What do AI startups like OpenAI, Anthropic and Together AI have in common besides their focus on generative AI? They use Stainless, a platform developed by former Stripe employee Alex Rattray, to generate SDKs for their APIs.
Rattray, who studied economics at the University of Pennsylvania, has been building for as long as he can remember, from an underground newspaper in high school to a bike share program in college. While at UPenn, Rattray began coding on the side, which led to a job at Stripe as an engineer on the developer platform team.
At Stripe, Rattray helped revise the API documentation and introduce the system underlying Stripe’s API client SDK. While working on these projects, Rattray discovered that there was no easy way for companies, including Stripe, to build SDKs for their APIs at scale.
“Handwritten, the SDKs didn’t scale,” he told TechCrunch. “Today, every API designer has to revisit a million and one bikeshed questions and painstakingly enforce the consistency of those decisions across their API.”
Now you may be asking yourself: Why would a company need an SDK when they offer an API? APIs are simply protocols that allow software components to communicate with each other and transfer data. SDKs, on the other hand, provide a set of software creation tools that can be integrated with APIs. Without an SDK to accompany an API, API users are forced to read API docs and build everything themselves, which isn’t the best experience.
Rattray’s solution is Stainless, which takes an API specification and generates SDKs in a range of programming languages, including Python, TypeScript, Kotlin, Go and Java. As APIs evolve and change, Stainless’s platform supports these updates with versioning and changelog publishing options.
“API companies today have a team of multiple people building libraries in each new language to connect to their API,” Rattray said. “These libraries inevitably become inconsistent, outdated and require constant modifications by specialist engineers. Stainless solves this problem by generating them via code.”
Stainless isn’t the only API to SDK generator on the market. There’s LibLab and Speakeasy, to name a few, as well as long-standing open source projects like OpenAPI Generator.
However, Stainless delivers more “shine” than most, Rattray said, thanks in part to its use of generative AI.
“Stainless uses generative AI to create an initial ‘Stainless configuration’ for customers, which is then up to them to optimize their API,” he explained. “This is particularly valuable for AI companies, whose huge user base includes many inexperienced developers trying to integrate complex features like chat streaming and tools.”
Perhaps that’s what attracted customers like OpenAI, Anthropic and Together AI, as well as Lithic, LangChain, Orb, Modern Treasury and Cloudflare. Rattray said Stainless has “dozens” of paying customers in its beta, and some of the SDKs it generates, including OpenAI’s Python SDK, are downloaded millions of times a week.
“If your company wants to be a platform, your API is the foundation of it,” he said. “Great SDKs for your API ensure faster integration, broader feature adoption, faster upgrades, and confidence in your technical quality.”
Most customers pay for Stainless’s Enterprise tier, which offers additional white-glove services and AI-specific features. Publishing a single SDK with Stainless is free. However, multiple SDKs in multiple programming languages require companies to spend between $250 per month and $30,000 per year.
Rattray has made Stainless “revenue from day one,” he said, adding that the company could be profitable as early as this year; Annual recurring revenue is around $1 million. However, Rattray decided instead to take on outside investment to build 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 and rivals Stripe’s high standards,” said Anthony Kline, partner at The General Partnership. “As APIs continue to be the core building blocks of integrating services like LLMs into applications, Alex’s first-hand experience as a pioneer of Stripe’s API code generator system puts him in a unique position to make Stainless the quintessential platform for seamless, high-quality to make high-quality API interactions.”
Stainless has a 10-person team based in New York. Rattray expects the number of employees to increase to 15 to 20 by the end of the year.