Stainless helps OpenAI, Anthropic and others build SDKs for their APIs

Besides focusing on genetic AI, what do AI startups like OpenAI, Anthropic, and Together AI share in common? They use Stainlessa platform created by former Stripe executive Alex Rattray to build SDKs for their APIs.

Rattray, who studied economics at the University of Pennsylvania, has been building things for as long as he can remember, from an underground newspaper in high school to a bike-sharing program in college. Rattray picked up programming on the side while at UPenn, which led to a job at Stripe as an engineer on the developer platform team.

At Stripe, Rattray helped revamp the API documentation and release the system that powers Stripe’s API client SDK. While working on these projects Rattray noticed that there was no easy way for companies, including Stripe, to build SDKs for their APIs at scale.

“The SDK script was not scalable,” he told TechCrunch. “Today, every API designer has to re-arrange a million questions and painstakingly enforce consistency around those decisions in their API.”

Now, you might be wondering, why does a company need an SDK if they offer an API? APIs are simple protocols that allow software components to communicate with each other and transfer data. SDKs, on the other hand, offer a set of software creation tools that connect to APIs. Without an SDK to accompany an API, API users are forced to read the API docs and build everything themselves, which isn’t the best experience.

Rattray’s solution is Stainless, which takes an API specification and builds SDKs in a range of programming languages, including Python, TypeScript, Kotlin, Go and Java. As APIs evolve and change, Stainless’s platform promotes these updates with options to release and publish changelogs.

“API companies today have a multi-person team building libraries in every new language to connect to their API,” Rattray said. “These libraries inevitably become inconsistent, out of date, and require constant changes by expert engineers. Stainless fixes this problem by creating them via code.”

Stainless isn’t the only API-to-SDK generator out there. There’s LibLab and Speakeasy, to name a couple, as well as long-standing open source projects like OpenAPI Generator.

Stainless steel, however, offers more “shininess” than most others, Rattray said, thanks in part to the use of genetic artificial intelligence.

“Stainless uses genetic AI to create an initial ‘Stainless config’ for customers, which is then up to them to adapt to their API,” he explained. “This is especially valuable for AI companies, whose huge user bases include many novice developers trying to integrate with complex features like chat flow and tools.”

Perhaps that’s what attracted customers like OpenAI, Anthropic and Together AI, along with Lithic, LangChain, Orb, Modern Treasury and Cloudflare. Stainless has “dozens” of paying customers in its beta, Rattray said, and some of the SDKs it builds, including OpenAI’s Python SDK, get millions of downloads a week.

“If your company wants to be a platform, your API is the foundation of that,” he said. “Great SDKs for your API lead to faster integration, broader feature adoption, faster upgrades, and confidence in the quality of your engineering.”

Most customers pay for the Stainless enterprise tier, which comes with additional white-glove services and AI-specific functionality. Publishing an SDK with Stainless is free. However, companies have to pay between $250 per month and $30,000 per year for multiple SDKs in multiple programming languages.

Rattray bootstrapped Stainless “with revenue from day one,” he said, adding that the company could be profitable as soon as this year. Annual recurring revenue hovers around $1 million. But Rattray chose instead to take on outside investment to create new product lines.

Stainless recently closed a $3.5 million seed round with participation from Sequoia and The General Partnership.

“Across the technology ecosystem, Stainless stands out as a beacon that elevates the developer experience, rivaling the high standards once set by Stripe,” said Anthony Kline, partner at The General Partnership. “As APIs continue to be the key building blocks for integrating services like LLMs into applications, Alex’s first-hand experience pioneering Stripe’s coded API system uniquely positions him to build Stainless into the quintessential platform for seamless, high-quality API interactions’.

Stainless has a team of 10 people based in New York. Rattray expects the number of employees to grow to 15 or 20 by the end of the year.