Anthropic acquired Bun, the fast JavaScript runtime, on December 2, 2025—marking the AI company’s first-ever acquisition. The timing is no coincidence. Claude Code just hit $1 billion in run-rate revenue, only six months after launching publicly. While GitHub Copilot took years to build a $2 billion business with 20 million users, Anthropic reached $1 billion in half a year. The AI coding market is no longer hype—it’s a $3.1 billion category racing toward $24-65 billion by 2030. Anthropic isn’t just competing on model quality anymore. They’re buying infrastructure.
Why Anthropic Bought Bun
Anthropic Chief Product Officer Mike Krieger explained the acquisition succinctly: “Bun represents exactly the kind of technical excellence we want to bring into Anthropic.” That’s the diplomatic answer. The strategic reality is sharper: Anthropic wants to own the entire AI coding stack—from runtime to package manager to agent. Bun gives them that foundation.
Bun isn’t just another JavaScript runtime. It’s 3-4x faster than Node.js in HTTP server benchmarks, hitting 120,000 requests per second compared to Node.js’s 32,000. Cold starts take 8 milliseconds versus Node.js’s 42 milliseconds. For AI coding agents that execute thousands of code snippets daily, those performance gains compound. Speed isn’t a luxury—it’s infrastructure.
The acquisition mirrors Microsoft’s playbook. Microsoft owns GitHub, VS Code, and GitHub Copilot—controlling the entire developer workflow. Anthropic is doing the same: Bun powers Claude Code, which runs on Anthropic’s models. Vertical integration isn’t new, but in AI coding, it’s becoming the only strategy that scales.
Hacker News users speculated that Anthropic needed “a fast and sandboxed code executor” for autonomous agents. They’re right. AI agents don’t just suggest code—they run it, test it, and iterate. Sandboxed execution environments need to be fast, secure, and reliable. Bun checks all three boxes.
What Is Bun and Why Does It Matter
Bun is a JavaScript runtime built with Zig and powered by WebKit’s JavaScriptCore engine instead of V8. It’s not just a runtime—it’s an all-in-one toolkit combining a package manager, bundler, and test runner. That consolidation matters. Developers aren’t juggling npm, Webpack, and Jest anymore. Bun handles it natively.
Adoption metrics show momentum: 7 million monthly downloads, 70,000 GitHub stars, and 32% of new JavaScript projects evaluating it. Companies like Midjourney, Shopify, and Vercel use Bun in production. Vercel officially supports Bun Runtime for serverless functions. For a project launched in 2022, that’s rapid penetration.
Bun will remain open source under the MIT license, Anthropic promises. That’s the right move—killing the open source license would torch developer trust overnight. The real question isn’t the license. It’s the roadmap. Will Bun optimize for Claude Code’s AI agent use cases or for the broader JavaScript ecosystem? Can it stay neutral when Anthropic owns both the tool and the infrastructure it runs on?
Open Source Under Corporate Control
Anthropic’s promise to keep Bun open source is necessary but not sufficient. Microsoft owns GitHub and VS Code, and developers mostly trust them—mostly. Elastic battled AWS over monetizing open source infrastructure, spawning forks and fracturing communities. Redis Labs, MongoDB, and Confluent all changed licenses to prevent cloud providers from profiting off their work without contributing back.
The pattern is consistent: corporate ownership of critical open source infrastructure creates tension. Anthropic might have the best intentions, but incentives matter. If Claude Code needs a feature that benefits AI agents but complicates general JavaScript development, which takes priority? The answer determines whether Bun stays community-driven or becomes Anthropic-first.
Competing AI coding tools face a choice now. GitHub Copilot runs on Microsoft’s infrastructure. Cursor is independent but relies on third-party runtimes. If Anthropic optimizes Bun exclusively for Claude Code, competitors may build or acquire their own runtimes. Fragmentation hurts everyone.
Market Implications
The AI coding tools market generated $3.1 billion in revenue in 2025, up from effectively zero in 2021. GitHub Copilot leads with $2 billion in annual recurring revenue, 20 million users, and 82% enterprise adoption. Cursor exploded from $200 million to $500 million in ARR within months, with valuation talks jumping from $400 million to $10 billion in under a year. Claude Code hit $1 billion ARR in six months—the fastest ramp in Anthropic’s history.
The numbers validate the market, but they also reveal the new battlefield: infrastructure. GitHub Copilot benefits from Microsoft owning GitHub and VS Code. Cursor differentiates on developer experience but lacks infrastructure control. Anthropic now owns Bun, giving Claude Code a performance edge competitors can’t easily replicate.
This is the first infrastructure acquisition in the AI coding wars. It won’t be the last. Expect GitHub, Cursor, or new entrants to build or buy runtimes, bundlers, or package managers. Vertical integration isn’t optional anymore—it’s the cost of competing.
Key Takeaways
- Anthropic acquired Bun on December 2, 2025, marking its first acquisition as Claude Code hit $1 billion in run-rate revenue just six months after launch
- Bun is 3-4x faster than Node.js and provides infrastructure for AI agents to execute code securely and efficiently at scale
- Anthropic mirrors Microsoft’s vertical integration strategy—owning the runtime (Bun) powers its AI tool (Claude Code) just as Microsoft controls GitHub, VS Code, and GitHub Copilot
- Bun remains MIT-licensed, but corporate ownership raises questions about roadmap priorities: AI-first features versus broader JavaScript ecosystem needs
- The AI coding market grew from zero to $3.1 billion in four years and is projected to reach $24-65 billion by 2030, with infrastructure control emerging as the new competitive moat
