Anthropic announced on Monday, May 18, 2026, that it has acquired Stainless, a New York-based startup whose software development kit tools have been widely used by rival AI companies including OpenAI, Google, Replicate, Runway, and Cloudflare. Financial terms were not disclosed, though The Information reported last week that the deal was valued at more than $300 million.
Founded in 2022 by former Stripe engineer Alex Rattray, Stainless built software that automates the creation and maintenance of SDKs — the code libraries developers use to interact with APIs. Its platform can take API specifications and generate production-ready SDKs across multiple programming languages, including Python, TypeScript, Kotlin, Go, and Java, and automatically updates them as APIs change.
As part of the acquisition, Anthropic will wind down all hosted Stainless products, including its SDK generator. Existing customers will retain ownership of the SDKs they have already generated and retain full rights to modify and extend them. Going forward, however, the tools will be available exclusively to Anthropic.
Anthropic stated that Stainless software has powered every official Anthropic SDK since the earliest days of its API. The company is backed by Sequoia Capital and Andreessen Horowitz.
“I started Stainless because SDKs deserve as much care as the APIs they wrap,” Rattray said 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 deal removes a shared infrastructure supplier from Anthropic’s competitors. For companies building AI agents that connect to external software, SDK tools represent a key part of that development process — and those rivals will now need to look elsewhere.
Source: TechCrunch