I think that very much depends on the Stammtisch. There are also welcoming ones and open ones. Some you might have to RSVP for, some you hear about from friends.
Funny how this whole reply of me was just a misunderstanding after reading https://news.ycombinator.com/item?id=42497747 and even more funnier I'm doing this and most of my friends but nobody calls it Stammtisch here. It's usually just called Treffen. Stammtisch is so hard wired in my brain to bars full of smoke and people drinking beer at a table called Stammtisch.
It's all a complete confusion. My comment has little to do with your comment. It's two completely separate things.
