diff --git a/.github/changeset-preview/action.yml b/.github/changeset-preview/action.yml
new file mode 100644
index 00000000..8a32dde8
--- /dev/null
+++ b/.github/changeset-preview/action.yml
@@ -0,0 +1,18 @@
+name: Changeset Preview
+description: Generates comment on a PR showing expected version impact
+runs:
+  using: composite
+  steps:
+    - name: Preview version bumps
+      shell: bash
+      run: node ${{ github.action_path }}/preview-changeset-versions.mjs --output /tmp/changeset-preview.md
+    - name: Post PR comment
+      shell: bash
+      run: |
+        node ${{ github.action_path }}/upsert-pr-comment.mjs \
+          --pr "${{ github.event.number }}" \
+          --body-file /tmp/changeset-preview.md \
+          --marker "<!-- changeset-version-preview -->"
+      env:
+        REPOSITORY: ${{ github.repository }}
+        GH_TOKEN: ${{ github.token }}
diff --git a/.github/changeset-preview/preview-changeset-versions.mjs b/.github/changeset-preview/preview-changeset-versions.mjs
new file mode 100644
index 00000000..3f85842f
--- /dev/null
+++ b/.github/changeset-preview/preview-changeset-versions.mjs
@@ -0,0 +1,197 @@
+#!/usr/bin/env node
+
+/**
+ * Preview the version bumps that `changeset version` will produce.
+ *
+ * Workflow:
+ *   1. Snapshot every workspace package's current version
+ *   2. Run `changeset version` (mutates package.json files)
+ *   3. Diff against the snapshot
+ *   4. Print a markdown summary (or write to --output file)
+ *
+ * This script is meant to run in CI on a disposable checkout — it does NOT
+ * revert the changes it makes.
+ */
+
+import { execSync } from 'node:child_process'
+import { readdirSync, readFileSync, writeFileSync } from 'node:fs'
+import { join, resolve } from 'node:path'
+import { parseArgs } from 'node:util'
+
+const ROOT = resolve(import.meta.dirname, '..', '..')
+
+const PACKAGES_DIR = join(ROOT, 'packages')
+
+function readPackageVersions() {
+  const versions = new Map()
+  for (const dir of readdirSync(PACKAGES_DIR, { withFileTypes: true })) {
+    if (!dir.isDirectory()) continue
+    const pkgPath = join(PACKAGES_DIR, dir.name, 'package.json')
+    try {
+      const pkg = JSON.parse(readFileSync(pkgPath, 'utf8'))
+      if (pkg.name && pkg.version && pkg.private !== true) {
+        versions.set(pkg.name, pkg.version)
+      }
+    } catch {
+      // skip packages without a valid package.json
+    }
+  }
+  return versions
+}
+
+function readChangesetEntries() {
+  const changesetDir = join(ROOT, '.changeset')
+  const explicit = new Map()
+  for (const file of readdirSync(changesetDir)) {
+    if (file === 'config.json' || file === 'README.md' || !file.endsWith('.md'))
+      continue
+    const content = readFileSync(join(changesetDir, file), 'utf8')
+    const frontmatterMatch = content.match(/^---\n([\s\S]*?)\n---/)
+    if (!frontmatterMatch) continue
+    for (const line of frontmatterMatch[1].split('\n')) {
+      const match = line.match(/^['"]?([^'"]+)['"]?\s*:\s*(major|minor|patch)/)
+      if (match) {
+        const [, name, bump] = match
+        const existing = explicit.get(name)
+        // keep the highest bump if a package appears in multiple changesets
+        if (!existing || bumpRank(bump) > bumpRank(existing)) {
+          explicit.set(name, bump)
+        }
+      }
+    }
+  }
+  return explicit
+}
+
+function bumpRank(bump) {
+  return bump === 'major' ? 3 : bump === 'minor' ? 2 : 1
+}
+
+function bumpType(oldVersion, newVersion) {
+  const [oMaj, oMin] = oldVersion.split('.').map(Number)
+  const [nMaj, nMin] = newVersion.split('.').map(Number)
+  if (nMaj > oMaj) return 'major'
+  if (nMin > oMin) return 'minor'
+  return 'patch'
+}
+
+function main() {
+  const { values } = parseArgs({
+    args: process.argv.slice(2),
+    options: {
+      output: { type: 'string', short: 'o' },
+    },
+    strict: true,
+    allowPositionals: false,
+  })
+
+  // 1. Read explicit changeset entries
+  const explicit = readChangesetEntries()
+
+  if (explicit.size === 0) {
+    const msg = 'No changeset entries found — nothing to preview.\n'
+    if (values.output) {
+      writeFileSync(values.output, msg)
+    } else {
+      process.stdout.write(msg)
+    }
+    return
+  }
+
+  // 2. Snapshot current versions
+  const before = readPackageVersions()
+
+  // 3. Temporarily swap changeset config to skip changelog generation
+  //    (the GitHub changelog plugin requires a token we don't need for previews)
+  const configPath = join(ROOT, '.changeset', 'config.json')
+  const originalConfig = readFileSync(configPath, 'utf8')
+  try {
+    const config = JSON.parse(originalConfig)
+    config.changelog = false
+    writeFileSync(configPath, JSON.stringify(config, null, 2))
+
+    // 4. Run changeset version
+    execSync('pnpm changeset version', { cwd: ROOT, stdio: 'pipe' })
+  } finally {
+    // Always restore the original config
+    writeFileSync(configPath, originalConfig)
+  }
+
+  // 5. Read new versions
+  const after = readPackageVersions()
+
+  // 6. Diff
+  const bumps = []
+  for (const [name, newVersion] of after) {
+    const oldVersion = before.get(name)
+    if (!oldVersion || oldVersion === newVersion) continue
+    const bump = bumpType(oldVersion, newVersion)
+    const source = explicit.has(name) ? explicit.get(name) : 'dependency'
+    bumps.push({ name, oldVersion, newVersion, bump, source })
+  }
+
+  // Sort: major first, then minor, then patch; within each group alphabetical
+  bumps.sort(
+    (a, b) =>
+      bumpRank(b.bump) - bumpRank(a.bump) || a.name.localeCompare(b.name),
+  )
+
+  // 7. Build markdown
+  const lines = []
+  lines.push('<!-- changeset-version-preview -->')
+  lines.push('## Changeset Version Preview')
+  lines.push('')
+
+  if (bumps.length === 0) {
+    lines.push('No version changes detected.')
+  } else {
+    const explicitBumps = bumps.filter((b) => b.source !== 'dependency')
+    const dependencyBumps = bumps.filter((b) => b.source === 'dependency')
+
+    lines.push(
+      `**${explicitBumps.length}** package(s) bumped directly, **${dependencyBumps.length}** bumped as dependents.`,
+    )
+    lines.push('')
+
+    if (explicitBumps.length > 0) {
+      lines.push('### Direct bumps')
+      lines.push('')
+      lines.push('| Package | Bump | Version |')
+      lines.push('| --- | --- | --- |')
+      for (const b of explicitBumps) {
+        lines.push(
+          `| \`${b.name}\` | **${b.bump}** | ${b.oldVersion} → ${b.newVersion} |`,
+        )
+      }
+      lines.push('')
+    }
+
+    if (dependencyBumps.length > 0) {
+      lines.push(
+        '<details>',
+        `<summary>Dependency bumps (${dependencyBumps.length})</summary>`,
+        '',
+        '| Package | Bump | Version |',
+        '| --- | --- | --- |',
+      )
+      for (const b of dependencyBumps) {
+        lines.push(
+          `| \`${b.name}\` | ${b.bump} | ${b.oldVersion} → ${b.newVersion} |`,
+        )
+      }
+      lines.push('', '</details>')
+    }
+  }
+
+  lines.push('')
+
+  const md = lines.join('\n')
+  if (values.output) {
+    writeFileSync(values.output, md)
+    process.stdout.write(`Written to ${values.output}\n`)
+  } else {
+    process.stdout.write(md)
+  }
+}
+
+main()
diff --git a/.github/changeset-preview/upsert-pr-comment.mjs b/.github/changeset-preview/upsert-pr-comment.mjs
new file mode 100644
index 00000000..9637e213
--- /dev/null
+++ b/.github/changeset-preview/upsert-pr-comment.mjs
@@ -0,0 +1,159 @@
+#!/usr/bin/env node
+
+import { promises as fsp } from 'node:fs'
+import path from 'node:path'
+import { parseArgs as parseNodeArgs } from 'node:util'
+
+const DEFAULT_MARKER = '<!-- bundle-size-benchmark -->'
+
+function parseArgs(argv) {
+  const { values } = parseNodeArgs({
+    args: argv,
+    allowPositionals: false,
+    strict: true,
+    options: {
+      pr: { type: 'string' },
+      'body-file': { type: 'string' },
+      repo: { type: 'string' },
+      token: { type: 'string' },
+      marker: { type: 'string' },
+      'api-url': { type: 'string' },
+    },
+  })
+
+  const args = {
+    pr: values.pr ? Number.parseInt(values.pr, 10) : undefined,
+    bodyFile: values['body-file'],
+    repo: values.repo ?? process.env.GITHUB_REPOSITORY,
+    marker: values.marker ?? DEFAULT_MARKER,
+    token: values.token ?? (process.env.GITHUB_TOKEN || process.env.GH_TOKEN),
+    apiUrl:
+      values['api-url'] ??
+      (process.env.GITHUB_API_URL || 'https://api.github.com'),
+  }
+
+  if (!Number.isFinite(args.pr) || args.pr <= 0) {
+    throw new Error('Missing required argument: --pr')
+  }
+
+  if (!args.bodyFile) {
+    throw new Error('Missing required argument: --body-file')
+  }
+
+  if (!args.repo || !args.repo.includes('/')) {
+    throw new Error(
+      'Missing repository context. Provide --repo or GITHUB_REPOSITORY.',
+    )
+  }
+
+  if (!args.token) {
+    throw new Error('Missing token. Provide --token or GITHUB_TOKEN.')
+  }
+
+  return args
+}
+
+async function githubRequest({ apiUrl, token, method, endpoint, body }) {
+  const url = `${apiUrl.replace(/\/$/, '')}${endpoint}`
+  const response = await fetch(url, {
+    method,
+    headers: {
+      Authorization: `Bearer ${token}`,
+      Accept: 'application/vnd.github+json',
+      'User-Agent': 'tanstack-router-bundle-size-bot',
+      'Content-Type': 'application/json',
+    },
+    body: body ? JSON.stringify(body) : undefined,
+  })
+
+  if (!response.ok) {
+    const text = await response.text()
+    throw new Error(
+      `${method} ${endpoint} failed (${response.status} ${response.statusText}): ${text}`,
+    )
+  }
+
+  if (response.status === 204) {
+    return undefined
+  }
+
+  return response.json()
+}
+
+async function listIssueComments({ apiUrl, token, repo, pr }) {
+  const comments = []
+  let page = 1
+  const perPage = 100
+
+  for (;;) {
+    const data = await githubRequest({
+      apiUrl,
+      token,
+      method: 'GET',
+      endpoint: `/repos/${repo}/issues/${pr}/comments?per_page=${perPage}&page=${page}`,
+    })
+
+    comments.push(...data)
+
+    if (!Array.isArray(data) || data.length < perPage) {
+      break
+    }
+
+    page += 1
+  }
+
+  return comments
+}
+
+async function main() {
+  const args = parseArgs(process.argv.slice(2))
+  const bodyPath = path.resolve(args.bodyFile)
+  const rawBody = await fsp.readFile(bodyPath, 'utf8')
+  const body = rawBody.includes(args.marker)
+    ? rawBody
+    : `${args.marker}\n${rawBody}`
+
+  const comments = await listIssueComments({
+    apiUrl: args.apiUrl,
+    token: args.token,
+    repo: args.repo,
+    pr: args.pr,
+  })
+
+  const existing = comments.find(
+    (comment) =>
+      typeof comment?.body === 'string' && comment.body.includes(args.marker),
+  )
+
+  if (existing) {
+    await githubRequest({
+      apiUrl: args.apiUrl,
+      token: args.token,
+      method: 'PATCH',
+      endpoint: `/repos/${args.repo}/issues/comments/${existing.id}`,
+      body: { body },
+    })
+
+    process.stdout.write(
+      `Updated PR #${args.pr} bundle-size comment (${existing.id}).\n`,
+    )
+    return
+  }
+
+  const created = await githubRequest({
+    apiUrl: args.apiUrl,
+    token: args.token,
+    method: 'POST',
+    endpoint: `/repos/${args.repo}/issues/${args.pr}/comments`,
+    body: { body },
+  })
+
+  process.stdout.write(
+    `Created PR #${args.pr} bundle-size comment (${created?.id ?? 'unknown'}).\n`,
+  )
+}
+
+main().catch((error) => {
+  console.error(error)
+  process.exit(1)
+})
diff --git a/.github/workflows/changeset-preview.yml b/.github/workflows/changeset-preview.yml
new file mode 100644
index 00000000..3eb706ed
--- /dev/null
+++ b/.github/workflows/changeset-preview.yml
@@ -0,0 +1,26 @@
+name: Changeset Preview
+
+on:
+  pull_request:
+    paths:
+      - '.changeset/**'
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.number || github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  preview:
+    name: Version Preview
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6.0.1
+      - name: Setup Tools
+        uses: tanstack/config/.github/setup@main
+      - name: Changeset Preview
+        uses: ./.github/changeset-preview