Using Zod 4 results in cryptic TypeError during runtime

[mjakl]

Stagehand (I'm using version 2.4.2) is not working with Zod 4, running the example from the quickstart with Zod 4 results in this error:

Full error:
schema._def.shape is not a function
    at StagehandAPI.<anonymous> (.../node_modules/@browserbasehq/stagehand/dist/index.js:4550:23)
    at Generator.next (<anonymous>)
    at fulfilled (.../node_modules/@browserbasehq/stagehand/dist/index.js:66:24)
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)

Workaround: Falling back to Zod ^3 resolves the problem.

---

More detailed error output:

 StagehandResponseParseError  Failed to parse server response, StagehandResponseParseError
error stack:
  • index.js	StagehandAPI.<anonymous>
	/node_modules/@browserbasehq/stagehand/dist/index.js:4560
  •

  • index.js	fulfilled
	/node_modules/@browserbasehq/stagehand/dist/index.js:66
  • task_queues	process.processTicksAndRejections
	internal/process/task_queues:105
[2025-08-03 17:32:36.228 +0200] INFO: running extract
    category: "extract"
    instruction: "extract the main heading of the page"
    requestId: "5krxa0u1zc"
    modelName: "claude-sonnet-4-20250514"
[2025-08-03 17:32:36.228 +0200] INFO: starting extraction using a11y tree
    category: "extraction"
    instruction: "extract the main heading of the page"
[2025-08-03 17:32:36.906 +0200] INFO: got accessibility tree in 8 ms
    category: "observation"
[2025-08-03 17:32:36.906 +0200] INFO: Got accessibility tree data
    category: "extraction"
[2025-08-03 17:32:36.906 +0200] INFO: error extracting
    category: "extract"
    trace: "TypeError: schema._def.shape is not a function\n    at transformUrlStringsToNumericIds (/app/node_modules/.pnpm/@browserbasehq+stagehand@2.4.2-alpha-c20adb95539fed8c56a4aa413262a9c65a8e6474_deepmerge_c9e3182dcbea2ff6d4ea36ddebc2e021/node_modules/@browserbasehq/stagehand/dist/index.js:3240:29)\n    at StagehandExtractHandler.<anonymous> (/app/node_modules/.pnpm/@browserbasehq+stagehand@2.4.2-alpha-c20adb95539fed8c56a4aa413262a9c65a8e6474_deepmerge_c9e3182dcbea2ff6d4ea36ddebc2e021/node_modules/@browserbasehq/stagehand/dist/index.js:3167:50)\n    at Generator.next (<anonymous>)\n    at fulfilled (/app/node_modules/.pnpm/@browserbasehq+stagehand@2.4.2-alpha-c20adb95539fed8c56a4aa413262a9c65a8e6474_deepmerge_c9e3182dcbea2ff6d4ea36ddebc2e021/node_modules/@browserbasehq/stagehand/dist/index.js:66:24)"
    error: "schema._def.shape is not a function"