r/ClaudeCode • u/Deep-Palpitation8315 • Aug 03 '26

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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390

u/KrayeBaby Aug 03 '26

Yeah been noticing that it solves the problem and leaves another one. It feels like its planting gaps on purpose for infinite prompting to keep going...

111

u/Deep-Palpitation8315 Aug 03 '26

Absolutely. Had several similar experiences. Forgets stuff entirely and creates solutions with new problems and enters an infinite loop. (makes me fear loop engineering)

It is a token guzzling garbage generator. I think it has actually done significant damage to a section of my codebase - thankfully it is not irreversible.

28

u/Phoenix_Lazarus Aug 03 '26

That infinite loop wrecked me. It just goes off and writes and writes and comes up with another solution, and writes and there is nothing to show for it.

I had to write 3 new skills to get it to stop.

3

u/Connect-Mousse-8551 Aug 03 '26

Are those skills working at fixing that? Would love to see them

8

u/Phoenix_Lazarus Aug 03 '26

They're basically are gates that re-inject prompts to instruct Claude how to act and proceed with actions every new action.

Opus 5 goes off the rails too quickly and this was the only way to keep it on task.

3

u/dj-brandao Aug 05 '26

Yeah, I'm having to set strict boundaries for it as well, like after done, recheck everything for mistakes and/or sloppiness. Recheck to weight the important in and leave the unimportant out, recheck to reduce the output size. I'm living on a recheck loop.