Developers expect technology vendors to provide software development kits (SDKs) with their products, making it easy to create apps using those products. However, many vendors only offer APIs, which are simply protocols that allow software components to communicate with each other.
Stainless founder Alex Rattray believes AI can help in this area. Stainless uses AI to automatically generate SDKs from APIs, primarily on the fly.
As Rattray explained to TechCrunch, without an SDK, API users would have to read the API documentation and build everything themselves. However, there is no easy way for vendors to create SDKs for their APIs at scale.
Stainless takes API specifications and generates SDKs in a variety of programming languages, including Python, TypeScript, Kotlin, and Go. As APIs evolve and change, Stainless' platform pushes those updates using version control and changelog publishing options.
While a typical vendor might have in-house developers building libraries in different languages to connect to the API, Stainless uses AI to create the initial configuration and then let the team adapt it to the API. You can fine-tune it. Rattray claims this avoids issues such as inconsistent or outdated libraries, allowing for faster upgrades and faster integration.
“We are rapidly entering a world where everyone has access to expert-level engineering in their pocket,” he said. “That change will force all companies with websites to grow their APIs from a feature for power users to the primary interface for all users, and will encourage all companies without good APIs to would be as anachronistic as a restaurant without a website.”
Many of Stainless's features are based on Rattray's experience in the industry.
Image credit: Stainless Steel
An economics major, Rattray learned programming on the side while attending UPenn, which led to him landing a job at Stripe as an engineer on the developer platform team. At Stripe, Rattray helped revamp API documentation and launch a system to power Stripe's API client SDK.
Stainless isn't the only API-to-SDK generator. There are long-standing open source projects such as LibLab and Speakeasy, as well as OpenAPI Generator, to name a few.
But Rattray argues that stainless steel is becoming more “sophisticated” thanks to AI.
“While OpenAPI Generator exists, many customers say they tried it, but the code quality of the output was noticeably poor. Editing the output to get it to a satisfactory state requires further It often required a lot of work,” Rattray said.
Perhaps that sophistication is what attracted big tech companies like OpenAI, Anthropic, and Meta, as well as Runway, Groq, Cerebras, Modern Treasury, and Cloudflare, to the stainless steel platform. Rattray claims that Stainless currently has “hundreds” of paying customers and that its SDK is downloaded tens of millions of times each week.
Most customers pay for the stainless steel enterprise tier, which comes with additional white glove services and AI-specific features. Publishing a single SDK is free. But companies must pay anywhere from $250 per month to $30,000 per year for multiple SDKs across multiple programming languages.
Rattray said the company's annual recurring revenue is hovering around $1 million, and Stainless is close to turning a profit. To grow, Stainless recently completed a $25 million Series A led by a16z with participation from Sequoia, The General Partnership, Felicis, Zapier, and MongoDB.
The total amount raised will be approximately $35 million, and Rattray said the new cash will be used to expand Stainless's 20-person team based in New York.
“While the business is very efficient, we have decided to raise funds to accelerate development towards our vision,” he added. “The SDK is just the first act. Our vision is to build a comprehensive platform that developers can use for everything API-related.”