Was told (by the hiring contact) that the first round would be an informal chat with the department head regarding my history/ experience/ alignment with company values.
On the day (with no warning) this turned into a 3 person panel technical interview, for which I was underprepared.
The interviewers present were pleasant to deal with, but being blindsided (hopefully inadvertently- if on purpose, this is a sneaky thing to do) left a less than pleasant taste in my mouth. Make sure you get confirmation in writing about the interview format before the interview is conducted.