diff --git a/.github/workflows/tests-pr.yml b/.github/workflows/tests-pr.yml
index 182fae6906..bd1a10446e 100644
--- a/.github/workflows/tests-pr.yml
+++ b/.github/workflows/tests-pr.yml
@@ -287,3 +287,53 @@ jobs:
           header: Type-diff
           message: ${{ steps.type-diff.outputs.report }}
           recreate: true
+
+  major-change-check:
+    if: github.event.pull_request.head.repo.full_name == github.repository
+    name: 'Breaking change detection'
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    outputs:
+      has_breaking_changes: ${{ steps.check.outputs.has_breaking_changes }}
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          repository: ${{ github.event.pull_request.head.repo.full_name || github.event.repository.full_name }}
+          ref: ${{ github.event.pull_request.head.ref || github.event.merge_group.head_ref }}
+          fetch-depth: 1
+      - name: Setup deps
+        uses: ./.github/actions/setup-cli-deps
+        with:
+          node-version: ${{ env.DEFAULT_NODE_VERSION }}
+      - name: Build
+        run: pnpm nx run-many --all --skip-nx-cache --target=build --output-style=stream
+      - name: Check for breaking changes
+        id: check
+        run: node workspace/src/major-change-check.js
+      - uses: marocchino/sticky-pull-request-comment@fcf6fe9e4a0409cd9316a5011435be0f3327f1e1 # v2.3.1
+        if: steps.check.outputs.has_breaking_changes == 'true'
+        with:
+          header: Breaking-change-detection
+          message: ${{ steps.check.outputs.report }}
+          recreate: true
+      - uses: marocchino/sticky-pull-request-comment@fcf6fe9e4a0409cd9316a5011435be0f3327f1e1 # v2.3.1
+        if: steps.check.outputs.has_breaking_changes != 'true'
+        with:
+          header: Breaking-change-detection
+          delete: true
+      - name: Fail if breaking changes detected
+        if: steps.check.outputs.has_breaking_changes == 'true'
+        run: |
+          echo '::error::Breaking changes detected. A member of @shopify/dev_experience must approve the breaking-change-approval environment.'
+          exit 1
+
+  major-change-approval:
+    name: 'Breaking change approval'
+    needs: major-change-check
+    if: always() && needs.major-change-check.outputs.has_breaking_changes == 'true'
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    environment: breaking-change-approval
+    steps:
+      - name: Approved
+        run: echo '✅ Breaking changes approved by dev_experience team member'
diff --git a/workspace/src/major-change-check.js b/workspace/src/major-change-check.js
new file mode 100644
index 0000000000..ef75f27858
--- /dev/null
+++ b/workspace/src/major-change-check.js
@@ -0,0 +1,375 @@
+#!/usr/bin/env node
+
+/**
+ * Detects potential breaking changes in a PR by checking:
+ *
+ * 1. Changesets requesting a major version bump
+ * 2. OCLIF manifest changes: removed commands, removed flags, or removed flag env vars
+ * 3. Zod schema changes: removed or renamed fields in app/extension config schemas
+ *
+ * Compares the current branch against the main branch baseline.
+ * Outputs a GitHub Actions summary and sets a `has_breaking_changes` output.
+ */
+
+import * as path from 'pathe'
+import * as url from 'url'
+import {mkdtemp, rm} from 'fs/promises'
+import os from 'os'
+import {promises as fs} from 'fs'
+import {setOutput} from '@actions/core'
+import {cloneCLIRepository} from './utils/git.js'
+import {logMessage, logSection} from './utils/log.js'
+import fg from 'fast-glob'
+
+const currentDirectory = path.join(url.fileURLToPath(new URL('.', import.meta.url)), '../..')
+
+// ---------------------------------------------------------------------------
+// 1. Check changesets for major bumps
+// ---------------------------------------------------------------------------
+
+async function checkChangesets() {
+  logSection('Checking changesets for major bumps')
+
+  const changesetFiles = await fg('.changeset/*.md', {
+    cwd: currentDirectory,
+    absolute: true,
+    ignore: ['**/README.md'],
+  })
+
+  const majorChangesets = []
+
+  for (const file of changesetFiles) {
+    const content = (await fs.readFile(file, 'utf-8')).trim()
+    // Changeset format: YAML frontmatter between --- markers, with 'package: major'
+    const frontmatterMatch = content.match(/^---\n([\s\S]*?)\n---/)
+    if (!frontmatterMatch) continue
+
+    const frontmatter = frontmatterMatch[1]
+    const lines = frontmatter.split('\n')
+
+    for (const line of lines) {
+      if (line.match(/:\s*major\s*$/)) {
+        majorChangesets.push({
+          file: path.basename(file),
+          line: line.trim(),
+        })
+      }
+    }
+  }
+
+  if (majorChangesets.length > 0) {
+    logMessage(`Found ${majorChangesets.length} changeset(s) with major bump`)
+    for (const cs of majorChangesets) {
+      logMessage(`  ${cs.file}: ${cs.line}`)
+    }
+  } else {
+    logMessage('No major changesets found')
+  }
+
+  return majorChangesets
+}
+
+// ---------------------------------------------------------------------------
+// 2. Check OCLIF manifest for removed commands, flags, or flag env vars
+// ---------------------------------------------------------------------------
+
+async function parseManifest(directory) {
+  const manifestPath = path.join(directory, 'packages/cli/oclif.manifest.json')
+  try {
+    const content = await fs.readFile(manifestPath, 'utf-8')
+    return JSON.parse(content)
+  } catch {
+    return null
+  }
+}
+
+function extractManifestSurface(manifest) {
+  const surface = {commands: {}, envVars: {}}
+  if (!manifest?.commands) return surface
+
+  for (const [cmdName, cmd] of Object.entries(manifest.commands)) {
+    const flags = {}
+    if (cmd.flags) {
+      for (const [flagName, flag] of Object.entries(cmd.flags)) {
+        flags[flagName] = {
+          type: flag.type,
+          env: flag.env || null,
+        }
+        if (flag.env) {
+          surface.envVars[flag.env] = surface.envVars[flag.env] || []
+          surface.envVars[flag.env].push({command: cmdName, flag: flagName})
+        }
+      }
+    }
+    surface.commands[cmdName] = {flags}
+  }
+
+  return surface
+}
+
+async function checkManifest(baselineDirectory) {
+  logSection('Checking OCLIF manifest for removed commands/flags')
+
+  const baselineManifest = await parseManifest(baselineDirectory)
+  const currentManifest = await parseManifest(currentDirectory)
+
+  if (!baselineManifest || !currentManifest) {
+    logMessage('Could not read one or both manifests, skipping')
+    return {removedCommands: [], removedFlags: [], removedEnvVars: []}
+  }
+
+  const baseline = extractManifestSurface(baselineManifest)
+  const current = extractManifestSurface(currentManifest)
+
+  // Removed commands
+  const removedCommands = Object.keys(baseline.commands).filter(
+    (cmd) => !current.commands[cmd],
+  )
+
+  // Removed flags (in commands that still exist)
+  const removedFlags = []
+  for (const [cmdName, cmd] of Object.entries(baseline.commands)) {
+    if (!current.commands[cmdName]) continue
+    for (const flagName of Object.keys(cmd.flags)) {
+      if (!current.commands[cmdName].flags[flagName]) {
+        removedFlags.push({command: cmdName, flag: flagName})
+      }
+    }
+  }
+
+  // Removed env vars
+  const removedEnvVars = []
+  for (const [envVar, usages] of Object.entries(baseline.envVars)) {
+    if (!current.envVars[envVar]) {
+      removedEnvVars.push({envVar, usages})
+    }
+  }
+
+  if (removedCommands.length > 0) {
+    logMessage(`Removed commands: ${removedCommands.join(', ')}`)
+  }
+  if (removedFlags.length > 0) {
+    logMessage(`Removed flags: ${removedFlags.map((f) => `${f.command} --${f.flag}`).join(', ')}`)
+  }
+  if (removedEnvVars.length > 0) {
+    logMessage(`Removed env vars: ${removedEnvVars.map((e) => e.envVar).join(', ')}`)
+  }
+  if (removedCommands.length === 0 && removedFlags.length === 0 && removedEnvVars.length === 0) {
+    logMessage('No removed commands, flags, or env vars')
+  }
+
+  return {removedCommands, removedFlags, removedEnvVars}
+}
+
+// ---------------------------------------------------------------------------
+// 3. Check Zod schemas for removed/renamed fields
+// ---------------------------------------------------------------------------
+
+/**
+ * Extracts a simplified map of schema field names from Zod schema source files.
+ * Looks for patterns like: `fieldName: zod.` or `field_name: zod.` in .object({...}) blocks.
+ * This is an intentionally conservative heuristic — AST parsing would be heavier.
+ */
+function extractSchemaFields(content) {
+  const fields = new Set()
+
+  // Match zod.object({ ... }) blocks and extract field names
+  // Handles multi-line objects
+  const objectBlockRegex = /\.object\(\s*\{([\s\S]*?)\}\s*\)/g
+  let match
+
+  while ((match = objectBlockRegex.exec(content)) !== null) {
+    const block = match[1]
+    // Extract field names: word characters (including underscore) before a colon
+    const fieldRegex = /^\s*(\w+)\s*:/gm
+    let fieldMatch
+    while ((fieldMatch = fieldRegex.exec(block)) !== null) {
+      fields.add(fieldMatch[1])
+    }
+  }
+
+  return fields
+}
+
+async function checkSchemas(baselineDirectory) {
+  logSection('Checking Zod schemas for removed fields')
+
+  const schemaGlob = 'packages/app/src/cli/models/**/specifications/**/*.ts'
+  const appModelGlob = 'packages/app/src/cli/models/app/app.ts'
+  const ignorePatterns = ['**/*.test.ts', '**/*.test-data.ts']
+
+  const currentSchemaFiles = await fg([schemaGlob, appModelGlob], {
+    cwd: currentDirectory,
+    ignore: ignorePatterns,
+  })
+  const baselineSchemaFiles = await fg([schemaGlob, appModelGlob], {
+    cwd: baselineDirectory,
+    ignore: ignorePatterns,
+  })
+
+  const removedFields = []
+
+  for (const file of baselineSchemaFiles) {
+    const baselinePath = path.join(baselineDirectory, file)
+    const currentPath = path.join(currentDirectory, file)
+
+    let baselineContent
+    let currentContent
+    try {
+      baselineContent = await fs.readFile(baselinePath, 'utf-8')
+    } catch {
+      continue
+    }
+    try {
+      currentContent = await fs.readFile(currentPath, 'utf-8')
+    } catch {
+      // File was deleted — all fields are removed
+      const fields = extractSchemaFields(baselineContent)
+      if (fields.size > 0) {
+        removedFields.push({file, fields: [...fields], type: 'file_deleted'})
+      }
+      continue
+    }
+
+    // Only check files that actually contain zod schemas
+    if (!baselineContent.includes('zod.object(') && !baselineContent.includes('.object(')) continue
+
+    const baselineFields = extractSchemaFields(baselineContent)
+    const currentFields = extractSchemaFields(currentContent)
+
+    const removed = [...baselineFields].filter((f) => !currentFields.has(f))
+    if (removed.length > 0) {
+      removedFields.push({file, fields: removed, type: 'fields_removed'})
+    }
+  }
+
+  if (removedFields.length > 0) {
+    for (const entry of removedFields) {
+      logMessage(`${entry.file}: removed fields [${entry.fields.join(', ')}] (${entry.type})`)
+    }
+  } else {
+    logMessage('No removed schema fields detected')
+  }
+
+  return removedFields
+}
+
+// ---------------------------------------------------------------------------
+// Report
+// ---------------------------------------------------------------------------
+
+function buildReport({majorChangesets, manifestChanges, schemaChanges}) {
+  const hasBreaking =
+    majorChangesets.length > 0 ||
+    manifestChanges.removedCommands.length > 0 ||
+    manifestChanges.removedFlags.length > 0 ||
+    manifestChanges.removedEnvVars.length > 0 ||
+    schemaChanges.length > 0
+
+  if (!hasBreaking) {
+    return null
+  }
+
+  let report = `## ⚠️ Potential Breaking Changes Detected
+
+This PR contains changes that may break the existing contract.
+
+**@shopify/dev_experience** — this PR contains breaking changes that require coordination for the next major release. This check will remain failed until a member of the team approves the workflow run.
+
+> 💬 Head to [#help-dev-platform](https://shopify.enterprise.slack.com/archives/C07UJ7UNMTK) to discuss timing and plan the release.
+
+`
+
+  if (majorChangesets.length > 0) {
+    report += `### 📦 Major Version Changesets
+The following changesets request a **major** version bump:
+
+| Changeset | Package |
+|-----------|---------|
+`
+    for (const cs of majorChangesets) {
+      report += `| \`${cs.file}\` | ${cs.line} |\n`
+    }
+    report += '\n'
+  }
+
+  if (manifestChanges.removedCommands.length > 0) {
+    report += `### 🗑️ Removed Commands
+The following commands were removed from the OCLIF manifest:
+
+${manifestChanges.removedCommands.map((cmd) => `- \`${cmd}\``).join('\n')}
+
+`
+  }
+
+  if (manifestChanges.removedFlags.length > 0) {
+    report += `### 🏳️ Removed Flags
+The following flags were removed from existing commands:
+
+| Command | Flag |
+|---------|------|
+`
+    for (const f of manifestChanges.removedFlags) {
+      report += `| \`${f.command}\` | \`--${f.flag}\` |\n`
+    }
+    report += '\n'
+  }
+
+  if (manifestChanges.removedEnvVars.length > 0) {
+    report += `### 🔧 Removed Environment Variables
+The following env vars are no longer referenced in command flags:
+
+| Env Var | Previously Used By |
+|---------|-------------------|
+`
+    for (const e of manifestChanges.removedEnvVars) {
+      const usages = e.usages.map((u) => `\`${u.command} --${u.flag}\``).join(', ')
+      report += `| \`${e.envVar}\` | ${usages} |\n`
+    }
+    report += '\n'
+  }
+
+  if (schemaChanges.length > 0) {
+    report += `### 📝 Removed Schema Fields
+The following Zod schema fields were removed or their files deleted:
+
+| File | Removed Fields | Reason |
+|------|---------------|--------|
+`
+    for (const entry of schemaChanges) {
+      const fields = entry.fields.map((f) => `\`${f}\``).join(', ')
+      const reason = entry.type === 'file_deleted' ? 'File deleted' : 'Fields removed'
+      report += `| \`${entry.file}\` | ${fields} | ${reason} |\n`
+    }
+    report += '\n'
+  }
+
+  return report
+}
+
+// ---------------------------------------------------------------------------
+// Main
+// ---------------------------------------------------------------------------
+
+const tmpDir = await mkdtemp(path.join(os.tmpdir(), 'major-change-check-'))
+
+try {
+  const baselineDirectory = await cloneCLIRepository(tmpDir)
+
+  const majorChangesets = await checkChangesets()
+  const manifestChanges = await checkManifest(baselineDirectory)
+  const schemaChanges = await checkSchemas(baselineDirectory)
+
+  const report = buildReport({majorChangesets, manifestChanges, schemaChanges})
+
+  if (report) {
+    logSection('\n⚠️  Breaking changes detected!')
+    setOutput('has_breaking_changes', 'true')
+    setOutput('report', report)
+  } else {
+    logSection('\n✅ No breaking changes detected')
+    setOutput('has_breaking_changes', 'false')
+  }
+} finally {
+  await rm(tmpDir, {recursive: true, force: true, maxRetries: 2})
+}