With Opus 5.5 you can vibe code a whole app without reading the code at all. Obviously you still have to tell it what to make.

With earlier models that doesn't really work. You really have to read the code and watch it like a hawk or it will make a big mess.

To put it another way, with lesser models you have to guide them at a code level. With Opus 5.5 you only have to guide it at an architectural / feature level.