Anthropic bought Stainless, the SDK factory OpenAI and Meta also ran on

Anthropic has acquired Stainless and plans to shut the hosted service down. The startup auto-generates SDKs from API specs, and its customer list reads like a who’s who of Anthropic’s rivals: OpenAI, Meta, Google, and Cloudflare all ran on it.

That last part is what makes a routine acquihire interesting. Stainless quietly sat in the supply chain of half the frontier AI labs, and the company that just bought it competes with most of them. Anthropic announced the deal on May 18, and the news got fresh attention after Gergely Orosz, who writes The Pragmatic Engineer, flagged the competitor-dependency angle to his audience.

What we know

The confirmed facts come straight from both sides, so there’s little to hedge here. Anthropic announced the deal on May 18, The Information put the price above $300 million, and the company says the hosted generator is shutting down. Why it matters: a tool quietly wired into OpenAI, Meta, and Google’s release pipelines just changed hands to a lab that competes with all three. The rest is detail.

• Anthropic acquired Stainless, the New York startup founded in 2022 by former Stripe engineer Alex Rattray, Anthropic confirmed on May 18. The Information reported the deal valued the company at more than $300 million, roughly double its December 2025 valuation.
• Stainless turns an API specification into a finished SDK, plus command-line tools and an MCP server, across TypeScript, Python, Go, Java, Kotlin, and more. Hand it your OpenAPI spec, get back client libraries developers can install today.
• The customer roster includes Anthropic’s direct competitors. Per TechCrunch, OpenAI, Google, Meta, Cloudflare, Runway, and Replicate all used the platform. It also generated every official Anthropic SDK from the API’s earliest days.
• The hosted products are going away. Anthropic said it will “wind down all hosted Stainless products, including its SDK generator.” New signups and projects are off the table.
• Customers keep what they’ve already built. An Anthropic spokesperson told TechCrunch that “Stainless customers will still own the SDKs they’ve generated to date and have full rights to modify and extend them however they wish.”

What we don’t know

The shape of the wind-down is the open question. Anthropic hasn’t published a firm shutdown date, a migration path, or a tool to export a project’s generation config so a team could re-run it elsewhere. Owning the output isn’t the same as owning the machine that produced it: without the hosted generator, every future API change means hand-maintaining libraries Stainless used to regenerate on demand.

It’s also unclear what happens to the rivals mid-flight. OpenAI and Google have the engineering depth to rebuild this in-house. Smaller shops on the platform don’t. Nobody has said how long they have.

Who reported it

The acquisition itself is on the record: Anthropic’s own announcement, TechCrunch, and The New Stack all covered it the week of May 18. Orosz amplified the part the press releases soft-pedaled, that a vendor embedded in competitors’ stacks just got pulled off the board.

Anthropic framed the buy around agents, not rivalry. “Agents are only as useful as what they can connect to,” said Katelyn Lesse, the company’s head of platform engineering. Rattray, for his part, said: “I started Stainless because SDKs deserve as much care as the APIs they wrap. Anthropic was one of the first teams to bet on this with us.”

What this means for you

If you build on a small, sharp vendor, this is the risk in one news cycle. Stainless wasn’t a flaky startup that ran out of money. It was good enough that a frontier lab paid nine figures to absorb it, and “good enough to acquire” and “still here next quarter” turned out to be different things. The lesson isn’t to avoid promising tools. It’s to know your exit before you need it. Ask any vendor in your critical path: if you vanished tomorrow, can I export everything and run it myself? Stainless customers can at least keep their generated code, which is more than a lot of shutdowns offer. But the live service that kept those libraries current is gone, and the AI labs now buying up their own tooling supply chain won’t all be that generous. Treat single-vendor dependencies as something to insure against, not just integrate with.