Anthropic acquires SDK generator Stainless, whose tools power OpenAI and Google client libraries

Stainless turns an API spec into SDKs, command-line tools and MCP servers in languages including TypeScript, Python, Go, Java and Kotlin. Hundreds of companies used it. OpenAI's official client libraries were generated with Stainless, and Google was also a customer. Anthropic did not disclose a price; the deal was reportedly worth more than $300M. Stainless planned to shut its hosted platform on Sept. 1, 2026, which leaves customers to maintain their own SDKs. The purchase came after Anthropic bought Bun in December, Vercept two months later and Coefficient Bio in April. Together they extend its control over the tooling around Claude. OpenAI made a similar move when it agreed to buy Astral in March. For developer tool founders, this is both a warning and an opportunity. A product every lab depends on is especially valuable to one lab. After a sale it can be shut down for everyone else, so customers should plan for that concentration risk.