diff --git a/frontend/src/components/ChatHeader.test.tsx b/frontend/src/components/ChatHeader.test.tsx
index 454afc9..72f6f98 100644
--- a/frontend/src/components/ChatHeader.test.tsx
+++ b/frontend/src/components/ChatHeader.test.tsx
@@ -131,6 +131,11 @@ describe("ChatHeader", () => {
 		expect(onToggleTools).toHaveBeenCalled();
 	});
 
+	it("displays the build timestamp in human-readable format", () => {
+		render(<ChatHeader {...makeProps()} />);
+		expect(screen.getByText("Built: 2026-01-01 00:00")).toBeInTheDocument();
+	});
+
 	it("shows disabled placeholder when claudeModels is empty and no API key", () => {
 		render(
 			<ChatHeader
diff --git a/frontend/src/components/ChatHeader.tsx b/frontend/src/components/ChatHeader.tsx
index 59b9289..bcad118 100644
--- a/frontend/src/components/ChatHeader.tsx
+++ b/frontend/src/components/ChatHeader.tsx
@@ -1,3 +1,13 @@
+function formatBuildTime(isoString: string): string {
+	const d = new Date(isoString);
+	const year = d.getUTCFullYear();
+	const month = String(d.getUTCMonth() + 1).padStart(2, "0");
+	const day = String(d.getUTCDate()).padStart(2, "0");
+	const hours = String(d.getUTCHours()).padStart(2, "0");
+	const minutes = String(d.getUTCMinutes()).padStart(2, "0");
+	return `Built: ${year}-${month}-${day} ${hours}:${minutes}`;
+}
+
 interface ContextUsage {
 	used: number;
 	total: number;
@@ -109,6 +119,18 @@ export function ChatHeader({
 			</div>
 
 			<div style={{ display: "flex", alignItems: "center", gap: "16px" }}>
+				<div
+					style={{
+						fontSize: "0.75em",
+						color: "#555",
+						whiteSpace: "nowrap",
+						fontFamily: "monospace",
+					}}
+					title={__BUILD_TIME__}
+				>
+					{formatBuildTime(__BUILD_TIME__)}
+				</div>
+
 				<div
 					style={{
 						fontSize: "0.9em",
diff --git a/frontend/src/vite-env.d.ts b/frontend/src/vite-env.d.ts
index 41c9893..363ea5c 100644
--- a/frontend/src/vite-env.d.ts
+++ b/frontend/src/vite-env.d.ts
@@ -1,5 +1,9 @@
 /// <reference types="vite/client" />
 
+declare global {
+	const __BUILD_TIME__: string;
+}
+
 declare module "react" {
 	interface InputHTMLAttributes<T> {
 		webkitdirectory?: string;
diff --git a/frontend/vite.config.ts b/frontend/vite.config.ts
index 37e2e17..8d968f9 100644
--- a/frontend/vite.config.ts
+++ b/frontend/vite.config.ts
@@ -8,6 +8,7 @@ export default defineConfig(() => {
     plugins: [react()],
     define: {
       __STORYKIT_PORT__: JSON.stringify(String(backendPort)),
+      __BUILD_TIME__: JSON.stringify(new Date().toISOString()),
     },
     server: {
       port: backendPort + 2172,
diff --git a/frontend/vitest.config.ts b/frontend/vitest.config.ts
index 633dc71..3cfc5ab 100644
--- a/frontend/vitest.config.ts
+++ b/frontend/vitest.config.ts
@@ -3,6 +3,9 @@ import { defineConfig } from "vitest/config";
 
 export default defineConfig({
   plugins: [react()],
+  define: {
+    __BUILD_TIME__: JSON.stringify("2026-01-01T00:00:00.000Z"),
+  },
   test: {
     environment: "jsdom",
     globals: true,