Acquire OpenAI's SDK Foundry Directly! Anthropic Acquires Stainless with a Double Premium

According to Dynamic Beating Monitor, Anthropic has announced the official acquisition of the developer tool startup Stainless. This company specializes in using AI to automatically package complex APIs into cross-language SDKs. After the transaction is completed, the Stainless team will be fully integrated into Anthropic, specifically to help Claude bridge external tools and data.

This transaction effectively puts Anthropic in direct control of a competitor's underlying toolchain. Due to the high engineering cost of maintaining a multi-language SDK internally, OpenAI had previously abandoned internal development altogether and fully embraced Stainless. Although there are alternative solutions on the market such as Speakeasy and LibLab, the top three large model vendors (OpenAI, Google, Anthropic) are all currently using Stainless to generate SDKs.

The official transaction amount has not been publicly disclosed. However, according to The Information's previous report, the acquisition price is at least $300 million, doubling directly from Stainless's $150 million valuation in December last year.

In addition to serving the top three model vendors, Stainless had previously developed complementary tools for Anthropic's MCP (Model Context Protocol) that was released. This is Anthropic's fourth acquisition in six months: following the acquisition of the JavaScript runtime Bun last year, it has subsequently swallowed up the computer operation vendor Vercept and the AI biotech company Coefficient Bio.