Anthropic has acquired Stainless in an effort to "improve developer experience and the connections between agents and external systems."

Stainless was founded in 2022 by Alex Rattray. The New York-based developer tools company that helps organizations build and maintain world-class software development kits (SDKs) and developer interfaces for their APIs, according to their LinkedIn.

"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," Rattay said.

"Stainless has shaped how developers experience the Claude API since the start, and it's been great to work with them on that," said Katelyn Lesse, head of Platform Engineering at Anthropic. "Agents are only as useful as what they can connect to. We're excited to bring the Stainless team into Anthropic to advance Claude's ability to connect to data and tools."

Stainless will be winding down its products, including its SDK generator and halting all new products, the firm said in a press release. The company’s clients previously included Google DeepMind, Meta and Anthropic's rival, OpenAI.

OpenAI originally built an internal software development kit, but later moved to Stainless' tooling after maintaining the system in-house became increasingly complex and resource-intensive. Stainless has also developed software tied to Anthropic's Model Context Protocol (MCP), a framework introduced in November 2024.

The transaction is worth approximately $300 million, The Information previously reported prior to the competition of the deal.

This acquisition comes as Anthropic is reportedly holding discussions with investors regarding a new funding round that would place the company’s valuation at $800 billion, more than doubling its $350 billion mark in February.

Anthropic’s annualized revenue reportedly hit $30 billion in April, surpassing OpenAI’s roughly $24 billion run rate. The company went from $9 billion at year-end 2025 to $30 billion in about four months, with over 1,000 companies now spending more than $1 million annually on Anthropic products.

The artificial intelligence company also recently launched Claude Mythos Preview, a model that can identify software vulnerabilities, to a small number of companies for testing.

The launch is reportedly so powerful that the company restricted access due to cybersecurity concerns, and this has only strengthened its positioning ahead of a potential IPO later this year.

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