Anthropic acquires Stainless, a developer of official SDK and MCP server tools.



Anthropic, the AI company that develops Claude, has announced that it has acquired Stainless, the developer of the official SDK (Software Development Kit) and MCP server tools. The terms of the acquisition, such as the price, have not been disclosed.

Anthropic acquires Stainless \ Anthropic
https://www.anthropic.com/news/anthropic-acquires-stainless

Stainless - Blog - Stainless is joining Anthropic
https://www.stainless.com/blog/stainless-is-joining-anthropic/

Anthropic has acquired the dev tools startup used by OpenAI, Google, and Cloudflare | TechCrunch
https://techcrunch.com/2026/05/18/anthropic-has-acquired-the-dev-tools-startup-used-by-openai-google-and-cloudflare/

Stainless, founded in 2022, has supported the development and maintenance of all official SDKs for the Anthropic API since its early days. Stainless translates API specifications into SDKs for various languages, including TypeScript, Python, Go, Java, and Kotlin. Each SDK is designed to be fast, reliable, and natively usable in its respective language.



Furthermore, Stainless's software is used by competing AI companies such as OpenAI and Google, and is highly valued by companies developing AI agents that can connect to external software and perform tasks on behalf of users.

Following this acquisition, Stainless states that it will phase out its hosted Stainless products, including its SDK generator. New registrations, projects, and SDKs will no longer be available. This means that, going forward, only Anthropic will be able to use Stainless's SDK tools, while competitors will no longer be able to.

However, Stainless states that 'Stainless customers will continue to own the SDKs generated by the SDK generator and will retain full rights to freely modify and extend them.'

While the exact acquisition price has not been disclosed, the overseas media outlet The Information reports that it is over $300 million (approximately 47.5 billion yen).



Caitlin Lesse, Head of Platform Engineering at Anthropic, said, 'Stainless has shaped how developers experience the Claude API from the very beginning. It has been a fantastic experience working with them. The usefulness of an agent depends on what it can connect to. We are excited to welcome the Stainless team to Anthropic to further enhance Claude's ability to connect to data and tools.'

Alex Rattray, founder and CEO of Stainless, commented, 'We founded Stainless because we believe that an SDK should be treated with the same care as the APIs it wraps. Anthropic was one of the first teams to share this idea with us. We've been watching what developers have been building on Claude for the past few years, so merging the two teams was an easy decision. The teams can continue doing the work we love on the platform that matters most to them.'

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