Anthropic on Monday announced its acquisition of Stainless, the New York startup whose SDK automation tools quietly underpin developer libraries at OpenAI, Google, and Cloudflare. Terms were not disclosed in the official announcement. The Information had reported last week the deal was worth more than $300 million.
Founded in 2022 by former Stripe engineer Alex Rattray, Stainless turns API specifications into production SDKs across Python, TypeScript, Go, Java, and Kotlin. Anthropic says the company has powered every official Claude SDK since the earliest days of its API. More recently, Stainless expanded into Model Context Protocol server tooling, the connectors that let AI agents call external APIs.
That MCP angle is the point. Anthropic authored the protocol, and now owns the most prominent toolchain for generating servers that implement it. "Agents are only as useful as what they can connect to," said Katelyn Lesse, head of platform engineering at Anthropic, in the announcement. That's the corporate framing. The practical effect is harder to dress up.
Anthropic told TechCrunch it will wind down all hosted Stainless products, including the flagship SDK generator. Existing customers keep ownership of SDKs already generated and can modify them. New signups are closed. OpenAI, which previously abandoned its own in-house SDK effort and migrated to Stainless because maintenance was too costly, now finds its developer libraries maintained by a subsidiary of its direct competitor.
The deal is Anthropic's fourth acquisition in roughly six months, after computer-use startup Vercept and biotech firm Coefficient Bio. The Stainless team joins Anthropic. Rivals can shift to alternatives like Speakeasy or the open-source OpenAPI Generator, but rebuilding a multi-language SDK pipeline is exactly the work OpenAI walked away from.
Bottom Line
Anthropic now owns the SDK generator that OpenAI, Google, and Cloudflare have been using to ship developer libraries.
Quick Facts
- Acquisition price reportedly over $300 million per The Information; terms officially undisclosed
- Stainless founded in 2022 by former Stripe engineer Alex Rattray
- Backed by Sequoia Capital and Andreessen Horowitz
- Generates SDKs in Python, TypeScript, Go, Java, Kotlin
- Anthropic's fourth acquisition in roughly six months
