Thank you all for your feedback and thoughts on this hand.
Much appreciated, as always!
I'll post the results at the bottom of this post but let me get to all of you first.
I literally don't know how to play this deep.
My intuition is telling me that I would just fold preflop, but I don't know if that is good advice.
Well with late registration you rarely get this deep, so I see your point.

Any advice is appreciated, so thank you!
And while I see that ATs is not the best hand in a 3-bet pot, I assume(d) since we're both in late positions, both the opening and 3-bet ranges are a little wider than if it was UTG vs. UTG+1. Here I might have folded this hand indeed.
you will be shown an overpair, a 7 or 98s alot. His flop sizing is also pretty big popularizing right from the start, which suggest a draw or thick value. In theory he shouldn't be bluffing missed flush draws on the river, so it lends him toward 98, 87 or 76 maybe AA with weaker overpairs often getting checked back.
Do you think he would 3-bet 98s? That 3-bet range would be even much wider than I assumed. I also didn't assume he has a 7, since there are already 2 on the board and I'm not sure if A7 would be in the 3-bet range but ofc nothing is impossible.
And to the bet sizes: I have seen people c-betting with all sorts of sizes from 20% of pot to half pot, so that did not worry me too much. But indeed, I need to learn to evaluate all the information.
You weren't tempted to bluff raise all-in with the top boat blocker then?
Haha no, I do not have all those fancy plays yet in my books.
This deep you can open bigger than 2,5BB.
So something like 3 BBs? Or even more? I would have opened 3 BBs indeed but Idk why I didn't do it here.
he could certainly have 98s.
So you agree in would be in his 3-bet range? I honestly did not even take it into account.
He could still have busted spades or be bluffing with just two overcards. But without reads I prefer to fold.
I totally agree here. Most players slow down their c-bets after one or even two streets. But three barrel bluffs occured to me very rare and there might be much better cases to put so many chips in.
Every time I see this....3bet pre-flop and the bet bet bet....in my case when he bets 2/3 pot on the river he has something like JJ+...even like that with your cards top pair top kicker I don't think I would fold either.
Thanks for this honest feedback. At least it's nice to see someone agreeing it was sorta hart to fold.
Is it early in the MTT? Is that why everybody is so deep? Is this also why you decided he might be bluffing?
Yes, it was only a few hands in. On flop, I would never fold my TPTK since it could also just be a c-bet. But I agree, I should have put in some more thinking on Turn and especially river.
Preflop you are calling a 3-bet with AT OOP - for what purpose?
We are both in late-ish positions and since my raising range is wider, I'd assume his 3-bet range is a little wider too.
If you 4-bet him preflop then you might find a fold if he 5-bet shoved?
If you check raise him on the flop - then you might find a fold if he shoved?
Absolutely a "yes" to both questions. Are you asking to trigger my decision to fold or are those actual suggestions for playing this hand?
Of course, if he had 85, then I hope you destroyed him later on.
That's not what he had but I also did not get the chance to destroy him since I was moved tables a few hands later.
So a very learningful, hard hand. Thanks for posting!
I'm also learning by every hand I post, so glad you enjoyed this thread.
I don't understand what you were doing calling every street tbh.
I don't donk bet very often. Except as c-bet when I get other callers. Otherwise I let the pre-flop raiser take the lead.
But I see your point that it would be an option here with my unclear TPTK.
As most of you have already assumed, he had an overpair indeed.
It wasn't the Aces, Kings or Queens but the Jacks.
I really appreciated all of your feedback and will try to keep it in mind in a similar situation like this.