In this era of AI, the technology has rapidly touching its best way of evolving and reaching to the best mode ever.
Rewriting whole Bun tool which was released on May 2021 and entirely written on Zig which is a robust, effective and simpler alternative to C bit still quite powerful for developing such powerful tool Bun, which is ultimately becoming successor of Node and preferring by many now days.
The advantage of choosing Zig to develop Bun
The language does not have a hidden heap allocator or automatic garbage collection. Any function that needs to allocate memory must explicitly accept an allocator parameter, giving you total control over memory strategies
Origin and creation of Bun
It took Bun’s creator, Jarred Sumner, about 3 weeks to build the very first working prototype, and about 1 year to reach public beta. However, building a full-scale JavaScript runtime, package manager, and bundler from scratch is an incredibly massive undertaking. So, we can say that it took around 1 to 2 years to launch first successful public release of this tool.
Bun acquired by Anthropic
Bun was acquired by anthropic on December 2, 2025. It was acquired with purpose of something big in the vision of Anthropic.
Anthropic acquired Bun because its AI coding tool, Claude Code, relies heavily on the runtime, package manager, and bundler to compile and distribute its standalone executables to millions of users and Bun is best choice to utilize in that space and game changer for them.
The full article published by Anthropic about reason behind its acqiuisiton
A big shift and AI proved that it has crossed the humans perfection
This proves that how the software engineering become so advance and fast with launch of AI.
In July 2026, Bun creator Jarred Sumner announced that Bun was entirely rewritten from Zig to Rust. The migration of the ~535,000-line codebase took only 11 days and was completed using a fleet of 64 parallel Claude agents running via Claude Code. Below is the breakdown of key information.
Code Volume: ~500,000+ lines of Zig ported to Rust.
Timeframe: Completed in just 11 days.
Financial Cost: **Estimated $165,000 in Claude API usage.
**Token Volume: 5.9B uncached input tokens, 72B cached tokens, 690M output tokens.
Velocity: Reached a peak translation speed of 1,300 lines of code per minute.
Validation: Passed 100% of Bun's comprehensive, language-agnostic TypeScript test suite.
Why Leave Zig for Rust?
Sumner outlined several primary catalysts for abandoning Zig in favor of Rust:
Memory Safety & Stability: Bun struggled heavily with memory management bugs like use-after-free, double-free, and memory leaks. Moving to Rust provides compiler-enforced lifetime tracking and automated cleanup via RAII (Drop).
Contributor Accessibility: The Rust ecosystem is vastly larger than Zig's, making it easier to recruit contributors, secure community maintenance, and patch bugs at scale.
Anthropic Infrastructure Needs: Anthropic uses Bun heavily to power its terminal-based coding tool, Claude Code. Maintaining a stable, battle-hardened foundation became highly critical to corporate interests.
Reaction & Controversy
Andrew Kelley, the creator of Zig, publicly criticized the move. He attributed Bun's historical stability bugs to rushed engineering practices rather than flaws within Zig itself, asserting that translating half a million lines of code via LLMs results in unreviewed tech debt.
Critics and purists express severe discomfort over a core infrastructure tool being written by AI without exhaustive human review. Early automated pull requests to drop the Zig code were even flagged by automated systems as "AI slop".
A positive side of this transformation is showing that time and productivity for achieving or creating something big has become super fast and efficient in era of AI.
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