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Anthropic buys Stainless, the SDK toolmaker shared by OpenAI and Google

Anthropic buys Stainless, the SDK toolmaker shared by OpenAI and Google

Money Moves

$300M+ deal pulls a piece of shared AI infrastructure out of competitors' hands

May 19th, 2026: Anthropic publicly announces acquisition

Overview

For years, the developer kits that let outside engineers plug into OpenAI, Google, Meta and Cloudflare were generated by the same outside vendor: a New York startup called Stainless. Anthropic bought it this week for more than $300 million and said it will shut the shared service down.

The deal pulls a piece of common AI plumbing into one lab's hands. It is Anthropic's fourth acquisition in six months. AI labs are now absorbing the tools that connect their models to outside software rather than sharing them.

Why it matters

If you build on OpenAI or Google's APIs, the team that quietly maintained your client library now works for their biggest competitor.

Questions about this story

0

List the recent purchase they have made and what they hoped to buy with each purchase.

Anthropic made four acquisitions in six months — Bun, Vercept, Coefficient Bio, and Stainless — each targeting a different layer of the software stack Claude needs to act in the wider world.

Why it matters: The buying spree is a bet that owning the infrastructure layer — from JavaScript runtimes to SDK generators — gives Claude a structural edge that model quality alone can't deliver.

  • Bun (Dec 2025, undisclosed price): the fast JavaScript runtime — Anthropic wanted the developer-side execution layer for AI coding agents.
  • Vercept (Feb 2026, undisclosed price): an AI computer-use startup — Anthropic wanted to give Claude the ability to see and operate desktop software, not just generate text.
  • Coefficient Bio (Apr 2026, ~$400M in stock): a stealth biotech AI startup backed by Dimension — Anthropic wanted former Genentech researchers and drug-discovery capability to anchor a life sciences vertical.
  • Stainless (May 2026, $300M+): the SDK generator used by OpenAI, Google, Meta, and Cloudflare — Anthropic wanted the tooling layer that connects any AI model to outside software, and is shutting the shared service down.
Room for disagreement
  • The Stainless shutdown is contested in the developer community: critics argue Anthropic is deliberately degrading a neutral tool to handicap OpenAI and Google, while Anthropic frames it as consolidating developer tooling around Claude — the same facts, opposite interpretations of intent.
AI-generated with web search — may be wrong. Check the linked sources.

Key Indicators

$300M+
Reported deal price
Anthropic paid over $300 million, roughly double Stainless's December 2024 valuation.
4
Anthropic acquisitions in 6 months
Bun, Vercept, Coefficient Bio and Stainless, since December 2025.
6
AI labs that used Stainless SDKs
Anthropic, OpenAI, Google, Meta, Cloudflare and Runway all relied on its generator.
$150M
Stainless valuation 5 months earlier
Set by a $25M Series A led by Andreessen Horowitz in December 2024.

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People Involved

Organizations Involved

Timeline

January 2021 May 2026

8 events Latest: May 19th, 2026 · 1 month ago
Tap a bar to jump to that date
  1. Anthropic publicly announces acquisition

    Latest Announcement

    Anthropic posts the deal on its newsroom and says the Stainless team will focus on connecting Claude to outside data and tools.

  2. Deal confirmed to TechCrunch

    Acquisition

    Anthropic confirms the purchase to TechCrunch and says it will wind down all hosted Stainless products, including the SDK generator.

  3. The Information reports talks

    Reporting

    The Information reports Anthropic is in advanced talks to acquire Stainless for more than $300M, roughly double its prior valuation.

  4. Anthropic acquires Coefficient Bio

    Acquisition

    Anthropic pays roughly $400M in stock for the stealth biotech AI startup, adding former Genentech researchers to its life sciences group.

  5. Anthropic acquires Vercept

    Acquisition

    Anthropic absorbs Vercept, an AI computer-use startup, to push Claude's ability to operate desktop software.

  6. Anthropic acquires Bun

    Acquisition

    Anthropic buys the maker of the Bun JavaScript runtime, the first in what becomes a six-month string of developer-stack deals.

  7. Stainless raises $25M Series A

    Funding

    Andreessen Horowitz leads a $25M round at a $150M valuation. By this point, Stainless is generating SDKs for OpenAI, Anthropic, Google and Meta.

  8. Stainless founded

    Founding

    Alex Rattray, a former Stripe developer-platform engineer, starts Stainless to auto-generate client SDKs from API specifications.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

June 2018

Microsoft acquires GitHub (2018)

Microsoft paid $7.5 billion in stock for GitHub, the code-hosting service then used by tens of millions of developers including engineers at Amazon, Google and Apple. Rivals worried Microsoft would degrade the service or mine private repositories for competitive intelligence. Microsoft kept GitHub independent under CEO Nat Friedman.

Then

Most users stayed. Some moved private code to GitLab or Bitbucket, but GitHub's developer base kept growing past 100 million accounts.

Now

GitHub became the launchpad for Microsoft's AI coding push, including GitHub Copilot. Microsoft used its developer mindshare to seed AI-coding distribution, which now shapes the same lab-controlled tool stack Anthropic is buying into.

Why this matters now

A large platform bought the developer infrastructure its rivals depended on. The 2018 deal showed an acquisition can quietly tilt a developer ecosystem toward the new owner, even without obvious lockouts.

April 2009 to January 2010

Oracle acquires Sun Microsystems and MySQL (2010)

Oracle paid $7.4 billion for Sun Microsystems, which owned MySQL, the open-source database powering most of the web at the time. Database competitors and the European Commission worried Oracle would starve MySQL to protect its own paid database. Oracle promised to keep developing it.

Then

MySQL's original creator, Michael Widenius, forked the project into MariaDB within months. Wikipedia, Google and others moved to MariaDB over the next few years.

Now

MySQL is still maintained but lost its position as the default open database. The episode became a standard reference point for why depending on infrastructure owned by a competitor is risky.

Why this matters now

Like Stainless, MySQL was shared plumbing used by rivals. Oracle's deal shows how an acquisition can drain trust from a tool even when the buyer keeps developing it, pushing competitors to fork or rebuild.

Sources

(9)