Anthropic Acquires Stainless and Will Wind Down Hosted SDK Services

Anthropic on May 18, 2026 announced the acquisition of Stainless, a New York startup that automates the creation and upkeep of software development kits (SDKs). As part of the deal, Anthropic said it will wind down all hosted Stainless products, explicitly including Stainless’s hosted SDK generator. The move centralizes a popular SDK automation capability inside Anthropic and removes a widely used hosted supplier from the broader market.

The company did not disclose financial terms of the acquisition. Media reporting last week said Anthropic had been in talks to acquire Stainless for more than $300 million. Anthropic also said that existing Stainless customers will retain ownership of any SDKs they’ve generated to date and will have full rights to modify and extend those SDKs. Stainless was founded in 2022 by former Stripe engineer Alex Rattray. The startup built tooling that converts API specifications into production‑ready client libraries across languages such as Python, TypeScript, Kotlin, Go and Java, and it automatically updates those SDKs when APIs change. That automation replaces manual, error‑prone work for platform teams and client‑library maintainers.

The technology had become common infrastructure among AI builders: reports indicate Stainless was used by OpenAI, Google, Replicate, Runway and Cloudflare, among others. Anthropic said Stainless software has powered every official Anthropic SDK since the earliest days of its API, signaling a long-standing technical dependency that the company has now internalized. For developers and platform teams that relied on Stainless’s hosted service, the acquisition means they will need to find or build alternative hosted tooling if they want the same automation going forward, although their already generated SDKs remain theirs to use and adapt. Anthropic’s choice to bring the tooling in‑house reduces the independent options available to competing AI companies and developer platforms.

Alex Rattray commented that Anthropic’s existing use of Stainless and developer activity on the company’s Claude models made the teams’ integration an “easy decision,” and he said the Stainless team will continue working on the platform under Anthropic. With the hosted product winding down, the immediate next steps for enterprises and independent developers will be to evaluate retention of current SDKs, migration strategies, or self‑hosted alternatives.