Anthropic Acquires Stainless, Locking Out OpenAI and Google

Anthropic Acquires Stainless, Locking Out OpenAI and Google

Quick Reads

• Anthropic has officially acquired Stainless, a New York-based SDK startup founded in 2022.
• The deal is reportedly valued at over $300 million, though Anthropic has not confirmed the figure.
• Stainless built the SDK tools that OpenAI, Google, Cloudflare, and Anthropic itself all relied on.
• Anthropic will wind down all hosted Stainless products, cutting access for rival companies.
• Existing Stainless customers retain full ownership and rights to the SDKs they already generated.

Anthropic acquires Stainless in a bold move that pulls a critical developer infrastructure tool directly out of its competitors’ hands. The AI company announced the deal on Monday, May 18, confirming it had taken ownership of the startup that quietly powered some of tech’s biggest names.

Stainless, founded by former Stripe engineer Alex Rattray, built software that transforms raw API specifications into production-ready SDKs. Specifically, the platform generates libraries in Python, TypeScript, Go, Java, Kotlin, and more. Furthermore, it automatically updates those SDKs whenever the underlying API changes, eliminating hours of manual maintenance for developer teams.

The technology mattered enormously to the AI industry. Companies like OpenAI, Google, Cloudflare, Runway, and Replicate all built on it. However, following this acquisition, those competitors lose access. Anthropic plans to wind down all hosted Stainless products and redirect the team’s work entirely toward the Claude platform.

Katelyn Lesse, Anthropic’s Head of Platform Engineering, said the company is excited to bring the Stainless team on board to advance Claude’s ability to connect to data and tools, noting that agents are only as useful as what they can connect to.

Rattray echoed that sentiment in the official announcement, saying he started Stainless because SDKs deserve as much care as the APIs they wrap, and that watching what developers built on Claude made the decision to join an easy one.

The acquisition aligns squarely with Anthropic’s push into AI agents. As the industry shifts from chatbot-style models to autonomous systems that act on behalf of users, reliable connections to external tools and APIs become foundational. According to Anthropic, Stainless software powered every official Anthropic SDK since the earliest days of its API. Moreover, the deal strips rivals of a tool they had long relied upon.

The terms remain undisclosed. Nevertheless, TechCrunch reported that The Information had pegged the deal at more than $300 million, roughly double Stainless’s last known valuation. Stainless was backed by Sequoia Capital and Andreessen Horowitz.

For existing Stainless customers, the company confirmed they retain full ownership of SDKs already generated, with complete rights to modify and extend them. Still, new signups, projects, and SDK generation are no longer available. Transition resources remain active at app.stainless.com/transition.

This acquisition signals something larger than a talent grab. Anthropic made it clear it intends to dominate the developer experience layer, not just the model layer, as the agentic AI race accelerates.