IOP (under regular circumstances) in the hospital I used wasn't much different from inpatient except the IOP patients could go home at the end of the day.

I'm guessing much depends on the program. The hospital programs were psychoeducational groups (teaching about mental health concepts, skills - like CBT/DBT,etc.), process groups (just sort of talking about what is going on, but not really as personal as an actual therapy group - more about issues within the program itself), and goals/commitment groups are pretty much what they sound like (set a goal for the day or sometimes these were 12-step groups for patients who were there for chemical dependency).

Often you don't have a therapist of your own. I think IOP patients touch base once or twice a day with a social worker or therapist very briefly.

Don't expect deep digging like you would in individual therapy. Normally, that's not an IOP thing.

My understanding about IOP was that it was a way to stay sort of structured in your daily mental health care, with some supervision, for a period of time, while you stabilize.