Practitioner (own blog/paper) New product / refactoring
An agent-written 150,000-line Rust app shows refactoring one 17,155-line file cut input tokens per change by 83%
Giles Edwards-Alexander built a work app of about 150,000 lines (≈120k Rust plus TypeScript and Terraform) written entirely by agents, mostly Claude Code with some Cursor, without reviewing the code. Its data access layer grew into a single 17,155-line Rust file. Over 15 refactoring steps he split it up and measured the same change each time: input tokens per change fell from 159,564 to 27,360.
The numbers (as reported)
| App size | ~150,000 lines (~120k Rust) |
|---|---|
| Largest file before | 17,155 lines |
| Largest file after | 3,695 lines |
| Input tokens per change | 159,564 → 27,360 (−83%) |
| Saving per change | ~39.7 cents at $3/MTok (author's estimate) |
Facts
- Company / subject
- Giles Edwards-Alexander (writing on martinfowler.com)
- Tools
- Claude Code, Cursor
- Codebase
- greenfield
- Work type
- New product / refactoring
- Stack
- Rust, TypeScript, Terraform, Firestore
- Published
- 2026-07-30
- Last checked
- 2026-10-19
Caveats
One app and one repeated change, measured by the builder. The author notes the dollar saving per change is small and the wider effect is unproven. Build time and total cost aren't given.