Anthropic acquires Stainless to lock down SDK infrastructure from rivals

At a glance:

• Anthropic has bought Stainless, the SDK-generation startup whose tools are used by OpenAI, Google, and Cloudflare, reportedly for more than $300 million.
• Anthropic will shut down Stainless's hosted products, including its SDK generator, and the technology will become exclusive to Anthropic.
• Stainless, founded in 2022 by former Stripe engineer Alex Rattray, automates the creation and maintenance of SDKs across Python, TypeScript, Kotlin, Go, and Java.

The deal and what happens next

Anthropic announced Monday that it has acquired Stainless, a New York-based developer-tools startup founded in 2022 by Alex Rattray, a former Stripe engineer. The terms of the deal were not disclosed, but The Information reported last week that Anthropic was in talks to buy Stainless for more than $300 million. Stainless is backed by Sequoia Capital and Andreessen Horowitz.

In a move that signals Anthropic's intent to lock down a critical piece of AI-infrastructure supply chain, the company told TechCrunch it will wind down all hosted Stainless products, including the SDK generator. An Anthropic spokesperson said existing Stainless customers will retain ownership of the SDKs they have generated to date and will have full rights to modify and extend them however they wish. Going forward, however, the tools will be available only to Anthropic and its own developers.

Rattray said in a press release: "I started Stainless because SDKs deserve as much care as the APIs they wrap. 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. The team gets to keep doing the work we love, on the platform where it matters most."

What Stainless actually does

Stainless 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 can take API specifications and turn them into production-ready SDKs across multiple programming languages, including Python, TypeScript, Kotlin, Go, and Java.

The platform's key differentiator is its ability to automatically update SDKs as APIs change, eliminating the time-consuming process of manually maintaining them. According to Anthropic, Stainless software has powered the generation of every official Anthropic SDK since the earliest days of its API.

This kind of tooling is particularly valuable to companies building AI agents that need to connect to external software and complete tasks on behalf of users. The list of Stainless customers reads like a who's who of the AI and infrastructure space: OpenAI, Google, Anthropic, Replicate, Runway, and Cloudflare all relied on Stainless to build and maintain the SDK connections that power their agent workflows.

Why it matters for the competitive landscape

The acquisition removes a key infrastructure supplier from the hands of Anthropic's competitors. For years, Stainless has been a neutral utility — a developer tool that any company with an API could plug into. By absorbing Stainless, Anthropic is converting a shared resource into a proprietary asset.

The move echoes a broader trend in the AI industry where companies are racing to control the foundational tooling that underpins their platforms. SDKs are the connective tissue between AI models and the external services they call upon; whoever controls the SDK generation pipeline effectively controls how third-party developers build on top of their platform.

For the startups and enterprises that depended on Stainless, the change is immediate. They will need to either self-host the tools, find an alternative provider, or build their own SDK generation pipelines. The fact that Anthropic is allowing customers to keep the SDKs they have already generated provides some continuity, but the hosted product — the engine that continuously updates those SDKs as APIs evolve — will no longer be available to them.

What to watch next

The deal also raises questions about the future of Stainless's open developer community. The startup had built a reputation as a developer-friendly company, and its SDK generation pipeline was widely regarded as best-in-class. Whether Anthropic will open-source any part of the codebase or continue to serve the broader developer ecosystem remains to be seen.

For investors and industry observers, the $300 million-plus price tag underscores how much value the market places on developer tooling at this stage of the AI build-out. As more companies deploy agentic AI systems that require reliable, multi-language SDKs, the ability to generate and maintain those SDKs automatically becomes a strategic asset — one Anthropic is now unwilling to share.

Tags

• Anthropic
• Stainless
• SDK generation
• developer tools
• AI agents
• OpenAI