That's the move. Anthropic announced Monday it has acquired Stainless, the startup that generates production-ready SDKs from API specifications. Terms were not disclosed, but The Information reported before the announcement that talks valued Stainless at over $300 million, with part of the consideration potentially in Anthropic equity.
Stainless, founded by former Stripe engineer Alex Rattray and backed by Sequoia Capital and Andreessen Horowitz, sits in a peculiar position in the AI toolchain: it generated every official Anthropic SDK since the API's earliest days, but it also generates the Python, TypeScript, Go, Java, Kotlin, and Ruby libraries that OpenAI, Google, Cloudflare, and Meta ship to their own developers. One startup builds the scaffolding for all of them.
Anthropic will wind down all hosted Stainless products, including the SDK generator. Existing customers retain the SDKs they have already built, with full rights to modify. The factory closes; the parts stay where they landed.
Stainless (founded 2022, backed by Sequoia and a16z) generates SDKs, CLIs, and MCP servers from API specifications. Customers include OpenAI, Google, Cloudflare, and Meta. Stainless generated every official Anthropic SDK to date. Post-acquisition: all hosted Stainless products, including the SDK generator, wind down. Existing customers retain generated SDKs with full modification rights.
Reported deal size: over $300 million per The Information. Anthropic did not disclose terms.
Resume support for background sessions. Elapsed-duration notifications when agents complete. Model selection now scoped to individual sessions rather than global. Fixes: startup hangs when the API is unreachable, terminal display corruption, macOS background session crashes in protected folders.
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