The archive · Developer & Business Tools · Strategic decision · 2022–2026
Stainless' $35M neutral SDK bet: Anthropic's $300M+ buyout wound down products
NYC SDK generator used by OpenAI, Anthropic, Google and Cloudflare raised ~$35M, hit ~$1M ARR, then sold for $300M+ as hosted products wound down.
Stainless
What the business is
Stainless sold a hosted platform that compiled API specifications into production-ready, multi-language SDKs (Python, TypeScript, Kotlin, Go, Java), CLIs and MCP servers, and kept them updated automatically as APIs evolved.
Starting capital：~$35M total per TechCrunch: a $3.5M seed with Sequoia and The General Partnership (reported Apr 2024) and a Dec 2024 $25M Series A led by a16z with Sequoia, The General Partnership, Felicis, Zapier and MongoDB Ventures; ~$1M ARR and near-profitability claimed at the Series A.
How it started
Alex Rattray, an economics major who learned to code at UPenn, joined Stripe's developer platform team, where he helped revamp API docs and launch the system powering Stripe's API client SDKs. Seeing that handwriting SDKs couldn't scale, he founded Stainless in New York in 2022, bootstrapping 'with revenue from day one.'
What happened
By April 2024 Stainless had 'dozens' of paying beta clients — OpenAI, Anthropic, Together AI, Lithic, LangChain, Orb, Modern Treasury and Cloudflare — and closed a $3.5M seed with Sequoia and The General Partnership. In December 2024 it raised a $25M Series A led by a16z (total ~$35M), claiming hundreds of customers and tens of millions of weekly downloads, with ~$1M ARR and near-profitability; the 20-person NYC team planned to build 'the comprehensive platform developers turn to for everything API-related.'
How it ended up
On May 18, 2026 Anthropic announced the acquisition of Stainless; The Information had reported talks at over $300M. Anthropic told TechCrunch it would wind down all hosted Stainless products, including the SDK generator: new signups stopped immediately, existing customers keep full rights to SDKs already generated, and the team moved into Anthropic's Claude Platform group.
Background
Stainless was founded in 2022 in New York by Alex Rattray, a former Stripe engineer who had helped build the system behind Stripe's API client SDKs. His product took an API specification and compiled it into production-ready SDKs in Python, TypeScript, Kotlin, Go and Java, then kept them updated as the API changed, replacing the teams of engineers vendors previously needed just to maintain libraries.
The bet was that one neutral vendor could serve every major AI lab at once. Customers included OpenAI, Anthropic, Google, Meta, Cloudflare, Runway, Modern Treasury and Orb; by December 2024 Rattray claimed hundreds of paying customers and tens of millions of weekly SDK downloads, with annual recurring revenue around $1 million and the company nearing profitability (TechCrunch).
Stainless raised a $3.5M seed with Sequoia and The General Partnership (reported April 2024) and a $25M Series A led by a16z in December 2024, bringing total funding to about $35M. Traction was visible on Hacker News: the April 2024 launch post drew 216 points, and the May 2026 acquisition story drew 531 points and 382 comments.
On May 18, 2026 Anthropic announced it had acquired Stainless; The Information reported the price above $300M. Anthropic told TechCrunch it would wind down all hosted Stainless products, including the SDK generator — new signups stopped that day, customers kept ownership of generated SDKs, and the team folded into Anthropic's Claude Platform team.
What has to be true
- Serving every major AI lab made Stainless a strategic prize: the $300M+ deal cut OpenAI, Google and Cloudflare off from SDK tooling they relied on (TechCrunch).
- The hosted-product bet was fragile by design: as neutral infrastructure, its fate depended on the strategy of the biggest customer, and Anthropic's internalization ended the standalone business.
- Growth stayed modest relative to the price: ~$1M ARR against a reported $300M+ valuation meant the exit value was strategic, not a multiple on revenue (TechCrunch Dec 2024).
- The wind-down was abrupt: new signups, projects and SDKs stopped immediately, showing how fast a neutral devtools platform disappears when an acquirer wants the team, not the product.
What can be applied
Serving rival AI labs made Stainless a prize, not a moat: the $300M+ acquisition that paid off founders and investors also killed the neutral hosted product.
Aftermath
As of 2026-09-02, Stainless's hosted products — the SDK generator, MCP tooling and hosted releases — are wound down: Anthropic said new signups, projects and SDKs stopped immediately, while existing customers keep full ownership of generated SDKs and were pointed to transition tooling. The Stainless team joined Anthropic's work on Claude Platform and agent connectivity. The deal also removed the SDK infrastructure that OpenAI, Google, Cloudflare, Replicate and Runway had relied on, leaving competitors to run their own tooling or switch to rivals such as Speakeasy and LibLab.
Sources
- Anthropic has acquired the dev tools startup used by OpenAI, Google, and Cloudflare
- Anthropic acquires Stainless
- Anthropic acquires Stainless (Hacker News thread)
- Stainless helps build SDKs for OpenAI, Anthropic, and Meta
- Stainless is helping OpenAI, Anthropic and others build SDKs for their APIs
- The Stainless SDK Generator (Hacker News thread)
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