = path.join(__dirname, '..', '.fixtures');
+
+const runTest = process.env.GITHUB_ACTIONS && process.env.GITHUB_ACTIONS === 'true' && process.env.ImageOS && process.env.ImageOS.startsWith('ubuntu');
+
+const maybeIdToken = runTest && process.env.ACTIONS_ID_TOKEN_REQUEST_URL ? describe : describe.skip;
+
+// needs current GitHub repo info
+jest.unmock('@actions/github');
+
+beforeAll(async () => {
+  const cosignInstall = new CosignInstall();
+  const cosignBinPath = await cosignInstall.download({
+    version: 'v3.0.2'
+  });
+  await cosignInstall.install(cosignBinPath);
+}, 100000);
+
+maybeIdToken('signAttestationManifests', () => {
+  it('build, sign and verify', async () => {
+    const buildx = new Buildx();
+    const build = new Build({buildx: buildx});
+    const imageName = 'ghcr.io/docker/actions-toolkit/test';
+
+    await expect(
+      (async () => {
+        await Docker.getExecOutput(['login', '--password-stdin', '--username', process.env.GITHUB_REPOSITORY_OWNER || 'docker', 'ghcr.io'], {
+          input: Buffer.from(process.env.GITHUB_TOKEN || '')
+        });
+      })()
+    ).resolves.not.toThrow();
+
+    await expect(
+      (async () => {
+        // prettier-ignore
+        const buildCmd = await buildx.getCommand([
+          '--builder', process.env.CTN_BUILDER_NAME ?? 'default',
+          'build',
+          '-f', path.join(fixturesDir, 'hello.Dockerfile'),
+          '--provenance=mode=max',
+          '--tag', `${imageName}:sigstore-itg`,
+          '--platform', 'linux/amd64,linux/arm64',
+          '--push',
+          '--metadata-file', build.getMetadataFilePath(),
+          fixturesDir
+        ]);
+        await Exec.exec(buildCmd.command, buildCmd.args);
+      })()
+    ).resolves.not.toThrow();
+
+    const metadata = build.resolveMetadata();
+    expect(metadata).toBeDefined();
+    const buildDigest = build.resolveDigest(metadata);
+    expect(buildDigest).toBeDefined();
+
+    const sigstore = new Sigstore();
+    const signResults = await sigstore.signAttestationManifests({
+      imageNames: [imageName],
+      imageDigest: buildDigest!
+    });
+    expect(Object.keys(signResults).length).toEqual(2);
+
+    const verifyResults = await sigstore.verifySignedManifests(signResults, {
+      certificateIdentityRegexp: `^https://github.com/docker/actions-toolkit/.github/workflows/test.yml.*$`
+    });
+    expect(Object.keys(verifyResults).length).toEqual(2);
+  }, 100000);
+});
diff --git a/__tests__/sigstore/sigstore.test.itg.ts b/__tests__/sigstore/sigstore.test.itg.ts
index 6fff3f63..90483f32 100644
--- a/__tests__/sigstore/sigstore.test.itg.ts
+++ b/__tests__/sigstore/sigstore.test.itg.ts
@@ -38,7 +38,7 @@ jest.unmock('@actions/github');
 beforeAll(async () => {
   const cosignInstall = new CosignInstall();
   const cosignBinPath = await cosignInstall.download({
-    version: 'v3.0.2'
+    version: 'v3.0.4'
   });
   await cosignInstall.install(cosignBinPath);
 }, 100000);
diff --git a/src/sigstore/sigstore.ts b/src/sigstore/sigstore.ts
index 8c2b3e55..d8b899af 100644
--- a/src/sigstore/sigstore.ts
+++ b/src/sigstore/sigstore.ts
@@ -22,6 +22,7 @@ import * as core from '@actions/core';
 import {bundleFromJSON, bundleToJSON} from '@sigstore/bundle';
 import {Artifact, Bundle, CIContextProvider, DSSEBundleBuilder, FulcioSigner, RekorWitness, TSAWitness, Witness} from '@sigstore/sign';
 
+import {Context} from '../context';
 import {Cosign} from '../cosign/cosign';
 import {Exec} from '../exec';
 import {GitHub} from '../github';
@@ -73,6 +74,40 @@ export class Sigstore {
       core.info(`Using Sigstore signing endpoint: ${endpoints.fulcioURL}`);
       const noTransparencyLog = Sigstore.noTransparencyLog(opts.noTransparencyLog);
 
+      const cosignExtraArgs: string[] = [];
+      if (await this.cosign.versionSatisfies('>=3.0.4')) {
+        await core.group(`Creating Sigstore protobuf signing config`, async () => {
+          const signingConfig = Context.tmpName({
+            template: 'signing-config-XXXXXX.json',
+            tmpdir: Context.tmpDir()
+          });
+          // prettier-ignore
+          const createConfigArgs = [
+            'signing-config',
+            'create',
+            '--with-default-services=true',
+            `--out=${signingConfig}`
+          ];
+          if (noTransparencyLog) {
+            createConfigArgs.push('--no-default-rekor=true');
+          }
+          await Exec.exec('cosign', createConfigArgs, {
+            env: Object.assign({}, process.env, {
+              COSIGN_EXPERIMENTAL: '1'
+            }) as {
+              [key: string]: string;
+            }
+          });
+          core.info(JSON.stringify(JSON.parse(fs.readFileSync(signingConfig, {encoding: 'utf-8'})), null, 2));
+          cosignExtraArgs.push(`--signing-config=${signingConfig}`);
+        });
+      } else {
+        cosignExtraArgs.push('--use-signing-config');
+        if (noTransparencyLog) {
+          cosignExtraArgs.push('--tlog-upload=false');
+        }
+      }
+
       for (const imageName of opts.imageNames) {
         const attestationDigests = await this.imageTools.attestationDigests(`${imageName}@${opts.imageDigest}`);
         for (const attestationDigest of attestationDigests) {
@@ -85,11 +120,8 @@ export class Sigstore {
               '--oidc-provider', 'github-actions',
               '--registry-referrers-mode', 'oci-1-1',
               '--new-bundle-format',
-              '--use-signing-config'
+              ...cosignExtraArgs
             ];
-            if (noTransparencyLog) {
-              cosignArgs.push('--tlog-upload=false');
-            }
             core.info(`[command]cosign ${[...cosignArgs, attestationRef].join(' ')}`);
             const execRes = await Exec.getExecOutput('cosign', ['--verbose', ...cosignArgs, attestationRef], {
               ignoreReturnCode: true,