Anthropic Buys Stainless, a Key Developer Tools Startup
Anthropic has acquired Stainless, a New York-based developer tools startup known for software that helps companies generate and maintain software development kits, or SDKs.
The startup was founded in 2022 by Alex Rattray, a former Stripe engineer. Stainless became widely used across the AI industry, including by companies such as OpenAI, Google, Replicate, Runway, Cloudflare, and Anthropic itself.
Anthropic did not disclose the terms of the deal. The Information reported that Anthropic had been in talks to buy Stainless, which is backed by Sequoia Capital and Andreessen Horowitz, for more than $300 million.
Why Stainless Became Important in AI Infrastructure
Stainless built software that automates the creation and upkeep of SDKs. These SDKs are the libraries developers use to work with APIs, which makes them a practical layer between software products and the developers building on top of them.
The core Stainless product could take API specifications and turn them into production-ready SDKs across several programming languages, including:
- Python
- TypeScript
- Kotlin
- Go
- Java
That mattered because SDK maintenance can be time-consuming. When APIs change, SDKs often need to change with them. Stainless made that process easier by automatically updating SDKs as APIs evolved, reducing the manual work normally required to keep them current.
What the Acquisition Means for Stainless Products
The deal removes a key infrastructure supplier from the broader market, including from the reach of Anthropic’s competitors.
Anthropic said it will wind down all hosted Stainless products, including the company’s SDK generator. Going forward, Stainless tools will be available to Anthropic rather than to competing companies that had used the platform.
An Anthropic spokesperson said Stainless customers will continue to own the SDKs they have generated so far. Those customers also retain full rights to modify and extend those SDKs however they wish.
Why SDK Generation Matters for AI Companies
Stainless’ technology is especially useful for companies building AI agents that connect to external software and complete tasks on behalf of users.
Companies such as Anthropic, OpenAI, Google, Replicate, Runway, and Cloudflare have been building systems where reliable software connections matter. SDK tools help build and maintain those connections more easily, which makes Stainless valuable infrastructure in the AI ecosystem.
By acquiring Stainless, Anthropic is bringing that capability inside its own organization.
Stainless and Anthropic’s Existing Relationship
Stainless had already played an important role in Anthropic’s developer ecosystem. According to Anthropic, Stainless software powered the generation of every official Anthropic SDK from the earliest days of Anthropic’s API.
Rattray said Stainless was built around the idea that SDKs deserve the same level of care as the APIs they wrap. He also said Anthropic was one of the first teams to support that approach, and that watching developers build on Claude made bringing the two teams together an easy decision.
How the Deal Changes Access for Competitors
The most immediate shift is availability. Stainless tools had been used by rival AI labs and infrastructure companies, but Anthropic said the hosted products will be wound down.
That means competitors that previously relied on Stainless will no longer have access to those hosted tools going forward. They will keep ownership and usage rights over the SDKs already generated, but the Stainless platform itself is being folded into Anthropic’s work.