Anthropic disclosed on Monday that it has acquired Stainless, a New York‑based startup that automates the creation and upkeep of software development kits (SDKs) for APIs. Founded in 2022 by Alex Rattray, a former Stripe engineer, Stainless quickly became a go‑to solution for AI labs and cloud providers that need to keep SDKs in sync with rapidly evolving APIs.

The terms of the transaction were not released, but The Information reported last week that Anthropic was in talks to buy the company for more than $300 million. Investors Sequoia Capital and Andreessen Horowitz, which backed Stainless, have not commented on the valuation.

Stainless’s platform takes an API specification and produces production‑ready SDKs in multiple languages, including Python, TypeScript, Kotlin, Go and Java. It also monitors API changes and automatically updates the generated SDKs, eliminating the manual effort that traditionally slows developers down. That capability proved especially valuable for firms building AI agents that must interact with external software, such as OpenAI, Google, Replicate, Runway and Cloudflare.

Anthropic said the acquisition will “take a key infrastructure supplier out of the hands of Anthropic’s competitors.” The company plans to wind down all hosted Stainless products, including its SDK generator, but existing customers will retain full ownership of the SDKs they have generated to date. They can modify and extend those SDKs without restriction, according to an Anthropic spokesperson.

According to Anthropic, Stainless’s software has powered the generation of every official Anthropic SDK since the earliest days of its API. “I started Stainless because SDKs deserve as much care as the APIs they wrap,” Rattray wrote in a press release. “Anthropic was one of the first teams to bet on this with us. We have been watching what developers have built on Claude over the last few years, which made bringing our teams together an easy decision.”

The move positions Anthropic to keep its own SDK pipeline under tighter control while denying rivals a tool that streamlined their development cycles. Industry observers note that the deal underscores the growing strategic importance of developer‑facing infrastructure in the AI race.

This article was written with the assistance of AI.
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