Anthropic announced on May 18, 2026, that it has acquired Stainless, a startup founded in 2022 that develops SDK and MCP server tooling for APIs [1]. Stainless’ software has powered the generation of every official Anthropic SDK since the earliest days of its API, converting API specifications into SDKs for TypeScript, Python, Go, Java, Kotlin, and others [2, 1].
Stainless was founded by Alex Rattray, a former Stripe engineer, who said he started the company because “SDKs deserve as much care as the APIs they wrap.” He added that Anthropic was one of the first teams to support the project and that joining forces made “bringing our teams together an easy decision” [2, 1].
Anthropic plans to wind down all hosted Stainless products, including its SDK generator, making these tools available exclusively for internal Anthropic use going forward. Customers who have already generated SDKs with Stainless retain the rights to those SDKs and can continue to modify them as they wish [1].
Katelyn Lesse, Head of Platform Engineering at Anthropic, said: “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” [2].
The acquisition price was reported by The Information to be over $300 million [1]. Through this integration, Anthropic aims to deepen Claude’s capacity to interface with external data sources and software tools by leveraging Stainless’ expertise.
Stainless was founded in 2022 and quickly became a key partner in powering Anthropic’s SDK ecosystem [2, 1]. The official acquisition announcement came on May 18, 2026, marking the startup’s transition into Anthropic’s platform engineering division [1].
