Anthropic acquires dev tool firm Stainless for $300m

Anthropic said on May 18 that it has acquired Stainless, a New York-based startup founded in 2022 by former Stripe engineer Alex Rattray that builds tools for generating and updating software development kits.

The company did not disclose the financial terms of the transaction. However, according to the reports, last week, the company was in talks to purchase the startup, which is backed by Sequoia Capital and Andreessen Horowitz, for more than US$300m.

Anthropic said it will wind down hosted Stainless products, including its SDK generator, while existing customers will keep the SDKs they have already generated and retain rights to modify and extend them.

🔗 Source: Anthropic

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Anthropic bought infrastructure many AI developers use

Stainless was more than a small vendor. It made software development kits, or SDKs, that let developers reach models from Anthropic rivals such as OpenAI, Google and Meta.
The deal was Anthropic’s first. Its reported price was at least US$300 million, far above Stainless’ December 2024 US$25 million series A raise, a funding round for startups past the earliest stage.
Founder Alex Rattray built SDK tooling at Stripe. Stainless said that work shaped its system for producing higher-quality SDKs than open-source options, which is software the public can use and modify.

The deal leaves OpenAI, Google and others with a dependency problem

Anthropic plans to wind down Stainless’ hosted products, including its SDK generator. Rival model providers now face a choice. They can keep using tools owned by a competitor or rush to build or buy another option.
The purchase fits a wider push by AI labs to own developer infrastructure. Examples include OpenAI’s reported acquisition of Astral, known for Python developer tools. Another is Anthropic’s reported December 2025 purchase of Bun, a JavaScript runtime, which is software for running JavaScript applications.
That wind-down may open room for Liblab and Speakeasy. Both make tools that automatically create software libraries. Some Stainless customers now need a new provider for hosted SDK generation and related services.