Anthropic in talks to buy Stainless

Anthropic was in advanced talks this week to acquire Stainless, a startup that builds software development kits and related tooling for API companies, according to The Information and DigiTimes. The reports, published on May 13 and May 14, said the deal could value Stainless at more than $300 million. Anthropic and Stainless had not publicly announced a transaction as of Thursday, May 14. Stainless says its software is used by companies including OpenAI, Google, Cloudflare and Anthropic itself. ### Why would Anthropic want a company that makes SDKs? Stainless sells the developer-facing layer that turns an API specification into official client libraries, documentation, command-line tools and, more recently, MCP servers. On its documentation site, Stainless says customers can generate SDKs, docs, a CLI, an MCP server and other tooling from an OpenAPI specification. Its marketing materials describe the product as a way to deliver “idiomatic and polished SDKs” without maintaining each language client by hand. (theinformation.com) The company’s own customer materials name OpenAI and Anthropic among users of those tools. In a blog post announcing its SDK generator, Stainless said it generated official client libraries for OpenAI, Anthropic and Cloudflare. On its customer pages, Stainless says OpenAI used the company’s tooling to improve its developer libraries, while the main site lists Google among the companies that trust the platform. (stainless.com) ### What exactly does Stainless make for model companies? OpenAPI specifications are the core input for Stainless’s products, according to the company’s documentation. From that spec, Stainless says it can produce language-specific SDKs, API reference documentation, a command-line interface, Terraform providers and MCP servers. That places the company in the workflow between a model provider’s backend API and the software that outside developers actually install and use. (stainless.com) Alex Rattray, Stainless’s founder and chief executive, described the pitch in a 2024 company blog post as replacing repetitive maintenance work across multiple programming languages. Stainless said at the time that its tools handled requests, retries, streaming and pagination in generated clients. Those details matter because model providers now compete not only on model performance and price, but also on how quickly developers can adopt new features through official libraries. (stainless.com) ### How large is the reported deal? The Information reported on May 13 that Anthropic was in advanced talks to buy Stainless for at least $300 million, citing a person with knowledge of the matter. DigiTimes, in a separate report published May 14, said the potential transaction was valued at more than $300 million. Neither report said a definitive agreement had been signed. (stainless.com) Anthropic has recently shown a willingness to use acquisitions and partnerships as it expands its enterprise business. In March, the company said it had acquired Vercept to advance Claude’s computer-use capabilities. On May 4, Anthropic also announced a new enterprise AI services company with Blackstone, Hellman & Friedman and Goldman Sachs. ### Why does Stainless matter beyond one startup sale? (theinformation.com) Stainless’s customer list puts it in business with several of the largest API providers in artificial intelligence. The company says it is trusted by OpenAI, Anthropic, Cloudflare and Google, and its OpenAI case study describes work on official SDKs used by developers building on OpenAI’s platform. That makes Stainless part of the infrastructure through which model companies package and distribute their APIs to customers. (anthropic.com) The reported talks also come as Anthropic is spending heavily to expand its commercial footprint. On Feb. 12, Anthropic said it had raised $30 billion in Series G funding at a $380 billion post-money valuation, with the proceeds earmarked for research, product development and infrastructure. A Stainless acquisition at the reported price would be small relative to that financing, but it would add a developer-tools asset tied directly to API distribution. (stainless.com) ### What should readers watch next? May 14 is the key date so far because neither Anthropic’s newsroom nor Stainless’s public site showed a deal announcement by Thursday. The next concrete milestone would be a statement from Anthropic, Stainless or investors confirming a signed agreement, a price or closing terms. (anthropic.com 1) (anthropic.com 2)