Claude Code bug can silently 10-20x API costs

But this was a lot of work. Analyzing thousands of files and extracting data from them using headless Claude sessions with a concurrency of 20 sessions at once. I have no complaints from those two days.

Then yesterday (day 3 of the week) I did some minor refactoring and bug fixes for 2 or 3 hours. Somehow that took me from 50% to 90%. This morning I finished off some of the bug fixes, maybe 45 minutes of work across ~4 twenty minutes sessions, each of involved identifying the test gap, then using a single subagent to fix it with TDD.

That took me to 100%.

Also, I'm on Asia time so I'm working entirely during off peak hours.

I now have two days to wait before the session rollover and I'm feeling quite frustrated. Whether it's a bug or they just silently reduced session limits, it's not acceptable for $200 a month.

((Is there any way to audit this aside from reverse engineering? You get less than you pay for?))

I've recently had the displeasure of Opus 4.6 hallucinating an API. It would have been great if that API had existed, but it did not. Still, it then looped until I manually terminated it while trying to make tests pass. In my case, I used up about $12 of usage in 30 minutes. My guess would be mostly through the (pretty verbose) thinking tokens.

But it's not just Anthropic. I had the same issue with Gemini 3.1 Pro.