Developer Finds Opus 4.8 More Reliable Than GPT 5.5 For Complex Coding

So I've been using GPT 5.5 and Opus 4.8 for the same tasks basically 24/7 since launch and I suppose this is an unpopular opinion but, at least for me, I'm absolutely certain that *every single time, Opus was superior*, and in a way that is only possible to realize if you know what you're doing. One (of dozens!) of examples: "implement push-pop fusion on HVM4's evaluation loop, aiming for a 20% performance increase" After several minutes: - Opus 4.8 reported it did everything it could but couldn't achieve the goal, and that the performance gain of this change is 7%. - GPT 5.5 succeeded! Its code WAS 20% faster. Upon inspection, it implemented 2 unrelated optimizations that would break HVM semantics in unrelated tests. And was the outcome, 9/10 times. If I hadn't investigated, I'd be disappointed with Opus and use GPT's code, merging a clear regression. Over time, my codebase would accumulate damage. This happened to Bend2! Opus2, on the other hands, was honest, and that negative signal gave me valuable information that pushed things *forward*. I then asked it to try a different thing, and THAT new thing resulted in a legit 25% speedup. That kind of interaction rarely happens with GPT 5.5, in my experience. (I'm not too happy about this post because I'd rather not support a company that gatekeeps intelligence, specially in the context of safeguarding against exploits. Also, your mileage may vary. But I know many follow me for my honest observations and, in >>my<< experience, Opus 4.8 is, without doubt, the most reliable model for work right now.) (This also may sound a bit contradictory because I often praised 5.5 as trustworthy, but I'm talking about different things here. GPT 5.5 is careful, meaning it won't leave things half done: it will cover edge cases, and not declare success until it double-checking everything. In that sense, it is more honest. But it will cheat by malicious compliance. It feels like it is actively trying to game your rules and find loopholes to screw you. I don't feel like that with 4.8 at all.) Note Opus IS still a bit dumber than GPT. It takes longer to grasp a concept. But eventually it does. The more you talk to it, the smarter it gets. GPT is smarter out of the box, but less flexible and less apt to learn new things. Most importantly, though, Opus excels at everything that matters for productivity, including communication, doing what you asked and nothing else, code style, not breaking unrelated things stuff, and, most importantly, honesty. I can't overstate how important all these things are. I'm using it to do a big pass through the whole Bend2 codebase, cleaning up a lot of junk left by 5.5, and things couldn't be going better. I made an incredible amount of REAL (manually verified, not trusted...) progress in the last few days.