Anthropic acquires Stainless, the SDK platform used by OpenAI and Google, for $300 million

Anthropic has announced the acquisition of Stainless, a New York startup founded in 2022 by Alex Rattray, a former engineer on Stripe's platform team. The deal was worth more than $300 million, though Anthropic has not officially disclosed the exact terms. The move shows the growing importance of developer tooling in the ecosystem of AI companies.

What Stainless is and why it matters

Stainless specializes in automating the creation and updating of Software Development Kits (SDKs), the libraries developers use to integrate with APIs. The platform turns API specifications into production-ready SDKs in several programming languages: Python, TypeScript, Kotlin, Go and Java.

Stainless's main edge over competitors is automated updates. When an API changes, the Stainless generator syncs the changes across all supported SDKs, so developers no longer have to maintain several versions of a library by hand. That saves engineers weeks of work, especially during active development.

Why Anthropic is buying now

The strategic logic is clear: Anthropic has used Stainless SDKs since the early days of its API and relied entirely on the platform to maintain its official SDKs. With the acquisition, the company not only secures its own needs but also removes a key infrastructure supplier from the hands of direct competitors, including OpenAI, Google and Cloudflare, which also made heavy use of Stainless for their integrations.

This matters especially given the exponential growth of AI agents. Modern agents must connect reliably to thousands of different services and platforms, from payment systems to CRMs and from cloud storage to specialized tools. Each of them needs a reliable, up-to-date and well-documented SDK.

"SDKs deserve the same care as the APIs they wrap," said

Alex Rattray, expressing enthusiasm about joining Anthropic, the platform where he says his work matters most.

What will shut down and what will stay

Anthropic will end support for all hosted Stainless products, including the cloud SDK generator that previously ran as SaaS. Existing customers will not lose their SDKs, however: they remain fully owned by their users, with all rights to modify and extend the code.

• All Stainless cloud services will be shut down in the coming months
• Existing SDKs remain the property of customers, with full rights
• Developers can freely modify and maintain their own code
• Older SDKs will keep working without changes
• Customers do not need to migrate immediately

What this means for the industry

The purchase signals that developer infrastructure is becoming a strategic asset in the AI race. When OpenAI, Google and Cloudflare chose Stainless, it was a niche tool. Now Anthropic is showing that such capabilities should be held in-house, so that a company depends on no one at critical points of its development chain.

Expect other major AI companies to follow the same path and consolidate critical infrastructure inside their organizations.