diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ff229d761..3357dae8c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -108,6 +108,8 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
 
       - name: Set up Node.js
         uses: actions/setup-node@v4
@@ -129,6 +131,9 @@ jobs:
       - name: Test heading variables
         run: npm run test:heading-vars
 
+      - name: Test sitemap lastmod
+        run: npm run test:sitemap-lastmod
+
       - name: Test tracking redirect middleware
         run: npm run test:tracking-redirect
 
diff --git a/astro.config.mjs b/astro.config.mjs
index deb71f7ca..0a9c57b38 100644
--- a/astro.config.mjs
+++ b/astro.config.mjs
@@ -4,7 +4,7 @@ import { defineConfig, envField } from 'astro/config';
 import remarkGfm from 'remark-gfm';
 import mermaid from 'astro-mermaid';
 import react from '@astrojs/react';
-import sitemap from '@astrojs/sitemap';
+import sitemap from './src/integrations/sitemap-lastmod.js';
 import starlight from '@astrojs/starlight';
 import starlightLlmsTxt from 'starlight-llms-txt';
 import starlightSidebarTopics from 'starlight-sidebar-topics';
diff --git a/package.json b/package.json
index 18983cd39..8efe7d82d 100644
--- a/package.json
+++ b/package.json
@@ -8,7 +8,7 @@
     "predev": "node scripts/generate-openapi-json.mjs",
     "build": "astro build",
     "postbuild": "node scripts/build-tracking-middleware.mjs",
-    "prebuild": "node scripts/generate-openapi-json.mjs",
+    "prebuild": "node scripts/ensure-git-history.mjs && node scripts/generate-openapi-json.mjs",
     "preview": "astro preview",
     "astro": "astro",
     "typecheck": "astro check",
@@ -24,6 +24,7 @@
     "test:kapa-webmcp": "node --test src/lib/kapa-webmcp.test.mjs",
     "test:kapa-support-escalation": "node --test src/lib/kapa-support-escalation.test.mjs",
     "test:homepage-json-ld": "node scripts/validate-homepage-json-ld.mjs",
+    "test:sitemap-lastmod": "node --test src/integrations/sitemap-lastmod.test.mjs src/lib/git-history.test.mjs",
     "postinstall": "patch-package"
   },
   "engines": {
diff --git a/scripts/ensure-git-history.mjs b/scripts/ensure-git-history.mjs
new file mode 100644
index 000000000..4ff811c4f
--- /dev/null
+++ b/scripts/ensure-git-history.mjs
@@ -0,0 +1,23 @@
+import { spawnSync } from 'node:child_process';
+import { performance } from 'node:perf_hooks';
+
+// A shallow boundary commit makes unchanged files look newly modified to
+// Starlight. Fetch history before Astro inlines git dates for pages/sitemaps.
+const shallow = spawnSync('git', ['rev-parse', '--is-shallow-repository'], { encoding: 'utf8' });
+if (shallow.status === 0 && shallow.stdout.trim() === 'true') {
+	const start = performance.now();
+	const origin = spawnSync('git', ['remote', 'get-url', 'origin'], { encoding: 'utf8' });
+	const { VERCEL_GIT_REPO_OWNER: owner, VERCEL_GIT_REPO_SLUG: slug } = process.env;
+	const publicRepo = owner && slug && /^[\w.-]+$/.test(owner) && /^[\w.-]+$/.test(slug)
+		? `https://github.com/${owner}/${slug}.git`
+		: undefined;
+	const remote = origin.status === 0 ? 'origin' : publicRepo;
+	const fetch = remote
+		? spawnSync('git', ['fetch', '--unshallow', '--no-tags', remote], { encoding: 'utf8', timeout: 120_000 })
+		: undefined;
+	if (fetch?.status === 0) {
+		console.log(`Fetched full git history in ${((performance.now() - start) / 1000).toFixed(1)}s.`);
+	} else {
+		console.warn('Could not restore full git history; shallow-boundary page dates will be omitted.');
+	}
+}
diff --git a/src/integrations/sitemap-lastmod.js b/src/integrations/sitemap-lastmod.js
new file mode 100644
index 000000000..44549f2b7
--- /dev/null
+++ b/src/integrations/sitemap-lastmod.js
@@ -0,0 +1,40 @@
+import sitemap from '@astrojs/sitemap';
+import { readFile } from 'node:fs/promises';
+import { fileURLToPath } from 'node:url';
+import path from 'node:path';
+import { parseHTML } from 'linkedom';
+
+export default function sitemapLastmod() {
+	let outputRoot;
+	const integration = sitemap({
+		serialize: async (item) => {
+			const pathname = decodeURIComponent(new URL(item.url).pathname);
+			const htmlPath = path.join(outputRoot, pathname, 'index.html');
+			try {
+				return withLastmod(item, await readFile(htmlPath, 'utf8'));
+			} catch (error) {
+				// Routes without generated HTML have no Starlight git date.
+				if (error.code === 'ENOENT' || error.code === 'ENOTDIR') return item;
+				throw error;
+			}
+		},
+	});
+	return {
+		...integration,
+		hooks: {
+			...integration.hooks,
+			// Runs before @astrojs/sitemap's build:done serialization, while
+			// the adapter still exposes the generated HTML directory.
+			'astro:build:generated': ({ dir }) => {
+				outputRoot = fileURLToPath(dir);
+			},
+		},
+	};
+}
+
+export function withLastmod(item, html) {
+	const { document } = parseHTML(html);
+	const value = document.querySelector('meta[property="article:modified_time"]')?.getAttribute('content');
+	if (!value || !Number.isFinite(Date.parse(value))) return item;
+	return { ...item, lastmod: new Date(value).toISOString() };
+}
diff --git a/src/integrations/sitemap-lastmod.test.mjs b/src/integrations/sitemap-lastmod.test.mjs
new file mode 100644
index 000000000..8ba4ca6b8
--- /dev/null
+++ b/src/integrations/sitemap-lastmod.test.mjs
@@ -0,0 +1,21 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { withLastmod } from './sitemap-lastmod.js';
+
+test('sitemap uses the exact rendered Starlight date, not build time', () => {
+	const item = { url: 'https://docs.warp.dev/factories/quickstart/' };
+	for (const date of ['2026-10-08T17:42:12.000Z', '2025-03-01T09:00:00.000Z']) {
+		assert.deepEqual(
+			withLastmod(item, `<meta property="article:modified_time" content="${date}">`),
+			{ ...item, lastmod: date },
+		);
+	}
+});
+
+test('pages without a valid Starlight date do not invent lastmod', () => {
+	const item = { url: 'https://docs.warp.dev/api/' };
+	for (const html of ['', '<time datetime="2026-10-09">A content example</time>',
+		'<meta property="article:modified_time" content="invalid">']) {
+		assert.equal(withLastmod(item, html), item);
+	}
+});
diff --git a/src/lib/git-history.js b/src/lib/git-history.js
new file mode 100644
index 000000000..7ed5a8bfb
--- /dev/null
+++ b/src/lib/git-history.js
@@ -0,0 +1,18 @@
+import { spawnSync } from 'node:child_process';
+import { readFileSync } from 'node:fs';
+
+// Boundary commits in a shallow checkout synthesize modifications for all
+// files at the clone horizon. Their timestamps are not content-change dates.
+export function getShallowBoundaryDates() {
+	const result = spawnSync('git', ['rev-parse', '--git-path', 'shallow'], { encoding: 'utf8' });
+	if (result.status !== 0) return new Set();
+	let commits;
+	try {
+		commits = readFileSync(result.stdout.trim(), 'utf8').trim().split('\n');
+	} catch {
+		return new Set();
+	}
+	if (!commits.every((commit) => /^[a-f0-9]{40,64}$/.test(commit))) return new Set();
+	const dates = spawnSync('git', ['show', '--no-patch', '--format=%ct', ...commits], { encoding: 'utf8' });
+	return new Set(dates.stdout.trim().split('\n').map((timestamp) => Number(timestamp) * 1000));
+}
diff --git a/src/lib/git-history.test.mjs b/src/lib/git-history.test.mjs
new file mode 100644
index 000000000..77c2b4509
--- /dev/null
+++ b/src/lib/git-history.test.mjs
@@ -0,0 +1,41 @@
+import assert from 'node:assert/strict';
+import { spawnSync } from 'node:child_process';
+import { mkdtempSync, readFileSync, unlinkSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import path from 'node:path';
+import test from 'node:test';
+import { getShallowBoundaryDates } from './git-history.js';
+
+test('unavailable history is nonfatal and boundary dates are identifiable', () => {
+	const root = process.cwd();
+	const repo = path.join(mkdtempSync(path.join(tmpdir(), 'docs-history-test-')), 'repo');
+	const init = spawnSync('git', ['init', repo], { encoding: 'utf8' });
+	assert.equal(init.status, 0, init.stderr);
+	const objects = spawnSync('git', ['rev-parse', '--git-path', 'objects'], { encoding: 'utf8' });
+	const head = spawnSync('git', ['rev-parse', 'HEAD'], { encoding: 'utf8' }).stdout.trim();
+	writeFileSync(path.join(repo, '.git/objects/info/alternates'), `${path.resolve(root, objects.stdout.trim())}\n`);
+	const git = (...args) => {
+		const result = spawnSync('git', args, { cwd: repo, encoding: 'utf8' });
+		assert.equal(result.status, 0, result.stderr);
+		return result.stdout.trim();
+	};
+	process.chdir(repo);
+	try {
+		git('update-ref', 'HEAD', head);
+		writeFileSync(path.join(repo, '.git/shallow'), `${head}\n`);
+		const timestamp = Number(git('show', '--no-patch', '--format=%ct', 'HEAD')) * 1000;
+		assert.deepEqual(getShallowBoundaryDates(), new Set([timestamp]));
+		const result = spawnSync('node', [path.join(root, 'scripts/ensure-git-history.mjs')], {
+			cwd: repo,
+			encoding: 'utf8',
+			env: { ...process.env, VERCEL_GIT_REPO_OWNER: '', VERCEL_GIT_REPO_SLUG: '' },
+		});
+		assert.equal(result.status, 0, result.stderr);
+		assert.match(result.stderr, /shallow-boundary page dates will be omitted/);
+		assert.ok(readFileSync(path.join(repo, '.git/shallow'), 'utf8').trim());
+		unlinkSync(path.join(repo, '.git/shallow'));
+		assert.deepEqual(getShallowBoundaryDates(), new Set());
+	} finally {
+		process.chdir(root);
+	}
+});
diff --git a/src/routeData.ts b/src/routeData.ts
index f5fc833a9..673114315 100644
--- a/src/routeData.ts
+++ b/src/routeData.ts
@@ -1,6 +1,9 @@
 import { defineRouteMiddleware } from '@astrojs/starlight/route-data';
 import config from 'virtual:starlight/user-config';
 import { getMarkdownPathFromHtmlPath } from './lib/docs-markdown.js';
+import { getShallowBoundaryDates } from './lib/git-history.js';
+
+const shallowBoundaryDates = getShallowBoundaryDates();
 
 /**
  * Per-page head augmentation.
@@ -15,7 +18,20 @@ import { getMarkdownPathFromHtmlPath } from './lib/docs-markdown.js';
  */
 export const onRequest = defineRouteMiddleware((context) => {
 	const route = context.locals.starlightRoute;
+	if (!(route.entry.data.lastUpdated instanceof Date) &&
+		route.lastUpdated && shallowBoundaryDates.has(route.lastUpdated.getTime())) {
+		route.lastUpdated = undefined;
+	}
 	const head = route.head;
+	// Reuse Starlight's git-derived date, including its frontmatter overrides.
+	// The sitemap serializer reads this from the generated page, so it never
+	// substitutes build time or guesses a source file from a URL.
+	if (route.lastUpdated) {
+		head.push({
+			tag: 'meta',
+			attrs: { property: 'article:modified_time', content: route.lastUpdated.toISOString() },
+		});
+	}
 
 	head.push({
 		tag: 'link',