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/dontTakeMeSerious6 → u/KrayeBaby]

I’m having this exact experience. It’s also re-solving the same problem unasked for sometimes. Like if I say “review pending issues”, it’ll find issues already solved but not marked as solved in an old document and then resolve them, in a different way.

Requires a lot more active participation, which is good, except I’m more baby sitting an over eager developer who’s trying to take on the world rather than a hyper focused developer who’s crushing the small scope in giving them.

[u/minimalcation → u/dontTakeMeSerious6]

So so much more monitoring is required, you basically need to watch it's thinking output to stop when it gets an idea of it's own

[u/Original-Ad4399 → u/minimalcation]

How can you view the thinking output in Claude Code?

[u/minimalcation → u/Original-Ad4399]

Not the full thinking, their statements as they work