Anthropic buys Stainless, drops confidentiality to expand Mythos developer tools

Anthropic said on May 18 that it had acquired Stainless, a startup whose software generates developer kits and Model Context Protocol, or MCP, server tooling, in a move the company said would deepen Claude’s links to outside data and tools. The San Francisco-based AI company disclosed the deal in a blog post and said Stainless had powered every official Anthropic SDK since the early days of its API. (anthropic.com) Anthropic did not disclose financial terms. On the same day, Anthropic’s cybersecurity initiative around Claude Mythos Preview also moved toward broader information sharing with partners already involved in its Project Glasswing program, according to Anthropic materials and social posts referenced in the briefing. (stainless.com) ### Why did Anthropic buy a company that already built its SDKs? Anthropic said Stainless had been a long-running supplier and that the acquisition was meant to extend Claude from “models that answer” toward agents that can act across software systems. In its announcement, Anthropic described Stainless as “a leader in SDKs and MCP server tooling” and said agents are only as useful as the systems they can reach. Katelyn Lesse, Anthropic’s head of platform engineering, said Stainless had shaped how developers experience the Claude API “since the start.” Lesse said Anthropic wanted to bring the team in-house to advance Claude’s ability to connect to data and tools. (anthropic.com) ### What exactly does Stainless make? Stainless said on May 18 that it was founded in early 2022 to automate the generation and maintenance of SDKs and improve developer experience around APIs. Anthropic said the company turns an API specification into SDKs across TypeScript, Python, Go, Java and Kotlin, among other languages. Alex Rattray, Stainless’s founder and chief executive, said he started the company because “SDKs deserve as much care as the APIs they wrap.” Stainless said it had worked “hand-in-hand” with Anthropic on nearly every Claude API launch. (anthropic.com) ### What changes for Stainless customers now? (anthropic.com) Stainless said starting May 18 it would wind down all hosted products, including its SDK generator. The company said new signups, projects and SDKs would no longer be available and directed customers to a transition page for next steps. Stainless also said customers would keep ownership of SDKs they had already generated and would retain full rights to modify and extend them. (anthropic.com) Anthropic told TechCrunch the same, while TechCrunch reported that Stainless tools had also been used by companies including OpenAI, Google and Cloudflare. ### How does Mythos fit into this deal? Anthropic’s Project Glasswing, announced on April 7, is built around Claude Mythos Preview, which the company described as its most capable model yet for coding and agentic tasks. Anthropic said launch partners including Amazon Web Services, Microsoft, Apple, Cisco, CrowdStrike, Google, JPMorganChase, Nvidia and Palo Alto Networks were using Mythos Preview in defensive security work. (stainless.com) Anthropic said as part of Glasswing it would share what it learns so “the whole industry can benefit,” and it extended access to more than 40 additional organizations that build or maintain critical software infrastructure. Anthropic also committed up to $100 million in usage credits and $4 million in donations to open-source security groups. (stainless.com) ### What has Anthropic said about Mythos’s capabilities? Anthropic said in an April 7 technical post that Claude Mythos Preview had identified and exploited zero-day vulnerabilities in every major operating system and every major web browser during testing. The company said more than 99% of the vulnerabilities it found had not yet been patched, which limited what it could publicly disclose. (anthropic.com) Project Glasswing materials say AWS and other partners are already testing Mythos Preview on critical codebases. Amy Herzog, vice president and chief information security officer at AWS, said Anthropic’s model was helping strengthen code in Amazon’s own security operations. (anthropic.com) ### What happens next? May 18 is the effective date Anthropic and Stainless gave for the acquisition announcement and for the shutdown of new Stainless hosted signups. Project Glasswing remains active with named partners including AWS and Microsoft, and Anthropic’s next public updates are likely to appear on its newsroom and Project Glasswing pages, where the company has been posting announcements and partner details. (red.anthropic.com) (anthropic.com 1) (anthropic.com 2)