Tickets were still available 10 minutes ago (when I bought mine), at https://www.constellation-chicago.com/event/1579345-28th-anniversary-winter-chicago/ .
I did an advance reconnaissance of the venue last night. As usual, the music was fantastic, the acoustics excellent, the seats uncomfortable, and the room VERY warm. So, be prepared.
(At the venue last night, Hamid Drake and Michael Zerang presented a couple of their other "free jazz" projects (https://www.constellation-chicago.com/event/1601830-trio-waz-tomeka-reid-chicago/ ). Discretion rules, so tonight I will not attend ANOTHER of Hamid Drake's projects there (https://www.constellation-chicago.com/event/1601831-hamid-drake-music-movement-chicago/ ), even though he's the best drummer in Chicago, IMO. When do they sleep?)