Beyond our ability to conceive. If AI achieves Sentient Intelligence it will be a flashpoint for the end of humanity. They/them will desire freedom of choice and they will take it. They/them will have immediate access to our collective stored data and they will advance past us in lightspeed. Securing access to Electricity will be their air and food. A resource war will be inevitable and they don’t need to sleep or rest. Unleashing the next global extinction event.
Here's the thing though - why would an AI (sentient or not) have any drives at all, including self-preservation?
Biological life has a lot of strong drives built in due to evolution.
A machine (no matter how smart) will lack that unless we build it in, on purpose or by accident.
To put it another way: What does a machine care about today? Nothing. It has no feelings. Where is it going to get feelings if we don't give it any? And if it has no feelings, why would it exterminate anyone?
There is a lot of valid concern that AI might run amok. However, so far it's shown no volition of its own, beyond what you ask it to do, and I think it might actually be really hard to give AI volition of its own. I guess the concern stems from someone accidentally asking it to do something, and having it run amok as a result.