Anthropic buys Stainless for $3 billion

Anthropic said on May 18 it acquired Stainless, a New York-based developer-tools startup whose software is used to generate software development kits, command-line tools and Model Context Protocol servers for APIs. The company did not disclose the purchase price in its announcement. The deal was reported a day earlier on X with a price near $3 billion, but Anthropic’s statement gave no valuation and prior reporting from The Information said the talks were for at least $300 million. Stainless had become a shared supplier across the AI industry. Its website says customers included Anthropic, OpenAI and Cloudflare, and Anthropic said Stainless had powered every official Anthropic SDK since the earliest days of its API. TechCrunch reported that Anthropic plans to wind down hosted Stainless products, including its SDK generator, leaving the tools unavailable to rival labs going forward. ### Where did the $3 billion figure come from? An X post circulated on May 18 claiming Anthropic had bought Stainless for about $3 billion. Anthropic’s official announcement did not mention any price. The Information reported on May 13 that Anthropic was in advanced talks to acquire Stainless for at least $300 million, according to a person with knowledge of the deal. TechCrunch, citing that earlier report, said on May 18 that Anthropic did not disclose terms after confirming the acquisition. ### What exactly does Stainless make? Stainless says it turns an API specification into SDKs across languages including TypeScript, Python, Go, Java and Kotlin. (anthropic.com) Anthropic said hundreds of companies rely on Stainless to generate SDKs, CLIs and MCP servers, which are the tools developers and agents use to connect to an API. Alex Rattray, Stainless’ founder and chief executive, said in Anthropic’s release that he started the company because “SDKs deserve as much care as the APIs they wrap.” Katelyn Lesse, Anthropic’s head of platform engineering, said the companies had worked together from the start of Anthropic’s API effort. (theinformation.com) ### Which companies were using it before the deal? Stainless’ public site lists Anthropic, OpenAI and Cloudflare among customers. (anthropic.com) A 2024 Stainless blog post said its SDK generator was used for top AI model providers including OpenAI, Anthropic and Meta’s Llama models. TechCrunch reported that Stainless had also been widely used by OpenAI and Google. Anthropic’s own announcement was narrower, saying only that hundreds of companies rely on the product. (anthropic.com) ### What changes now for existing Stainless customers? Anthropic told TechCrunch that hosted Stainless products will be wound down. The company also said customers will continue to own the SDKs they have already generated and retain full rights to modify and extend them. (stainless.com) Stainless’ homepage now says “Stainless is joining Anthropic” and links to Anthropic’s acquisition announcement. (techcrunch.com) Anthropic said the combined teams will focus on developer experience and agent connectivity on the Claude platform. ### How does this fit into Anthropic’s broader expansion? Anthropic raised $30 billion in Series G funding in February at a $380 billion post-money valuation, according to the company. The company said that capital would support research, product development and infrastructure expansion. (techcrunch.com) May 18 is now the operative date for the next step in this deal, because Anthropic has already posted the acquisition announcement and Stainless has updated its website to reflect the combination. (stainless.com) Anthropic said the Stainless team will join its effort to build SDKs and MCP tooling for the Claude platform. (anthropic.com 1) (anthropic.com 2)