I haven't used Zed much but RustRover seems to have recently switched to a more aggressive/ambitious autocomplete. IIRC tab used to just complete the current word, now it tries to complete the rest of the line. Only it usually gets it wrong. Enter now seems to do what tab used to do and it's been quite annoying having to unlearn tab completing everything.
Maybe Zed's prediction is better (though to be honest I don't really care to find out). But I feel like autocomplete is something where usefulness drops off very quickly as the amount of predicted text increases. The thing is, it really has to be 100% correct, because correcting your mostly-correct auto-generated code seems more tedious and frustrating to me than just typing the correct code in the first place.
It's a new local full-line completion model they've been enabling for one language after another in all their IDEs. I too agree that it's a waste of CPU cycles. The old completion mechanism (a bunch of hardcoded rules plus a bit of machine learning on the side) already was miles ahead of everything else, and with far fewer false-positives.
You can disable it by going into 'File | Settings | Plugins' and turning off "Full Line Code Completion".
Maybe Zed's prediction is better (though to be honest I don't really care to find out). But I feel like autocomplete is something where usefulness drops off very quickly as the amount of predicted text increases. The thing is, it really has to be 100% correct, because correcting your mostly-correct auto-generated code seems more tedious and frustrating to me than just typing the correct code in the first place.