Stainless Secures $25 Mn Series A Funding for API Integration

NYC-based Stainless, a tech startup focused on API integration, has raised $25 million in Series A funding. The round was led by a16z, with support from Sequoia, The General Partnership, and others like Felicis, Zapier, and MongoDB Ventures. The funding highlights the rising demand for strong API tools.

With the new funding, Stainless plans to expand its team and further enhance its platform, addressing rising developer expectations and the evolving role of APIs in agentic AI. The company’s vision is to become the go-to solution for all API-related development.

Founded in 2022, Stainless aims to simplify how developers work with APIs through its Stainless SDK generator. It creates high-quality, multi-language SDKs tailored to developers’ needs, making API integration simple across industries. 

“APIs are everywhere. They power your favorite apps, enable breakthrough AI experiences, and facilitate secure financial transactions. But for developers, the experience of integrating with APIs hasn’t kept up with their importance,” said Alex Rattray, founder at Stainless. The company’s auto-generated SDKs let customers focus on building great APIs.

Stainless powers SDKs for leading AI platforms like OpenAI, Anthropic, and Meta, as well as fintech companies such as Modern Treasury and Orb. Developer-focused platforms like Cloudflare and Mux also rely on Stainless, which handles complex tasks like auto-pagination, retries, and version management.

The rise of AI has made this even more critical. With AI agents performing thousands of API calls based on specifications and documentation, there’s minimal tolerance for poorly designed SDKs. A bad SDK can disrupt agent workflows, explained Jennifer Li, lead partner at a16z.