Idiomatic Julia code in AI generated code

General Usage
7

Note “idiomatic” below, not in the paper, but what it enabled for Fortran porting:

.. Genesis used DeepSeek V4 Flash to build a Rust-based C compiler with about 250k tracked lines; the run lasted over 120 hours, archived over 1,000 agent episodes and incurred only US$44 in model-token charges. The compiler passed the complete c-testsuite and most LLVM and Csmith tests. In a separate compiler world generated with GLM 5.2, development continued after repeated agent replacement while retaining full test performance. Genesis also reimplemented 13 MESA modules with over 100k Fortran lines as a Rust workspace with nearly 90k Rust lines; across six numerical workloads, it achieved median speedups of 1.55–6.87x. These results show that long-horizon software development can be organized around a persistent project rather than a persistent agent. Project Website: this https URL

Costing US$10.64:

rewrite of the core numerical/physics stack of MESA — the original ~462K-LOC Fortran 90/2008 stellar astrophysics suite. This workspace ports the const → utils → math → mtx → interp_1d → interp_2d → num → chem → rates → neu → net → eos → kap module chain into 13 idiomatic Rust crates, mirroring the original module APIs to preserve backwards compatibility, and ships a benchmark harness that proves the port is faster than the original Fortran on every workload (medians of driver-internal timings, gfortran -O3 -march=native vs Rust release lto=fat, codegen-units=1).

Highlights

  • ~67K LOC of pure Rust library code (129 files, 13 crates), #![forbid(unsafe_code)] everywhere — zero unsafe, zero FFI.
  • ~1050 tests green (cargo test --workspace → 1052 passed / 0 failed / 18 ignored), including golden tests ported from the original Fortran test_output files (bit-exact or ~1e-9).
  • No LAPACK/BLAS FFI ..

Rest is older in chronological order:

So we are down 99% in cost since 6 months ago, then cost 444x making a C compiler (and now 2.8x quicker to make “120 hours”/5 days vs 2 weeks):

Over nearly 2,000 Claude Code sessions and $20,000 in API costs, the agent team produced a 100,000-line compiler that can build Linux 6.9 on x86, ARM, and RISC-V.

The key seems to be 1000/16 = 62x more agents, though only part of the reason, the paper is brand new to me.