Anthropic buys the SDK startup that OpenAI and Google depend on

Anthropic has acquired Stainless, the startup that automatically generates production-ready software developer kits (SDKs) for AI APIs — including the ones OpenAI and Google ship to developers. The deal is valued at over $300 million, per The Information, more than double Stainless's $150 million Series A valuation from December 2024. The catch: Anthropic now owns the SDK layer its fiercest competitors rely on to reach developers.

What Stainless does

SDKs are the ready-made code packages developers drop into their projects to connect to an AI service — think `pip install openai` or `npm install @google/generative-ai`. Building and maintaining them in-house is expensive, which is why OpenAI, Google, Meta, Cloudflare, and Runway all outsourced the job to Stainless. The startup, founded in 2022 by former Stripe engineer Alex Rattray, automatically generates these packages from an API specification across Python, TypeScript, Kotlin, Go, and Java. Its SDKs are downloaded tens of millions of times a week.

Anthropic itself used Stainless from the earliest days of its own API. Stainless had raised $35 million total, backed by Sequoia Capital and Andreessen Horowitz, before this acquisition.

The conflict

TechCrunch confirms that Anthropic plans to wind down all hosted Stainless products, including the SDK generator itself. Existing customers keep the rights to SDKs already generated and can continue modifying and integrating them — but new generation will stop.

That creates an immediate problem for OpenAI and Google. When their Stainless contracts come up for renewal, they face a choice: rebuild SDK tooling in-house at significant cost, or switch to an alternative like Speakeasy or LibLab. Until then, Anthropic technically owns a component embedded in the developer onboarding flow of its two largest rivals.

What it signals

Anthropic's annualized revenue hit roughly $30 billion as of April 2026, ahead of OpenAI's estimated $24 billion. This acquisition looks less like a developer-tools play and more like a structural move — shifting competition from AI model quality toward control of the infrastructure developers use to access AI at all. Owning Stainless doesn't give Anthropic a direct kill switch over rivals' SDKs, but it does give it visibility and leverage at every contract renewal.

For developers, nothing changes immediately. But the industry's quiet dependence on a single neutral tooling provider has now ended.