Anthropic Anthropic Buys Stainless, the SDK Tool That Powers OpenAI and Google
Anthropic acquired Stainless, the startup behind nearly every official Claude SDK and MCP server generator, in a deal valued at over $300 million. Hosted products are being shut down, leaving competitors like OpenAI and Google to find alternatives.
Anthropic announced on May 18 that it has acquired Stainless, the four-year-old startup that automates the generation and maintenance of software development kits across Python, TypeScript, Go, Java, Kotlin, and more. The deal was valued at over $300 million according to The Information, roughly double Stainless’s $150 million Series A valuation from December 2024.
The acquisition pulls in a team that has quietly powered much of the AI ecosystem’s developer tooling. Stainless has built every official Anthropic SDK since the earliest days of the Claude API, and hundreds of other companies have relied on the platform to keep their own SDKs current as APIs evolve.
What Stainless actually does
The core product takes an API specification and generates production-ready SDKs across multiple languages, then automatically updates them whenever the API changes. That’s a problem that sounds simple but isn’t. Keeping six language clients in sync with a rapidly changing API is tedious work, and Stainless turned it into something close to a solved problem for paying customers.
More recently, the company expanded into MCP server generation. Stainless can turn a REST API spec into a Model Context Protocol server, which is directly relevant to Anthropic’s push to make Claude agents connectable to external tools and data.
Stainless founder Alex Rattray, a former Stripe engineer, framed the deal simply: “SDKs deserve as much care as the APIs they wrap. Anthropic was one of the first teams to bet on this with us.”
What changes for customers
Anthropic is winding down all hosted Stainless products. Existing customers keep full ownership and rights to any SDKs they’ve already generated and can modify or extend them without restriction. But they lose access to the platform going forward.
That creates an immediate gap for OpenAI, Google, Cloudflare, Runway, Replicate, and others that had been using Stainless to keep their SDKs maintained. The SDKs those companies already have will keep working, but automatic updates when APIs change are gone. Those teams now have to either build in-house tooling, migrate to alternatives like Speakeasy, Fern, or the open-source OpenAPI Generator, or handle SDK maintenance manually.
Anthropic’s announcement framed the acquisition as part of its agent connectivity work: “Agents are only as useful as what they can connect to.” Katelyn Lesse, Anthropic’s head of platform engineering, said the goal is bringing the Stainless team in to advance Claude’s ability to integrate with external tools and data.
The strategic angle
This is a notable move beyond the usual talent acquisition. Stainless had become shared infrastructure for competing AI labs. OpenAI’s and Google’s official client libraries were both generated through it. By acquiring Stainless and shutting down its hosted products, Anthropic has removed a piece of infrastructure its competitors depended on.
Whether the gap matters in practice depends on how quickly those teams can build alternatives. SDK generation tooling has alternatives, and OpenAI in particular has enough engineering resources to handle the transition. But for smaller companies that had been relying on Stainless to stay current, the shutdown represents real work to replace.
The Stainless team is joining Anthropic’s platform engineering organization and will focus on connecting Claude with tools, APIs, and enterprise data sources. Given the speed at which MCP adoption has grown since Anthropic open-sourced the protocol, getting the team that built the MCP generation tooling in-house makes sense.
Source: Anthropic announcement · TechCrunch