One of the first questions to ask about any group, and one people rarely think to ask.
Closed groups
Everyone starts together on a date and finishes together. No new members after the first week or two.
What that buys: the group moves through stages together. Trust builds on a predictable curve, and by the middle sessions people say things they wouldn’t have said in week two. There’s no repeated resetting.
What it costs: you wait for the next intake. Miss a start date and it may be three months. And if the composition turns out to be wrong for you, there’s no adjusting it.
Nearly all skills and CBT groups are closed, because a curriculum needs everyone at the same point.
Open groups
Members join and leave on a rolling basis. Someone finishes, a place opens, a new person is screened in.
What that buys: you can start when you’re ready rather than when the calendar allows. You can stay as long as it is useful — some people are in an open group for years. And there are always people further along, which does something specific: watching someone two years in do the hard thing lowers the bar far more than being told it’s possible.
What it costs: the group re-forms every time someone arrives or leaves. A new member changes the room, and the group spends a session or two absorbing it.
Most long-term process groups are open, and they use the arrivals and departures as material rather than treating them as interruptions.
Drop-in
A third category, and worth separating. No commitment, different people each week, come when you want.
Almost always support groups rather than therapy groups, and frequently peer-led. Genuinely valuable for access — free, immediate, no screening — and structurally unable to do the work that depends on the same people being in the room over months.
If you want somewhere to go this week, drop-in is the answer. If you want something to change, it usually isn’t.
Which to choose
Closed if you want a defined end, a curriculum, or the reassurance of knowing exactly who will be there. Also if you’re anxious about the format — a fixed cast and a fixed finish is considerably easier to say yes to.
Open if the work is long-term and interpersonal, or if you can’t wait for an intake date.
Ask at the screening call, along with how long the group has been running and how often membership changes. A group that has turned over three times this year is a different proposition from one with the same seven people for two years.