And that's better? Isn't that just SMS autocomplete?

Better? I am not sure. A parent comment [1] was suggesting better LLM performance using completion than using chat. UX wise it is probably worse except for power users.

[1] https://news.ycombinator.com/item?id=46113298

If that's SMS autocomplete, then chatLLMs are just SMS autocomplete with sugar on top.

That's what I have always thought. SMS autocomplete with more intermediate iteration and better source data compression