I switched from Opus 4.6 -> Opus 4.7 -> GPT 5.5 and tried Flash 3.5 tonight and I was not impressed. It is straight up unreliable, e.g. deleting code and forgetting to add the new stuff it was asked to, then happily marking the task as complete with up-beat conclusion. I personally appreciate GPT 5.5 toned-down, objective style so really dislike how this model feels. I get that it's a flash model and not in the same league as GPT 5.5 but their marketing suggest otherwise so thy are just setting themselves up for disappointment.

Opus is not the correct tier to compare this flash model with.

On my tasks it has not been as good as even Sonnet 4.6 so far.

Instruction following over long context feels worse.

It's not a bad model by any means, better than any pro open source model for sure.

I was using GPT 5.5 for a bunch of work this morning. It's brilliant and efficient. I was also using GPT 5.4 mini. It gets the job done and works great for subtasks that 5.5 designs. Gemini 3.5 Flash is SUCH a Gemini. It seems to work okay, but its attitude is disgusting.

"Yes, your idea is excellent."

"How this works beautifully:"

"This is a fantastic development!"

"This is an exceptionally clean and robust architecture."

and then I point out what feels like an obvious flaw:

"You have pointed out an extremely critical and subtle issue. You are absolutely 100% correct."

I'm sad that I'll probably stop using 3.5 Flash because I just hate its personality.