Anthropic buys Stainless, the SDK tool its rivals also use

@AnthropicAI announced it has acquired @StainlessAPI, a startup founded by former Stripe engineer Alex Rattray (@RattrayAlex) whose software is widely used by rival AI labs, including OpenAI and Google. Financial terms were not disclosed, though The Information reported last week that the deal valued Stainless at more than $300 million, with backing from Sequoia Capital and Andreessen Horowitz.

A Tool That Powered the Competition

The New York-based startup, founded in 2022, rose to prominence in the AI industry for automating the creation and maintenance of software development kits (SDKs), the libraries developers use to interact with APIs. Stainless generates SDKs, command-line interfaces, and Model Context Protocol (MCP) servers, converting API specifications into ready-to-use libraries across TypeScript, Python, Go, Java, Kotlin, and other programming languages.

The technology is particularly valuable to companies like Anthropic, OpenAI, Google, Replicate, Runway, and Cloudflare that are building AI agents capable of connecting to external software and completing tasks on behalf of users. Stainless has powered the generation of every official Anthropic SDK since the earliest days of its API.

Rivals Lose Access

The acquisition effectively removes a key infrastructure supplier from the hands of Anthropic's competitors. Anthropic confirmed it will wind down all hosted Stainless products, including the SDK generator. Existing Stainless customers will retain the SDKs they have already generated and have full rights to modify and extend them, but the tooling will no longer be available going forward.

The deal aims to strengthen Claude's ability to connect to external data sources and tools as Anthropic shifts its focus toward AI agents. Katelyn Lesse, Head of Platform Engineering at Anthropic, said: "We're excited to bring the Stainless team into Anthropic to advance Claude's ability to connect to data and tools."

Rattray signalled a smooth transition, saying the team had been watching what developers built on Claude over the last few years, which made the decision to join Anthropic straightforward. "The team gets to keep doing the work we love, on the platform where it matters most," he said.

Sources:
Anthropic: Anthropic Acquires Stainless (Official Announcement)
TechCrunch: Anthropic has acquired the dev tools startup used by OpenAI, Google, and Cloudflare