Anthropic takes control of key SDK infrastructure used by rivals OpenAI and Google

Stainless, a startup specializing in automatically producing software developer kits (SDKs) for AI APIs, has been acquired by Anthropic in a deal valued at over $300 million. This price more than doubles Stainless’s previous valuation of $150 million from its Series A funding round in December 2024.

SDKs serve as essential code libraries that developers integrate into their projects to interface with AI services. Companies such as OpenAI, Google, Meta, Cloudflare, and Runway have relied on Stainless’s technology to generate these SDKs across multiple programming languages including Python, TypeScript, Kotlin, Go, and Java. The startup’s SDKs see tens of millions of downloads weekly, reflecting their widespread adoption.

Founded in 2022 by former Stripe engineer Alex Rattray, Stainless had secured $35 million in funding from investors like Sequoia Capital and Andreessen Horowitz prior to this acquisition. Anthropic itself was an early user of Stainless’s SDK generation tools for its own API offerings.

Impact on Competitors and Developer Ecosystem

Following the acquisition, Anthropic intends to discontinue all hosted Stainless products, including the SDK generator platform. Existing customers retain rights to previously generated SDKs and can continue to use and modify them, but no new SDKs will be produced through Stainless’s service.

This development presents a strategic challenge for OpenAI and Google. Upon contract renewals with Stainless, these companies must decide whether to invest in rebuilding their SDK tooling internally or to adopt alternative solutions such as Speakeasy or LibLab. Until such decisions are made, Anthropic holds ownership over a critical piece of infrastructure embedded in the developer onboarding process of its two largest rivals.

Strategic Significance of the Acquisition

Anthropic’s annualized revenue reached approximately $30 billion by April 2026, surpassing OpenAI’s estimated $24 billion. This acquisition appears to extend beyond enhancing developer tools, signaling a shift in competitive dynamics toward controlling the infrastructure that facilitates developer access to AI technologies.

While Anthropic does not possess a direct mechanism to disable competitors’ SDKs, owning Stainless provides it with insight and influence during contract negotiations and renewals. For developers, the immediate experience remains unchanged, but the industry’s prior reliance on a neutral provider for SDK tooling has effectively concluded.