Anthropic said it is acquiring SDK generation company Stainless for about $300 million, bringing a quiet but important piece of AI developer infrastructure in-house. Stainless has built tooling not only for Anthropic, but also for OpenAI, Google, Cloudflare, Runway, Replicate, and Meta. After the deal, the Stainless team will join Anthropic’s platform engineering organization, and the company plans to wind down Stainless’ hosted services over time.
A backend tooling company used across the AI industry
Stainless focuses on turning API specification files into usable SDKs, sparing developers from manually handling HTTP requests, error logic, and response parsing. Its system can generate SDKs for TypeScript, Python, Go, Java, and Kotlin, along with CLI tools and MCP servers. That makes it part of the plumbing behind how developers actually integrate model APIs into products.
The company was founded in 2022 by Alex Rattray, who came from Stripe’s developer platform team. Stripe has long been treated as a benchmark for API developer experience, and Stainless applied that philosophy to AI-era tooling. The startup has backing from Sequoia Capital and a16z.
Why Anthropic wanted Stainless inside the company
Anthropic framed the acquisition around utility: agents matter only if they can connect to data and tools. Model performance has improved fast, but practical use still depends on whether a system can reach databases, call external APIs, and interact with third-party services. Stainless had already helped shape the developer experience around the Claude API from the early stage, which helps explain why Anthropic moved to acquire the whole team.
Katelyn Lesse, who leads platform engineering at Anthropic, said Stainless had been involved with Claude API tooling from the beginning. Folding that capability into Anthropic gives the company tighter control over how Claude connects to external systems, rather than relying on an outside vendor.
What changes for other customers
The competitive angle is hard to miss. Stainless had been producing SDKs and related tooling for OpenAI, Google, Cloudflare, Runway, Replicate, and Meta as well. Anthropic said existing customers will retain full rights to the SDKs already generated, but new business will stop as Stainless’ hosted offering is phased out.
That leaves rivals looking for internal replacements or outside alternatives. Anthropic, meanwhile, ends up controlling three linked layers at once: the MCP protocol layer, the Stainless tooling generation layer, and the Claude model layer. Current Claude SDKs will keep being maintained, and the buildout around the MCP ecosystem is expected to accelerate under the combined team.