diff --git a/next.config.js b/next.config.js
index 78d1da062..36b84a4f1 100644
--- a/next.config.js
+++ b/next.config.js
@@ -5,7 +5,7 @@ const nextConfig = {
         ignoreBuildErrors: true,
     },
     env: {
-        BUILD_ID: (process.env.GITHUB_SHA ?? '').slice(0, 7),
+        BUILD_VERSION: (process.env.GITHUB_SHA ?? '').slice(0, 7),
     },
 };
 
diff --git a/src/app/[spaceId]/(content)/layout.tsx b/src/app/[spaceId]/(content)/layout.tsx
index 17630f225..e09df154c 100644
--- a/src/app/[spaceId]/(content)/layout.tsx
+++ b/src/app/[spaceId]/(content)/layout.tsx
@@ -6,6 +6,7 @@ import React from 'react';
 import { AdminToolbar } from '@/components/AdminToolbar';
 import { CookiesToast } from '@/components/Cookies';
 import { SpaceLayout } from '@/components/SpaceLayout';
+import { buildVersion } from '@/lib/build';
 import { getContentSecurityPolicyNonce } from '@/lib/csp';
 import { absoluteHref, baseUrl } from '@/lib/links';
 import { shouldIndexSpace } from '@/lib/seo';
@@ -83,7 +84,7 @@ export async function generateMetadata({ params }: { params: SpaceParams }): Pro
 
     return {
         title: `${space.title}`,
-        generator: 'GitBook',
+        generator: `GitBook (${buildVersion()})`,
         // We pass `metadataBase` to avoid warnings from Next, but we still use absolute URLs
         // as metadataBase doesn't seem to work well on next-on-cloudflare.
         metadataBase: new URL(baseUrl()),
diff --git a/src/lib/api.ts b/src/lib/api.ts
index 8833a2002..e6818bb76 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -10,6 +10,7 @@ import {
 import assertNever from 'assert-never';
 import { headers } from 'next/headers';
 
+import { buildVersion } from './build';
 import { cache, cacheResponse, noCacheFetchOptions, parseCacheResponse } from './cache';
 
 export interface ContentPointer {
@@ -579,7 +580,7 @@ export function userAgent(): string {
         return process.env.GITBOOK_USER_AGENT;
     }
 
-    let result = `GitBook-Open/${process.env.BUILD_ID}`;
+    let result = `GitBook-Open/${buildVersion()}`;
     if (process.env.GITBOOK_USER_AGENT_COMMENT) {
         result += ` (${process.env.GITBOOK_USER_AGENT_COMMENT})`;
     }
diff --git a/src/lib/build.ts b/src/lib/build.ts
new file mode 100644
index 000000000..73dbcc4a5
--- /dev/null
+++ b/src/lib/build.ts
@@ -0,0 +1,6 @@
+/**
+ * Get a string representing the build version.
+ */
+export function buildVersion(): string {
+    return process.env.BUILD_VERSION || '0.0.0';
+}
diff --git a/src/middleware.ts b/src/middleware.ts
index d0713af32..423826744 100644
--- a/src/middleware.ts
+++ b/src/middleware.ts
@@ -13,6 +13,7 @@ import {
 } from '@/lib/api';
 import { createContentSecurityPolicyNonce, getContentSecurityPolicy } from '@/lib/csp';
 
+import { buildVersion } from './lib/build';
 import { getURLLookupAlternatives } from './lib/middleware';
 
 export const config = {
@@ -84,8 +85,11 @@ export async function middleware(request: NextRequest) {
         () => lookupSpaceForURL(mode, inputURL, visitorAuthToken),
     );
     if (!resolved) {
-        return new NextResponse(`Not found`, {
+        return new NextResponse(`Content not found`, {
             status: 404,
+            headers: {
+                'x-gitbook-version': buildVersion(),
+            },
         });
     }
 
@@ -149,6 +153,8 @@ export async function middleware(request: NextRequest) {
         },
     });
 
+    response.headers.set('x-gitbook-version', buildVersion());
+
     // Add Content Security Policy header
     response.headers.set('content-security-policy', csp);