Claude Fable 5 wrote a booting, NT-shaped Rust kernel in 38 minutes

[WhoCares]

Claude Fable 5 wrote a booting, NT-shaped Rust kernel in 38 minutes, with later work on Claude Opus growing it to run real Windows binaries.

Security startup Tolmo published a transcript-level account of Claude Fable 5 writing a booting, NT-shaped kernel in Rust from an empty directory in 38 minutes of active model work.

By the company's account it built the trusted computing base, booted in an emulator, passed its own self-tests, and root-caused its own low-level bugs, then over 8 more days, mostly on Claude Opus 4.8, grew to load unmodified Windows drivers and run real Windows binaries.

https://github.com/msuiche/nanokrnl

An NT-compatible kernel written in Rust: the architecture, abstractions, and (where it matters) the exact constants and layouts of the Windows NT kernel, rebuilt as a modern, memory-safe, freestanding Rust codebase. It boots on x86-64, runs real, unmodified Microsoft user binaries (cmd.exe, more.com, …) on its own NT syscalls, loads a genuine null.sys PE driver, and proves itself with a self-test suite on every boot.

It runs natively under QEMU and in your browser, via nanox, a bespoke ~60 KB x86-64 WebAssembly emulator that boots the unmodified kernel image directly in long mode, with no threads, no SharedArrayBuffer, and no COOP/COEP headers.

https://nanokrnl.ai