Anthropic Buys the SDK Startup Used by OpenAI and Google

Anthropic acquired Stainless, a New York-based startup that automates the generation of production SDKs and server tooling. The May 18, 2026 transaction brings the infrastructure powering the industry’s most popular AI libraries directly under Anthropic’s control. The acquisition is designed to accelerate the deployment of the Model Context Protocol (MCP), embedding Anthropic into the foundational tooling layer that connects AI agents to external data.

Automating API Infrastructure

Stainless operates as an AI-powered compiler, converting OpenAPI specifications into idiomatic, production-ready SDKs. Maintaining typed client libraries across multiple languages requires significant engineering overhead, especially for platforms with rapidly evolving API surfaces. Stainless solved this constraint by generating reliable client code directly from raw specification files.

The 20-person company, founded by former Stripe engineer Alex Rattray, outputs strictly typed libraries across TypeScript, Python, Go, Java, and Kotlin. Prior to the acquisition, Stainless had focused heavily on building developer infrastructure for the Model Context Protocol, an open standard Anthropic launched in late 2024. By bringing the Stainless team in-house, Anthropic gains the technical capability to automate the creation of MCP servers. This reduces the friction developers face when exposing internal enterprise APIs and local filesystems to Claude models.

Managing Competitor Distribution

The strategic leverage of this acquisition stems from Stainless’s existing customer base. The startup currently builds and maintains the official API packages for Anthropic’s primary rivals. When a developer runs a standard package installation for OpenAI or implements Google’s Gemini API surface, they are integrating code compiled by Stainless.

The client roster also includes Meta’s Llama Stack and Cloudflare’s API infrastructure. The underlying architecture of these generated SDKs dictates how critical network features behave in production, including streaming, timeout configurations, and error handling. Operating this specific distribution infrastructure gives Anthropic theoretical control over the tooling layer that millions of developers rely on to interact with competing models.

Ecosystem Expansion

This marks Anthropic’s fourth acquisition in a six-month window, reflecting a rapid build-out of a comprehensive developer ecosystem. The company previously absorbed the JavaScript runtime Bun in December 2025, AI computer-use startup Vercept in February 2026, and biotech startup Coefficient Bio in April.

While official financial terms were not published in Anthropic’s release, the transaction reportedly values Stainless at over $300 million, more than doubling the startup’s $150 million valuation from December 2024. This aggressive expansion of developer tooling aligns with Anthropic’s broader capital strategy as the company reportedly pursues a $900 billion valuation in its upcoming funding round.

If you maintain API infrastructure or build multi-agent systems, Anthropic’s consolidation of SDK generation signals that MCP is becoming a baseline requirement rather than an optional capability. Development teams should prepare their internal API definitions for automated MCP server generation, as the tooling layer connecting proprietary data to agentic workflows is rapidly standardizing.