[modeless]

I disagree. These special APIs will not have the breadth of capabilities that the human UI does, so AIs will use the human UIs out of necessity. But I think in the long term we will eventually see a simplification of UIs. As it becomes less common for humans to actually use them, they will no longer need fancy animations or dark mode or client-side validation or pretty styling. In the extreme, a return to plain HTML forms that a human can use in a pinch but are mostly used by AI agents. At that point I guess you're blurring the lines between UI and API.

[usrusr]

Isn't it the exact opposite? Interfaces we use every day can be dead simple, all they need is that they don't change behind our back. The accelerator pedal does not come with a footover pop-up "keep pressed to make car go". Interfaces we use once in a leap year on the other hand, that's where we need all the hand-holding we can get.