How Stainless Is Automating Software Libraries for AI and Fintech Companies
Stainless, a New York startup founded in early 2022, has raised $25 million in Series A funding to scale its platform for automatically generating software libraries—known as SDKs, or software development kits. The company helps API-first companies (those built primarily around web-based interfaces that other software can plug into) avoid the expensive work of maintaining libraries for multiple programming languages.
Stainless already generates libraries for major platforms including OpenAI, Anthropic, Runway, and Meta's Llama Stack in the AI space, alongside fintech infrastructure firms like Metronome and Modern Treasury, and developer platforms such as Cloudflare and Mux.
Why SDK Maintenance Is Such a Burden
Imagine an API company—say, OpenAI—wants developers using Python, JavaScript, Java, Go, and Rust to integrate its services. Without automation, the company has to maintain a separate library for each language, with a team keeping each one up to date as the API changes. That's expensive and time-consuming.
Beyond cost, manual maintenance creates hidden problems. One language's library might implement a feature differently than another. Documentation can fall out of sync. New API features roll out unevenly across languages, frustrating developers using less-favored languages.
Stainless solves this by automatically generating these libraries from a single source description of the API—a specification that defines what the API does and how it works. The generator then creates idiomatic code (code that follows each language's natural conventions) for each target language, so Python libraries look like Python, Go libraries look like Go, and so on.
The Clients Tell the Story
The breadth of Stainless's customer base shows where API-first infrastructure has taken hold. In AI, every major platform is a client. In fintech, payment and billing infrastructure companies have shifted entirely to API-first models—developers integrate programmatically rather than through manual setup. And in developer platforms like Cloudflare and Mux, SDK quality directly shapes whether a developer chooses to use the service.
This reflects a shift that has been underway since the early 2010s: enterprise software is increasingly built around APIs rather than packaged applications you install. As that transition has matured, companies have come to see SDK quality as a competitive advantage. If your library is clunky or slow to get new features, developers will choose a competitor.
Why This Matters Now
Three things have converged to make Stainless's timing significant. First, the explosion of AI APIs means developers are often juggling integrations with multiple services in a single application—so they need high-quality, consistent libraries from each platform. Second, fintech infrastructure has stabilized around API-first providers, making seamless integration critical. Third, as developer platform companies compete harder for attention, SDK quality has become a way to stand out.
Raising $25 million for a developer tools company in a selective investment climate signals that investors see real demand here.
What Automated Generation Actually Involves
It sounds simple—"just generate code from a spec"—but it's genuinely complex work. The system has to understand different API specification formats, translate data types correctly across languages (a string in one language isn't the same as a string in another), and generate code that feels natural to each language's developers. It has to handle authentication, error handling, and documentation generation. And it has to let the API evolve without breaking code that developers have already written.
Mainstream, Not Early-Stage
One striking fact: major platforms like OpenAI and Cloudflare—companies with huge developer bases and plenty of engineering resources—trust automated SDK generation for critical infrastructure. That's not how early-stage technology usually works. Early adopters experiment; mainstream companies adopt only when the approach has proven itself.
The client list suggests automated SDK generation has crossed that threshold. These companies wouldn't stake their developer experience on automation if it weren't working.
For API-first companies deciding whether to build or buy SDK maintenance tools, the economics become clearer at scale. If you support five languages and release new API features monthly, automation saves money and headaches. And as more companies adopt API-first models, that pressure only increases.
The broader pattern here is one I've watched repeat across technology waves: as infrastructure matures, companies stop building commodity pieces themselves and instead buy specialized tools. Stainless is riding that wave.
