Been watching the Claude Opus 5 discourse since it dropped, and honestly it's kind of a mess. Half the people in this sub are calling it a massive upgrade; the other half are saying it hallucinates more than 4.8, fights instructions, and feels like a step backward. We wanted to actually figure out what's going on, so we ran a proper comparison, and the finding is kind of counterintuitive.

So everyone's been leading with the same three things. Half the price of Fable. Big ARC-AGI score. Here's a racing game it one-shotted. All fine, but none of that actually explains why people's results are so wildly different from each other.

# The effort setting is kind of the whole story

Opus 5 has an adjustable reasoning effort level. Dan Shipper's team at Every had it a full week before launch, and their main takeaway was pretty surprising: the model consistently does better at medium or low effort than maxed out. His framing was that it's a smart model that does better when it thinks less.

Anthropic's own Claude Code team also mentioned separately that they stripped over 80% of their system prompt on newer models and saw no drop in performance. Less overhead, not more.

# Also, your old skill files might just be the problem

Shipper's team was running into the exact stuff people are complaining about in this thread. Stopping early, arguing with instructions, breaking existing plugins. They deleted all their skills and rebuilt from scratch, and results got noticeably better.

If you're testing it with a setup you already tuned for 4.8 or Fable, there's a real chance you're stress-testing your old configuration more than the actual model.

One more thing on the pricing: the per-token rate is genuinely half ($5/$25 vs $10/$50). But Opus 5 reasons for longer, so actual spend per task can end up higher than you'd expect. Worth checking your real bill before migrating anything serious.

We ran the same brief at max effort, medium effort, and alongside Fable with full token spend breakdowns in the video above if you want to see the actual comparison.

Has anyone actually tried turning the effort down yet? Did it change anything or is it still feeling off regardless?

Claude Opus 5 feels totally different depending on how you're using it, and the effort setting is probably why