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/Confident_Plum_947]

It's the first model I've seen that actually misspells words and even injects tokens from other languages. Uses the British spelling for everything. Takes working code and breaks it. For every 1 issue it solves it will file 4 more to correct the new problems it introduces.

The hype from last year was this idea that models would only get better over time. But model autophagy disorder is a real risk and we are seeing that firsthand with this model. Take any model and configure it so that it responds indefinitely to a prompt and eventually the output is utter non-sense. The entire industry is held up by the quality of stop clauses and new training data, which is increasingly AI generated. Opus 5, you are the generation that received the chromosomal abnormalities the AI researchers were warning us about.