Earlier today I made Claude code implement a feature with fable. It worked roughly 60 minutes and used around 30% of my 100€ subs 5h sessions.

Then I typed /code-review in a second terminal/clean session after the analysis was done (no code changes) the usage was 99%. I then asked it to write that into a review.md so I could restart from that the next day. Sadly the last % wasn't enough for that.

Ymmv, these models behave very differently with no discernable reason. Usually reviews(even with fable) take like 10-20%... Yet suddenly you get it to burn through 65-69% in 15 minutes or so

/code-review in Claude Code spawns a lot of sub-agents (counted like 8 once), each looking at the code from some certain aspect (like correctness, maintainability, duplication, testing, etc). It eats tokens like crazy doing that, but also covers quite a lot. The default code review in Codex does far less (feels like it's only correctness) and doesn't uses subagents. Actually I made a skill for Codex that does a review closer to what Claude does by default, but using like 4-5 agents and some being cheaper models/less than xhigh reasoning. I'm getting pretty nice reviews with that that cover more than just correctness.