Mitchell Hashimoto ships a non-trivial Ghostty feature with Amp in 16 sessions for $15.98
Mitchell Hashimoto built Ghostty's unobtrusive macOS update notifications largely with Amp and published all 16 agent sessions unedited. He planned first, used the agent to prototype SwiftUI, then ran repeated 'anti-slop' cleanup sessions. The agent failed on a titlebar bug across several attempts, so he changed the design; it also produced a backend he threw away before he restructured the view model by hand.
The numbers (as reported)
| Agent sessions | 16 |
|---|---|
| Token spend | $15.98 |
| Hands-on time (author's estimate) | ~8 hours, over 3 days from first to last commit |
Facts
- Company / subject
- Ghostty (Mitchell Hashimoto)
- Tools
- Amp
- Codebase
- brownfield
- Work type
- Feature
- Stack
- Swift, SwiftUI, macOS
- Published
- 2025-10-11
- Last checked
- 2026-10-18
Caveats
A lot of human coding too: he edited after almost every session and did a final manual review before merging. The agent couldn't fix the key titlebar bug (he pivoted to an overlay), and its first backend was 'obviously the wrong approach' and thrown away. He thinks it was faster than doing it alone, but no estimate was made in advance. The author says he has no financial ties to any AI company.