# Stagehand Browser Agent SDK (@browserbasehq/stagehand) - AgentBreakWatch Reference

> TL;DR Verdict: Stagehand Browser Agent SDK (`@browserbasehq/stagehand`) is currently at v4.3.0 on NPM (published 2026-10-20), with a 90-day Stability Score of 78/100 (B) and HIGH schema drift risk across 10 releases in the last 90 days. v4.x overhauls stagehand.act() and stagehand.extract() options object, separating modelClient configuration from Playwright page lifecycle.

## Live Telemetry Metadata
- Canonical Page: https://agentbreakwatch.vercel.app/p/stagehand
- Category Hub: https://agentbreakwatch.vercel.app/c/agent-sdks (AI Agent SDKs & Frameworks Breaking-Change Index)
- Package Name: `@browserbasehq/stagehand`
- Registry: NPM (https://www.npmjs.com/package/@browserbasehq/stagehand)
- GitHub Repository: https://github.com/browserbase/stagehand
- Vendor: Browserbase
- Latest Live Version: v4.3.0
- Published Date: 2026-10-20T00:40:20.973Z
- 90-Day Release Count: 10
- Direct Dependencies: 4
- License: MIT
- Stability Score: 78/100 (Grade B)
- Schema Drift Risk: HIGH
- Recommended Exact Pin Command: `npm install @browserbasehq/stagehand@4.3.0`
- Watched Symbols / MCP Tools: Stagehand, page.act, page.extract, page.observe
- Snapshot Timestamp: 2026-10-24T12:11:27.697Z

## Breaking Change & Schema Drift Summary
v4.x overhauls stagehand.act() and stagehand.extract() options object, separating modelClient configuration from Playwright page lifecycle.

## Migration Diff: Before (Deprecated / Unpinned Pattern)
```
await stagehand.page.act({ action: "click sign in", modelName: "gpt-4o" });
```

## Migration Diff: After (Verified v4.3.0 Pattern)
```
await stagehand.act("click sign in");
```

## Recent Verified Releases
- v4.3.0 (published 2026-10-20) [LATEST]
- v4.2.1 (published 2026-10-11)
- v4.2.0 (published 2026-10-08)
- v4.1.0 (published 2026-09-09)
- v4.0.3 (published 2026-09-09)
- v3.7.3 (published 2026-08-28)