Stainless Secures $25M Series A Funding to Revolutionize API Integration with AI-Generated SDKs

Stainless Secures $25 Mn Series A Funding for API Integration

Stainless, founded in 2022, streamlines API development with its SDK generator. NYC-based Stainless, a tech startup focused on API integration, has raised $25 million in Series A funding. The round was led by a16z, with support from Sequoia, The General Partnership, and others like Felicis, Zapier, and MongoDB Ventures. The funding highlights the rising demand for strong API tools. With the new funding, Stainless plans to expand its team and further enhance its platform, addressing rising developer expectations and the evolving role of APIs in agentic AI. The company's vision is to become the go-to solution for all API-related development. Founded in 2022, Stainless aims to simplify how developers work with APIs through its Stainless SDK generator. It creates high-quality, multi-language SDKs tailored to developers' needs, making API integration simple across industries. "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," said Alex Rattray, founder at Stainless. The company's auto-generated SDKs let customers focus on building great APIs. Stainless powers SDKs for leading AI platforms like OpenAI, Anthropic, and Meta, as well as fintech companies such as Modern Treasury and Orb. Developer-focused platforms like Cloudflare and Mux also rely on Stainless, which handles complex tasks like auto-pagination, retries, and version management. The rise of AI has made this even more critical. With AI agents performing thousands of API calls based on specifications and documentation, there's minimal tolerance for poorly designed SDKs. A bad SDK can disrupt agent workflows, explained Jennifer Li, lead partner at a16z.

Stainless Software gets $25M in funding to bring AI-generated SDKs to developers - SiliconANGLE

Stainless Software gets $25M in funding to bring AI-generated SDKs to developers Stainless Software Inc., which uses artificial intelligence to help companies quickly create software development kits for their applications and services, said today it has raised $25 million in a Series A round of funding. Today's round was led by a16z and saw participation from existing investors such as Sequoia and The General Partnership, as well as previous backers including Felicis, Zapier, MongoDB Ventures and angel investors like the former Stripe Inc. Chief Operating Officer Claire Johnson and Datadog Inc. President Amit Agarwal. The startup has created a tool that relies on an AI-powered compiler to automatically generate SDKs from application programming interfaces, with minimal input from developers. The Stainless SDK generator has already proven useful to thousands of developers, who expect technology companies to provide them with SDKs along with their products, so they can create applications that leverage those products more easily. But those developers don't always get what they want, as many companies will only provide an API, which is a protocol that allows software components to interact with each other. While APIs have emerged to rule the world as the foundation of almost every kind of modern application, SDKs are not nearly as common. That's because creating them is a massive challenge, and many companies don't have the necessary skills and expertise on hand to overcome it. In a blog post, Stainless founder and Chief Executive Alex Rattray said that, with an SDK, developers are basically getting a blueprint for building an application. But the lack of an SDK forces API users to read through massive volumes of documentation and build everything from scratch. So what's needed is a way to make it simple for every company to provide an SDK with their APIs. In an age where AI is already able to automate the creation of entire applications and codebases, it makes sense that AI should also be able to quickly slap together a usable SDK, and that's what Stainless is all about. Its Stainless SDK generator works by digesting an APIs specifications and churning out an SDK that can support various programming languages, including Python, Kotlin, TypeScript and Go. And as the API evolves over time, Stainless can push those updates into its SDKs, adapting them to fit. Stainless's AI algorithms get started by generating an initial configuration for the SDK, and developers will then be able to fine-tune it as needed. In doing this, Stainless avoids problems with inconsistent or outdated libraries. "Using Stainless, companies can build a world-class API DX without dedicating full-time engineers to SDK maintenance," Rattray said. "Their SDKs are consistent across languages, up-to-date, and easy for developers to use, even with rapidly changing APIs." Stainless isn't an entirely original idea, as startups like LibLab Inc. and Speakeasy Inc. also offer SDK generators for APIs, and there are open-source variants too, such as the OpenAPI Generator project. However, Rattray believes that Stainless sets itself apart from those rivals with its compiler, which creates much more "polished" code. The proof is in the pudding, and a lot of leading AI companies have opted to use Stainless instead of those alternatives. The startup says its customers include the likes of OpenAI, Anthropic PBC, Meta Platforms Inc., Runway AI Inc., Cerebras Systems Inc. and Cloudflare Inc. Rattray claims to have hundreds of paying customers and says that "millions of AI developers" download its SDKs every single week. The company provides access to its SDK generator in several tiers, including a free version that allows users to publish a single SDK. But to generate and publish multiple SDKs in several different programming languages, companies are required to pay anything from $250 per month to $30,000 a year. Stainless' business model appears to be working, for Rattrat told TechCrunch that the company has amassed around $1 million in annual recurring revenue, making it almost profitable. Rattray believes his company has an extremely bright future, as he expects the role of APIs to become even more important with the rising adoption of AI. After all, APIs are essential components of the data pipelines that feed every AI application. "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," he said.

Stainless helps build SDKs for OpenAI, Anthropic, and Meta

Devs expect tech vendors to supply software development kits, or SDKs, alongside their products to make it easier to create apps using those products. But many vendors only offer APIs, which are simply protocols that enable software components to communicate with each other. Alex Rattray, the founder of Stainless, thinks AI can assist, here. Stainless uses AI to generate SDKs from APIs automatically, largely on the fly. As Rattray explained to TechCrunch, without an SDK, API users are forced to read API docs and build everything themselves. Yet there isn't an easy way for vendors to create SDKs for their APIs at scale. Stainless takes in an API spec and generates SDKs in a range of programming languages including Python, TypeScript, Kotlin, and Go. As APIs evolve and change, Stainless' platform pushes those updates with options for versioning and publishing changelogs. While a typical vendor might have in-house devs building libraries in various languages to connect to their API, Stainless uses AI to produce an initial config, which teams can then fine-tune to their API. Rattray asserts that this avoids problems like libraries becoming inconsistent or outdated, and can drive quicker upgrades and faster time to integration. "We're quickly entering a world where everyone has access to an expert-level engineer in their pocket," he said. "With that shift, every company with a website will see their APIs grow from a power-user feature to a primary interface for all users, and companies without excellent APIs will become as anachronistic as a restaurant without a website." Much of Stainless' functionality was informed by Rattray's experiences in the industry. Rattray, an economics major, 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 to revamp API documentation and launch the system that powers Stripe's API client SDK. Stainless isn't the only API-to-SDK generator out there. There's LibLab and Speakeasy, to name a couple, plus longstanding open source projects such as the OpenAPI Generator. But Rattray argues that Stainless delivers more "polish" thanks to AI. "While the OpenAPI Generator exists, many customers mention having tried it," Rattray said, "and it having fallen extremely short on code quality in its outputs -- often requiring much more work to edit the output and bring it up to snuff." It's perhaps that polish that attracted tech giants like OpenAI, Anthropic, and Meta to Stainless' platform, as well as Runway, Groq, Cerebras, Modern Treasury, and Cloudflare. Rattray claims that Stainless has "hundreds" of paying customers today, and that its SDKs are being downloaded tens of millions of times every week. Most customers are paying for Stainless' enterprise tier, which comes with additional white-glove services and AI-specific functionality. Publishing a single SDK is free. But companies have to fork over between $250 a month and $30,000 a year for multiple SDKs spanning multiple programming languages. Rattray says that the company's annual recurring revenue is hovering around $1 million, and that Stainless is nearing profitability. To grow, Stainless recently closed a $25 million Series A led by a16z with participation from Sequoia, The General Partnership, Felicis, Zapier, and MongoDB. Bringing its total raised to ~$35 million, the new cash will go toward expanding New York-based Stainless' 20-person team, Rattray said. "The business is very efficient, but we decided to raise to accelerate development toward our vision," he added. "SDKs are just the first act -- our vision is to build the comprehensive platform developers turn to for everything API-related."