Anthropic has completed the acquisition of Stainless, a New York-based startup founded in 2022 by former Stripe engineer Alex Rattray. The deal, valued at over $300 million according to The Information, gives Anthropic ownership of a key infrastructure provider that had been serving its primary competitors, including OpenAI, Google, and Cloudflare. Anthropic did not disclose the official terms of the transaction.
Stainless built its reputation by automating the creation and maintenance of software development kits, or SDKs — the essential libraries that developers use to interact with APIs. Rattray developed a platform capable of taking API specifications and transforming them into production-ready SDKs across multiple programming languages, including Python, TypeScript, Kotlin, Go, and Java. The platform automatically updates SDKs whenever underlying APIs change, eliminating the tedious manual work of maintaining them.
The timing of this acquisition is significant for the AI industry. Companies like OpenAI, Google, Replicate, Runway, and Cloudflare rely heavily on SDK tools to build AI agents capable of connecting to external software and completing tasks on behalf of users. Anthropic confirmed it will wind down all hosted Stainless products, including its SDK generator, meaning these tools will no longer be available to competitors going forward. Existing customers will retain ownership of SDKs they have already generated and can continue to modify and extend them.
According to Anthropic, Stainless software has powered every official Anthropic SDK since the earliest days of its API. In a press release, Rattray said he started Stainless because "SDKs deserve as much care as the APIs they wrap," adding that watching what developers built on Claude made combining the teams an easy decision.