Anthropic acquires Stainless for $300M+ to lock down SDK tools
The dev tool behind every major AI API is now exclusive to Claude.
Anthropic announced the acquisition of Stainless, the developer tools startup that has been responsible for building and maintaining the official SDKs (software development kits) for the Claude API since its early days. The deal, reported to be over $300 million, gives Anthropic exclusive control over Stainless's SDK generator and MCP server tools—technology that was previously used by competitors including OpenAI, Google, and Cloudflare. Stainless translates API specs into fast, native SDKs for TypeScript, Python, Go, Java, and Kotlin, making it a critical piece of infrastructure for AI developers.
Following the acquisition, Stainless will wind down its hosted products, meaning new registrations, projects, and SDK generation will no longer be available to external customers. However, existing customers retain full ownership and modification rights to SDKs already generated. Anthropic head of platform engineering Caitlin Lesse emphasized that the move will deepen Claude's ability to connect to external tools and data, a key requirement for building effective AI agents. Stainless founder Alex Rattray noted the teams have shared a vision for SDK quality from the start, and merging will accelerate work on the platform that matters most to them.
- Acquisition price reportedly over $300M (approx. 47.5 billion yen); terms not officially disclosed.
- Stainless built SDKs for Anthropic, OpenAI, Google, and Cloudflare; hosted products now exclusive to Anthropic.
- Existing customers retain full rights to previously generated SDKs; new SDK generation ceases for external users.
Why It Matters
Anthropic locks down a key developer dependency, limiting competitors' SDK quality while bolstering Claude's agent ecosystem.