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Stagehand 4.1 does not work with Apostate 0.4.3. Stagehand.create() stops with Stagehand initialization timed out after 60000ms, whether it launches Apostate (localBrowser.launch with executablePath) or connects to it over CDP (localBrowser.connect with --remote-allow-origins=* on the browser). The same scripts start on Chrome for Testing. Measured on 2026-09-28 on macOS arm64. Stagehand 4 drives the browser from its own browser extension, which it loads over CDP and which opens a second DevTools connection from inside the browser. That path does not complete under Apostate. It is tracked as a known issue. Until it is fixed, use one of these for model-driven browsing:

MCP server

Browser tools for any MCP client, on an Apostate browser launched by the Node package.

browser-use

A Python agent framework, connected to Apostate over CDP.

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What a page sees under Stagehand 4

Measured on Chrome for Testing, where Stagehand 4 does start:
  • window.ModelContext exists and navigator.modelContext is an object. Stagehand enables Chromium’s WebMCP feature for its own use, and pages can read it. Desktop Chrome does not expose it.
  • Stagehand’s default trace endpoint is https://example.com/v1/traces, and the extension exports traces from inside the browser. Set telemetry: { traces: { endpoint: ... } } to your own collector.
  • The model API key is handed to the extension, and model calls go out through the browser’s network stack and proxy.