diff --git a/actions/setup/js/generate_aw_info.cjs b/actions/setup/js/generate_aw_info.cjs
index a8d266a0328..89b97a6ff5a 100644
--- a/actions/setup/js/generate_aw_info.cjs
+++ b/actions/setup/js/generate_aw_info.cjs
@@ -9,6 +9,7 @@ const { validateContextVariables } = require("./validate_context_variables.cjs")
 const validateLockdownRequirements = require("./validate_lockdown_requirements.cjs");
 const { writeMergedModelsJSON } = require("./merge_frontmatter_models.cjs");
 const { getErrorMessage } = require("./error_helpers.cjs");
+const { ERR_CONFIG } = require("./error_codes.cjs");
 
 /**
  * Generate aw_info.json with workflow run metadata.
@@ -52,11 +53,23 @@ async function main(core, ctx) {
   }
 
   // Build awInfo from env vars (compile-time) + context (runtime)
+  const model = process.env.GH_AW_INFO_MODEL || "";
+
+  // Reject model names that contain an unresolved GitHub Actions expression.
+  // This can happen when a vars.* expression was used for the model in the
+  // workflow frontmatter but the variable is not defined in the repository,
+  // causing GitHub Actions to pass the literal expression string at runtime.
+  if (/\$\{\{/.test(model)) {
+    const message = `${ERR_CONFIG}: GH_AW_INFO_MODEL contains an unresolved GitHub Actions expression: ${JSON.stringify(model)}`;
+    core.setFailed(message);
+    throw new Error(message);
+  }
+
   /** @type {Record<string, unknown>} */
   const awInfo = {
     engine_id: process.env.GH_AW_INFO_ENGINE_ID || "",
     engine_name: process.env.GH_AW_INFO_ENGINE_NAME || "",
-    model: process.env.GH_AW_INFO_MODEL || "",
+    model,
     version: process.env.GH_AW_INFO_VERSION || "",
     agent_version: process.env.GH_AW_INFO_AGENT_VERSION || "",
     workflow_name: process.env.GH_AW_INFO_WORKFLOW_NAME || "",
diff --git a/actions/setup/js/generate_aw_info.test.cjs b/actions/setup/js/generate_aw_info.test.cjs
index 489590169fe..c0721ecc26d 100644
--- a/actions/setup/js/generate_aw_info.test.cjs
+++ b/actions/setup/js/generate_aw_info.test.cjs
@@ -230,6 +230,57 @@ describe("generate_aw_info.cjs", () => {
     expect(awInfo.steps.firewall).toBe("squid");
   });
 
+  it("should fail when model name contains an unresolved GitHub Actions expression", async () => {
+    process.env.GH_AW_INFO_MODEL = "${{ vars.COPILOT_MODEL }}";
+
+    await expect(main(mockCore, mockContext)).rejects.toThrow("ERR_CONFIG");
+    expect(mockCore.setFailed).toHaveBeenCalledWith(expect.stringContaining("ERR_CONFIG"));
+    expect(mockCore.setFailed).toHaveBeenCalledWith(expect.stringContaining("unresolved GitHub Actions expression"));
+    expect(mockCore.setFailed).toHaveBeenCalledWith(expect.stringContaining(JSON.stringify("${{ vars.COPILOT_MODEL }}")));
+  });
+
+  it("should fail when model name contains a partial unresolved expression", async () => {
+    process.env.GH_AW_INFO_MODEL = "${{ vars.MODEL || 'gpt-4' }}";
+
+    await expect(main(mockCore, mockContext)).rejects.toThrow("ERR_CONFIG");
+    expect(mockCore.setFailed).toHaveBeenCalledWith(expect.stringContaining("ERR_CONFIG"));
+  });
+
+  it("should not fail when model name does not contain unresolved expressions", async () => {
+    const cases = [
+      { label: "plain string", model: "gpt-4o" },
+      { label: "empty string", model: "" },
+    ];
+
+    for (const { label, model } of cases) {
+      process.env.GH_AW_INFO_MODEL = model;
+
+      try {
+        await main(mockCore, mockContext);
+
+        expect(mockCore.setFailed).not.toHaveBeenCalled();
+        const awInfo = JSON.parse(fs.readFileSync(awInfoPath, "utf8"));
+        expect(awInfo.model).toBe(model);
+      } catch (error) {
+        throw new Error(`${label} case failed: ${error instanceof Error ? error.message : String(error)}`);
+      }
+    }
+  });
+
+  it("should not fail when model is a resolved experiment variant string", async () => {
+    // Workflows using experiment variants set model to a GitHub Actions expression in frontmatter
+    // (e.g. model: "${{ needs.activation.outputs.model_size }}").  GitHub Actions evaluates
+    // that expression before passing the value as an environment variable, so by the time
+    // generate_aw_info.cjs runs, GH_AW_INFO_MODEL holds the resolved variant string.
+    process.env.GH_AW_INFO_MODEL = "claude-haiku-4.5";
+
+    await main(mockCore, mockContext);
+
+    expect(mockCore.setFailed).not.toHaveBeenCalled();
+    const awInfo = JSON.parse(fs.readFileSync(awInfoPath, "utf8"));
+    expect(awInfo.model).toBe("claude-haiku-4.5");
+  });
+
   it("should fail when a numeric context field contains non-numeric data", async () => {
     const maliciousContext = {
       ...mockContext,