We’re excited to share that we’ve 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, we’re thrilled to welcome Felicis, Zapier, MongoDB Ventures, and some amazing operators, including Claire Hughes Johnson (former Stripe COO) and Amit Agarwal (Datadog President).

Since launching our first product, the Stainless SDK generator, we’ve been blown away by adoption across a wide variety of companies and industries—SDKs 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, are all powered by Stainless.

This milestone isn’t only about funding—it’s a vote of confidence in the future and vision we’re building, and we’re grateful for the partnership of our investors, customers, and community.

Why we started Stainless

When we started Stainless in early 2022, our vision was simple: make it effortless for developers to work with APIs. We’re still in the early innings here.

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.

At Stripe, I saw this problem firsthand while leading efforts on API docs and SDK tooling. Most companies couldn’t afford to invest in world-class DX. The tooling either didn’t exist, the tradeoffs were too painful, or the code quality was inconsistent—like it had been run through a machine translator versus being handcrafted by experienced engineers.

That’s why we built the Stainless SDK generator, which delivers the quality and usability developers demand.

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.

And when companies offer Stainless-powered SDKs, they’re able to dramatically reduce the work needed to integrate with their APIs.

How companies use Stainless today

Stainless generates the SDKs for some of the internet's most demanding APIs.

Top AI platforms including OpenAI, Anthropic, Runway, and Meta’s Llama Stack trust Stainless to power their SDKs. (Not to miss the party, Google’s Gemini models interoperate with OpenAI’s SDKs—and are the preferred integration path!) Beyond model providers, Groq, Cerebras, LangChain, Braintrust, Writer and many other fast-growing platforms also choose to improve the DX of their APIs with Stainless. Collectively, millions of AI developers alone download Stainless-built SDKs every single week.

For developer infrastructure companies, APIs are the primary interface for their customers. Take for example, Cloudflare: when they introduce new APIs, they've found that user adoption is heavily impacted by SDK support—if a new feature or product doesn’t make it into a user’s preferred language SDK, it’s as good as non-existent.

In the span of a few months, we’ve gone from inconsistent, manually maintained SDKs to automatically shipping over 1,000 endpoints across three language SDKs with hands-off updates.

‍— Jacob Bednarz, API Platform Tech Lead, Cloudflare

We hear similar stories from our API-first customers in fintech, such as Modern Treasury, Metronome, Orb, or Lithic. Even in regulated industries like banking, Stainless is setting the standard for secure, high-quality developer tools.

We’ve just scratched the surface and are excited to see how companies across a variety of industries use Stainless in the months and years ahead.

How it works

At its core, Stainless takes your OpenAPI spec and produces SDKs that developers love. We’ve obsessed over details like:

• Rich typing: Autocomplete, inline docs, and more.
• Auto-pagination & retry: Handling complexity so developers don’t have to.
• Multi-language support: TypeScript, Python, Go, Java, and more.

Producing a good SDK is more involved than many developers realize. The details matter, and it’s not just about pretty code—it’s about making the right choices and balancing tradeoffs between the characteristics of REST APIs and the idioms of each language.

We don’t just generate code—we maintain it. As your API evolves, we push updates, manage versioning, and generate changelogs. The result? Developers get SDKs that feel handcrafted, while your team focuses on building the API itself.

What’s next

Every company is becoming an API company, and developer expectations are higher than ever. As APIs become more sophisticated, maintaining up-to-date and consistent SDKs across multiple languages becomes increasingly challenging. Stainless already addresses this by automating updates and versioning, ensuring that developers always have access to the latest API features without the overhead of manual maintenance.

And as we enter a future of agentic AI, where autonomous systems perform tasks and make decisions, the role of APIs will become more critical than ever to make data and capabilities from various services more accessible to AI. AI agents will rely on (and will favor) robust, well-designed APIs to interact with various services and data sources, enabling them to execute complex workflows.

SDKs are just the start. Our vision is to build a comprehensive platform that developers turn to for everything API-related.

Join us!

We’re growing our team (we all still fit on a single floor in NYC!) and we’re hiring across technical and business roles. If our vision resonates with you, we’d love to have you on board.

And if you’re interested in exploring Stainless for your company, get started with the docs or please reach out!

A special thank you

To our customers, partners, and the developer community: thank you for trusting us. Your support and feedback push us to raise the bar. And to the teams at a16z, Sequoia, Felicis, The General Partnership, Zapier, MongoDB Ventures and our stellar angel investors: we’re thrilled to have you alongside us for this journey.

— Alex Rattray, on behalf of the Stainless team

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