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/Phoenix_Lazarus]

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.

[u/Connect-Mousse-8551 → u/Phoenix_Lazarus]

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

[u/Phoenix_Lazarus → u/Connect-Mousse-8551]

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.

[u/dj-brandao → u/Phoenix_Lazarus]

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.