For three years, Stainless did work that almost nobody outside software engineering noticed. Founded in 2022 by former Stripe engineer Alex Rattray, it automated the creation of software development kits: the libraries that sit between an API and the developers trying to use it. Without tooling like this, maintaining SDK parity across languages requires parallel engineering work every time an API changes. Stainless solved that by generating SDKs across TypeScript, Python, Go, Java, Kotlin, and more from a single specification, with each one built to feel native in its language.
Stainless powered every official Anthropic SDK from the earliest days of the Claude API and counted Cloudflare, Google, and OpenAI among its clients. On 18 May 2026, Anthropic acquired the company in a deal reported to be worth more than $300 million.
Why Anthropic Needed to Own Its SDK and MCP Infrastructure
Alongside SDKs, Stainless generates MCP servers: the connectors that link AI agents to external APIs. MCP, the Model Context Protocol, is the open standard Anthropic introduced in November 2024. As UC Today has covered, MCP separates an agent’s reasoning from its actions. Rather than firing raw API calls with unpredictable results, agents operate through defined inputs, outputs, and scoped permissions. That structure is what makes agentic AI deployable at enterprise scale.
Adoption has been broad and fast. OpenAI incorporated MCP into its own Agents SDK in March 2025. The protocol is now embedded across Salesforce’s Agentforce and Zoom’s AI Companion. In December 2025, Anthropic donated the protocol to the Agentic AI Foundation, a directed fund under the Linux Foundation co-founded by Anthropic, Block, and OpenAI. UC Today’s coverage of Salesforce’s Agent Fabric expansion showed automatic agent discovery now spanning MCP servers alongside Amazon Bedrock and Microsoft Foundry. Stainless generates the servers that sit behind all of it, using the same API specification it uses to produce SDKs.
With this acquisition, Anthropic controls the model, the connectivity standard, and the toolchain that builds connections in practice. Katelyn Lesse, Anthropic’s Head of Platform Engineering, put it directly:
“Stainless has shaped how developers experience the Claude API since the start, and it’s been great to work with them on that. 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.”
What the Deal Means for Enterprise AI Agent Connectivity
For enterprise buyers, the connectivity question is already live. The 2026 Connectivity Benchmark Report, produced by Salesforce with Vanson Bourne and Deloitte Digital, found that 68% of IT leaders struggle to keep pace with emerging agent standards including MCP. Enterprises currently run an average of 12 agents, with that number projected to grow 67% within two years.
In practice, each agent deployment depends on clean, reliable connections. An agent handling IT service requests needs consistent access to a ticketing system. One supporting a sales team needs live CRM data. One managing project updates needs reliable read-write access to a project management platform. Each of those connections runs through an SDK or an MCP server. As a result, the quality of that underlying tooling has a direct bearing on whether agents perform as expected in production.
Developer tooling has typically been a background concern for enterprise buyers. However, as agent deployments scale and governance becomes a primary IT challenge, the infrastructure underpinning every agent connection becomes a more significant variable in platform selection.
Rattray explained what the deal meant for his team:
“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.”
Stainless Also Built OpenAI’s SDKs. What Happens Next?
Stainless generated SDKs for OpenAI as well as Anthropic. OpenAI’s public product pages confirm the relationship. Anthropic has not made any statement about third-party client relationships going forward, saying only that the Stainless team will continue its existing work within Anthropic.
For teams building on Claude, the practical effect is tighter alignment between model updates and developer tooling. SDK and MCP server development now sits inside the same organisation that builds the model. For the broader ecosystem, the more significant question is how the market for independent SDK and MCP tooling develops now that one of its most capable players has moved inside a major AI platform.
