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fcoreutils: Claude Code autonomously rewrites GNU coreutils in Rust - up to 54x faster, 100% compatible.

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Core trick

SIMD-accelerated Rust rewrites of GNU coreutils tools, validated by an 826-case compatibility suite run in CI.

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dev tools

Description

fcoreutils: Claude Code autonomously rewrites GNU coreutils in Rust - up to 54x faster, 100% compatible. We gave Claude Code a small Linux machine with full sudo access, defined one goal (rewrite GNU coreutils with 100% compatibility and 10x-30x performance), and walked away. Zero human-written code. Claude Code consumed the full $500 API credit in 3 days + another 3 days Claude Max 20 - autonomously designing architecture, implementing 10 SIMD-accelerated tools, publishing 62+ releases to crates.io, and passing 826/826 compatibility tests. Results (independently verified via GitHub Actions): - wc: 54.3x faster than GNU, 28.6x faster than uutils/coreutils - sort: 18.1x faster than GNU, 15.1x faster than uutils - uniq: 13.4x faster than GNU - base64: 8.8x faster than GNU - cut/tr/tac: 5-7x faster than GNU Key: Claude Code didn't just match uutils/coreutils - it surpassed it across every tool. A single autonomous AI agent outperforming a major community-maintained Rust project.
AiBrush/coreutils-rs★ 30 forksRustMITCreated Feb 10, 2026 · last push Feb 23, 2026

README excerpt

<sub>🏆 Visiting from the **"Built with Opus 4.6: a Claude Code hackathon"**? See our [hackathon submission](Fcoreutils-hackathon-submission.md) for the full story.</sub>

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# fcoreutils

[![Test](https://github.com/AiBrush/coreutils-rs/actions/workflows/test.yml/badge.svg)](https://github.com/AiBrush/coreutils-rs/actions/workflows/test.yml)
[![Release](https://github.com/AiBrush/coreutils-rs/actions/workflows/release.yml/badge.svg)](https://github.com/AiBrush/coreutils-rs/actions/workflows/release.yml)
[![crates.io](https://img.shields.io/crates/v/fcoreutils?color=orange)](https://crates.io/crates/fcoreutils)
[![License: MIT](https://img.shields.io/badge/License-MIT-blue.svg)](LICENSE)
[![GitHub Release](https://img.shields.io/github/v/release/AiBrush/coreutils-rs)](https://github.com/AiBrush/coreutils-rs/releases)

High-performance GNU coreutils replacement in Rust — 10+ tools and counting. SIMD-accelerated, drop-in compatible, cross-platform.

## Performance ([independent benchmarks](https://github.com/AiBrush/coreutils-rs-independent-test) v0.7.1, Linux, hyperfine)

| Tool | Speedup vs GNU | Speedup vs uutils |
|------|---------------:|-------------------:|
| wc | **34.2x** | 18.8x |
| sort | **16.7x** | 15.4x |
| uniq | **15.8x** | 6.5x |
| base64 | **7.5x** | 6.9x |
| tr | **7.4x** | 7.3x |
| cut | **6.7x** | 3.7x |
| tac | **3.9x** | 1.9x |
| md5sum | **1.4x** | 1.3x |
| b2sum | **1.3x** | 1.1x |
| sha256sum | **1.0x** | 3.9x |

## Tools

### Performance-Optimized (10

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