Anthropic acquires Stainless to expand Claude's SDK and tool reach
Anthropic bought Stainless to own more of the tooling layer around Claude. The New York startup has powered every official Anthropic SDK since the API’s earliest days.
Anthropic’s acquisition of Stainless is a move to control more than the model itself. By bringing in the New York startup that generates developer tooling, Anthropic is reaching deeper into the stack that determines how builders connect AI systems to data, APIs, and external software, a layer that is becoming central as agents take on more action-oriented tasks.
Anthropic announced the deal on May 18, 2026 and said Stainless will wind down all hosted products as part of the acquisition. The company framed the purchase as part of the shift from models that answer questions to agents that act on them. Anthropic also tied the deal to MCP, the connectivity standard it created to make agent integrations possible, underscoring how much of the competition in AI is now moving from raw model performance to the plumbing around it.
Stainless was founded in 2022 by Alex Rattray, a former Stripe engineer, and has built a business around turning API specifications into SDKs across TypeScript, Python, Go, Java, Kotlin, and other languages. Stainless also offers documentation tools, a CLI, a Terraform provider, and MCP servers. Anthropic said Stainless has powered every official Anthropic SDK since the earliest days of Anthropic’s API, making the acquisition as much a consolidation of existing dependencies as a new strategic bet.
The startup says it is trusted by OpenAI, Anthropic, Cloudflare, Google and others, and it lists more than 1,000 live SDKs and more than 110 million packages downloaded each week. Its company page says the team is focused on giving APIs a Stripe-quality developer experience, a pitch that has helped attract industry figures including Daniel Schafer, Guillermo Rauch, Søren Bramer Schmidt, Calvin French-Owen, and Cristina Cordova as backers or advisors, alongside Sequoia.
Anthropic did not disclose deal terms. Before the announcement, the companies were said to be in advanced talks over a purchase valued at least $300 million. The Stainless deal follows a pattern for Anthropic, which has been adding specialist teams and then folding their outside products inward, as it did with Vercept, another recent acquisition that said it would wind down its external product after joining Anthropic.
The timing also fits Anthropic’s wider infrastructure push. In recent weeks, the company announced a $200 million partnership with the Gates Foundation, a compute deal with SpaceX, and a partnership with Google and Broadcom that Anthropic said expands its U.S.-based compute footprint. The message is clear: in the AI arms race, owning the pipes developers use may matter almost as much as building the models themselves.
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