Stainless

Stainless is a developer platform that generates robust, idiomatic client libraries, documentation sites, MCP servers, CLIs, and Terraform providers directly from an OpenAPI specification. Founded in New York and backed by Sequoia, the company draws on experience from Stripe, Heroku, and Twilio to help API companies deliver polished developer experiences at scale. In May 2026, Stainless announced it is joining Anthropic and winding down its hosted products.

What It Is

Stainless sits in the API developer tooling category, specifically the SDK generation and API documentation space. API companies provide an OpenAPI spec; Stainless reads it and outputs production-ready client libraries in multiple languages, a hosted documentation site, an MCP server for agent integrations, a CLI tool, and a Terraform provider — all kept in sync as the API evolves. The core value proposition is eliminating the manual effort of writing and maintaining SDKs across many languages while ensuring the output meets the quality bar of hand-crafted libraries like those Stripe is known for.

What Gets Generated

From a single OpenAPI spec, Stainless can produce:

• SDKs in TypeScript, Python, Go, Java, Kotlin, Ruby, C#, and PHP
• API documentation with custom domains, AI markdown rendering, AI chat, password protection, and a complete component library
• MCP servers for agent-native API access
• CLI tools — production-ready command-line interfaces
• Terraform providers — infrastructure-as-code integrations
• Preview builds in CI for iterating before publishing

Generated SDK code is published under the Apache 2.0 license and is owned by the customer.

How the Workflow Fits Together

Teams connect their OpenAPI spec to Stainless via the web Studio or the CLI. Stainless generates code into staging GitHub repositories for internal testing, then publishes to the customer's own GitHub organization when ready. The platform handles webhooks, streaming, async patterns, authentication, headers, and unit tests automatically. Custom code can be injected into limited files. GitHub member sync keeps access controls aligned with the customer's organization.

Audience and Adoption Signal

The platform targets API-first companies that need to support developers across multiple programming languages without dedicating engineering resources to SDK maintenance. The pricing page lists customers including Anthropic, OpenAI, Cloudflare, Google DeepMind, Perplexity, Replicate, Runway, LangChain, Groq, DigitalOcean, and dozens of others — these are vendor-published customer references. TechCrunch reported on a Sequoia seed round in April 2024, noting Stainless was already working with OpenAI and Anthropic at that time.

Update: Stainless Joining Anthropic

On May 18, 2026, founder and CEO Alex Rattray announced that Stainless is joining Anthropic to work on the Claude Platform team, focused on Claude Platform capabilities and connecting agents to APIs. As part of the transition, Stainless is winding down all hosted products, including the SDK generator. New signups, projects, and SDKs are no longer available.

Existing customers are directed to app.stainless.com/transition for guidance on moving off Stainless-managed products. Customers retain full rights to SDKs already generated and can modify or extend them however they wish. Stainless was one of Anthropic's earliest API partners, having collaborated on nearly every Claude API launch since the company's founding in 2022.