Anthropic in talks to buy Stainless $300M

Anthropic is in advanced talks to acquire developer-tools startup Stainless for at least $300 million, The Information reported on May 13, citing a person with knowledge of the discussions. Stainless sells software that turns APIs into software development kits, or SDKs, used by developers to connect applications to AI models and other services. The talks have not produced a final agreement, and terms could still change, according to the report. Anthropic and Stainless did not announce a transaction on their official news pages or websites as of May 14. ### What does Stainless actually sell? Stainless says it provides tools for generating SDKs, documentation and MCP servers from an API, with the goal of giving software companies a more polished developer interface. On its website, the company says customers and partners include Anthropic, Cloudflare, Google and OpenAI. Alex Rattray, Stainless’s founder and chief executive, wrote in a Series A post that the company raised $25 million in funding led by Andreessen Horowitz, with participation from Sequoia and The General Partnership. (theinformation.com) In an earlier product announcement, Stainless said it generated official client libraries for OpenAI, Anthropic and Cloudflare. (stainless.com) TechCrunch reported in April 2024 that OpenAI, Anthropic and Together AI were using Stainless to generate SDKs for their APIs. A later TechCrunch profile said the company’s software compiles API specifications into SDKs in languages including Python, TypeScript, Kotlin and Go. (stainless.com) ### Why would Anthropic want this company? The reported target sits close to Anthropic’s developer business. Anthropic’s website lists a Claude Platform, developer docs, pricing and marketplace offerings, alongside products such as Claude Code and Claude Code for Enterprise. Stainless’s software is used to package APIs into the tools developers actually install and call from code. (techcrunch.com) If Anthropic were to buy Stainless, it would add ownership of a layer that sits between model providers and outside developers, based on Stainless’s product descriptions and customer list. That is an inference from the companies’ published materials and the reported talks, not a stated rationale from Anthropic. (anthropic.com) ### How large would the deal be for Anthropic? The reported purchase price is at least $300 million. The Information said part of the consideration could be paid in Anthropic shares, according to follow-on reports that attributed details to the same story. Anthropic said on February 12 that it raised $30 billion in Series G funding at a $380 billion post-money valuation. (stainless.com) That announcement followed a $13 billion Series F round at a $183 billion post-money valuation on September 2, 2025, according to the company. Those financing figures show Anthropic has recently had access to capital on a scale that would make a $300 million acquisition relatively small by comparison. (theinformation.com) That comparison is based on Anthropic’s disclosed fundraising amounts and the reported Stainless price. ### Has either company confirmed the talks? (anthropic.com) Anthropic’s newsroom on May 14 showed recent announcements on products, partnerships and regional expansion, but no acquisition statement about Stainless. Stainless’s announcements page and company pages likewise did not show a posted deal announcement. The Information’s report remains the central published account of the talks. (anthropic.com) Reuters-style pickup reports carried by MSN and other outlets said Anthropic was in talks to buy Stainless for more than $300 million and that the deal had not been finalized. ### What should readers watch next? (anthropic.com) A signed merger agreement, a regulatory filing or an official post from Anthropic or Stainless would be the next concrete milestone. Until then, the public record consists of the May 13 report about advanced talks, Stainless’s published customer list and product materials, and Anthropic’s existing platform and funding disclosures. (theinformation.com)