Anthropic has acquired Stainless, a startup that uses AI to automatically package complex APIs into cross-language SDKs. After the deal closes, the entire Stainless team will join Anthropic to help Claude connect with external tools and data.
The acquisition effectively gives Anthropic control over a key piece of its competitors’ infrastructure. OpenAI had previously abandoned in-house SDK development in favor of relying entirely on Stainless, finding it too resource-intensive to maintain multi-language SDKs internally. While alternatives like Speakeasy and LibLab exist, all three of the top LLM vendors — OpenAI, Google, and Anthropic — currently use Stainless to generate SDKs.
The exact price wasn't disclosed, but The Information previously reported the deal is worth at least $300 million — double Stainless’s $150 million valuation from last December.
Beyond serving the big three, Stainless had also built companion tools for Anthropic’s Model Context Protocol (MCP). This marks Anthropic’s fourth acquisition in six months: after buying JavaScript runtime Bun last year, it went on to snap up computer operation startup Vercept and AI biotech firm Coefficient Bio.