Acquisition
<cite index="3-3,3-4">Anthropic on May 18, 2026 announced it had acquired Stainless, describing the New York–based company as a leader in SDK (Software Development Kit) and MCP (Model Context Protocol) server tooling.</cite> <cite index="3-5,3-6,3-7">Founded in 2022, Stainless has powered the generation of every official Anthropic SDK since the earliest days of the Claude API (Application Programming Interface), and converts API specifications into SDKs across TypeScript, Python, Go, Java and other languages.</cite>
Financial terms were not disclosed. <cite index="1-4">The Information had reported the week prior that Anthropic was in talks to acquire Stainless — backed by Sequoia Capital and Andreessen Horowitz — for more than $300 million.</cite> <cite index="9-12">Stainless was founded by Alex Rattray, who previously built Stripe's API client library code generation system.</cite>
<cite index="1-6,1-7">Anthropic said it will wind down all hosted Stainless products, including the SDK generator, though existing customers will retain ownership of the SDKs they have generated and full rights to modify and extend them.</cite> <cite index="7-22,7-23">Stainless had also sold software to rival model providers including OpenAI and Google, meaning Anthropic is absorbing infrastructure that previously supported competing ecosystems.</cite>
In the announcement, <cite index="4-6,4-7,4-8">Katelyn Lesse, Head of Platform Engineering at Anthropic, said "Stainless has shaped how developers experience the Claude API since the start" and that agents are only as useful as what they can connect to.</cite>
Strategic context
The deal is Anthropic's fourth in roughly six months. <cite index="9-25,9-26,9-27,9-28,9-29">Prior acquisitions include Bun, a JavaScript runtime, in December 2025; Vercept, an AI computer-use startup, in February 2026; and Coefficient Bio, a stealth biotech startup, in April 2026 for just over $400 million in stock.</cite> Each transaction targets a distinct layer of an emerging agent stack: runtime, autonomous operator, vertical application, and now developer connectivity.
MCP, the open protocol Anthropic authored, has become a de facto standard for connecting LLM (Large Language Model) agents to external tools. <cite index="5-8">By March 2026, MCP had crossed 97 million monthly SDK downloads, supported more than 10,000 public servers, and gained formal adoption from major AI providers including OpenAI, Google DeepMind, Microsoft and AWS.</cite>
Financing backdrop
The acquisition lands amid one of the largest private fundraises in technology history. <cite index="11-2,11-3">Anthropic is in talks with investors about raising cash at a valuation of $900 billion, a level that would push it past OpenAI, which was most recently valued at just over $850 billion.</cite> <cite index="16-1,16-2,16-3,16-4">According to Bloomberg, Anthropic is seeking to raise at least $30 billion in what would be its largest financing to date, with discussions centered on a pre-money valuation exceeding $900 billion, though no formal term sheets have been signed.</cite>
<cite index="10-4,10-8,10-9,10-10">TechCrunch reported the round is expected to be roughly $50 billion and is likely to be Anthropic's last private round before going public, with some early backers skipping the round to potentially cash out during an anticipated IPO later this year.</cite> <cite index="14-7,14-8">The company is exploring a potential initial public offering as early as October, with the capital viewed as essential for securing computing power to sustain growth.</cite>
The fundraise follows reported revenue acceleration. <cite index="11-4,11-22,11-23">Anthropic said earlier in the month that its business reached $30 billion in annualized revenue, after generating roughly $10 billion in revenue last year.</cite> <cite index="11-18,11-19,11-20">The company has also secured up to 5 gigawatts of compute capacity via Amazon and a further 5 gigawatts through an arrangement with Google and Broadcom, while Google has said it plans to invest up to $40 billion in Anthropic.</cite>