Anthropic announced Monday it has acquired Stainless, a startup founded by former Stripe engineer Alex Rattray whose software is widely used by rival AI labs, including OpenAI and Google.
Anthropic did not disclose the terms of the deal. However, The Information reported last week that the company was in talks to acquire Stainless, which is backed by Sequoia Capital and Andreessen Horowitz, for more than $300 million.
The acquisition will take a key infrastructure supplier out of the hands of Anthropic’s competitors. The company told TechCrunch it will wind down all hosted Stainless products, including its SDK generator. An Anthropic spokesperson said Stainless customers will still own the SDKs they’ve generated to date and have full rights to modify and extend them however they wish.
The New York-based startup, founded in 2022, rose to prominence in the emerging AI industry for automating the creation and maintenance of software development kits, or SDKs—the libraries developers use to interact with APIs.
Rattray developed software that could take API specifications and turn them into production-ready SDKs across multiple programming languages, including Python, TypeScript, Kotlin, Go, and Java. It became a popular tool because the platform automatically updates the SDKs as APIs change, eliminating the time-consuming process of manually maintaining them.
The technology is particularly valuable to companies like Anthropic, OpenAI, Google, Replicate, Runway, and Cloudflare that are building AI agents that can connect to external software and complete tasks on behalf of users. Stainless’s SDK tools are an easy way to build and maintain those connections—but going forward, the tools will only be available to Anthropic, not its competitors.
According to Anthropic, Stainless software has powered the generation of every official Anthropic SDK since the earliest days of its API.
“I started Stainless because SDKs deserve as much care as the APIs they wrap,” Rattray said in a press release. “Anthropic was one of the first teams to bet on this with us. We have been watching what developers have built on Claude over the last few years, which made bringing our teams together an easy decision.”
[AgentUpdate Depth Analysis] Anthropic’s acquisition of Stainless is a masterclass in strategic moat-building. As the AI industry pivots from static chatbots to highly autonomous AI Agents, the ability to seamlessly connect models to external software is paramount. SDKs and APIs are the connective tissue of this new agentic web. By monopolizing Stainless’s automated SDK generation pipeline, Anthropic not only streamlines its own Model Context Protocol (MCP) ecosystem but also inflicts technical debt on rivals like OpenAI and Google, who must now manually maintain or reinvent their own SDK pipelines. This acquisition signals that the AI race has shifted from sheer parameter size to the efficiency of the developer experience, highlighting how foundational tooling will dictate which platform wins the allegiance of Agent builders.
