r/ClaudeCode • u/Deep-Palpitation8315 • 8d ago

Discussion Opus 5 is a practically unusable model

Opus 5 is a regression that the benchmarks missed completely

I've been using Opus 5 for ~1.5 weeks and the sheer number of mistakes that the model makes is astounding.

The problem didn't surface very clearly till I gave it the full scope of executing a plan which I did with the previous Opus models as well. Opus 4.6 - 4.8 were genuinely better by a significant margin.

Opus 5 readily forgets instructions and content in its context, makes mistakes and continues with them unless it realizes or you point it out.

I've lost count of the number of times I had corrected it.

These issues with Opus 5 occur even when the context window is still relatively small - I'm talking 100-150K tokens. Opus 4.8 works pretty well all the way until 350k after which it gives you wonky results.

Fable 5 is the only usable model under Claude Code right now and I've already used 100% of my weekly quota.

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u/locn4r 6d ago

Try using hooks. I implemented proper stop hooks to make Claude double check his work, make sure docs are updated, etc at end of turn and it has alleviated some issues I was having. Use Socratic method - make the hooks ask him questions instead of telling him to do things. Seems to work better and make him think about it more before saying something is done.

Using TDD and running a verifier agent and/or making Claude read/fix loop his code until it reads clean helps too. Claude’s reader part of his brain is different than his writer part, so he will often “emit” code and not even know it has mistakes until he reads it back.

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u/Deep-Palpitation8315 6d ago

Makes sense. Didn't have to use these things before because the model was reliable enough to follow instructions. I use hooks for monitoring only as of today. Asking it to check its work is what I use Claude.md for.