Anthropic acquires SDK startup Stainless used by OpenAI and Google

Anthropic announced on Monday that it has bought Stainless, the New York startup whose SDK automation platform is used by OpenAI, Google and Cloudflare [1]. The deal, reported to be over $300 million, brings the entire Stainless team and its code‑generation technology in‑house and will see all hosted Stainless products, including its SDK generator, wound down [1].

Stainless was founded in 2022 by former Stripe engineer Alex Rattray to turn API specifications into production‑ready SDKs across languages such as Python, TypeScript, Kotlin, Go and Java [1]. Its platform automatically updates SDKs as APIs evolve, eliminating the manual maintenance that traditionally slows developer adoption. By automating this “unglamorous” infrastructure, Stainless became a critical layer for AI labs building agents that need to call external software, a use case that Anthropic, OpenAI, Google, Replicate, Runway and Cloudflare all rely on [1].

Anthropic says the acquisition removes a key infrastructure supplier from its competitors’ hands. Existing Stainless customers will retain the SDKs they have already generated and can modify them freely, but no new hosted SDKs will be offered after the wind‑down [1]. The company’s spokesperson noted that every official Anthropic SDK to date has been powered by Stainless software, underscoring the strategic fit [1]. Rattray, in a press release, highlighted that Anthropic was one of the first teams to back Stainless and that the move lets his team continue work on the platform where it matters most [1].

The purchase signals Anthropic’s broader push to own more of the developer experience. While rivals such as OpenAI and Google have expanded their own SDK and API ecosystems, Anthropic has lagged in tooling that keeps developers locked into its platform. By internalizing Stainless’s automated SDK generation, Anthropic can streamline its own Claude‑based services and reduce reliance on third‑party tooling, potentially accelerating product rollout and improving developer retention.

What remains to watch is how quickly Anthropic can integrate Stainless’s technology into its own stack and whether competitors will respond with comparable in‑house solutions. The shutdown of hosted products leaves existing users scrambling for alternatives, and the move could set a precedent for AI labs to acquire critical developer‑infrastructure assets rather than build them from scratch.