NEW YORK — Stainless, which makes software for developers to easily use APIs, has raised $25 million in Series A funding, led by Jennifer Li at a16z with participation from existing investors including Sequoia and The General Partnership. In addition, investors also include Felicis, Zapier, MongoDB Ventures, and Claire Hughes Johnson (former Stripe COO) and Amit Agarwal (Datadog President).
Founded in 2022, Stainless says its software development kit (SDK) is being used for top AI model providers such as OpenAI, Anthropic, and Meta (Llama models), fast-growing fintech businesses like Metronome, Modern Treasury, and Orb, as well as developer-first platforms like Cloudflare and Mux. These are all powered by Stainless.
Using Stainless, companies can build world-class API DX without dedicating full-time engineers to SDK maintenance. Their SDKs are consistent across languages, up-to-date, and easy for developers to use, even with rapidly changing APIs.
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. Building an SDK that feels native to each programming language—something developers actually want to use—is a massive challenge.