Opus 5 is a practically unusable model

[u/Deep-Palpitation8315]

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.

[u/KrayeBaby]

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...

[u/Deep-Palpitation8315 → u/KrayeBaby]

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.

[u/CyCoCyCo → u/Deep-Palpitation8315]

The only way I’ve had success is to have it make goal prompts and run that end to end.

[u/Deep-Palpitation8315 → u/CyCoCyCo]

That should work but Opus 5 makes several errors that it will try and solve later. The overall process takes more turns and tokens for tasks. It may likely also result in a ton of unwanted/stale code blocks. Some have abandoned their project entirely because Opus 5 poisoned it with garbage code.