The writer and director - who is also DC Studios co-chief with Peter Safran - has given a major update on his upcoming superhero blockbuster after a six week shoot in Cleveland, Ohio.
He clarified on Threads: "We are not done shooting. Still a couple weeks left. Just done shooting in Cleveland".
"And yeah it's a long shoot... but we're getting close!!".
The film stars David Corenswet as Superman/Clark Kent, while Rachel Brosnahan has been cast as Lois Lane, and Nicholas Hoult will play Lex Luther.
Gunn expressed his gratitude for the city of Cleveland, hailing it a "special place".
He wrote: "Cleveland - today we are leaving you after six amazing weeks of shooting".
"From the moment we first came here on a scout a tad less than a year ago and Terminal Tower was lit up with the colors of Superman, I knew you were a special place".
"I would walk down your streets and someone would stop me and tell me how grateful they were we were shooting in their city - not once, not twice, but dozens of times".
He also heaped praise on the "wonderful background actors" for helping remind him why he loves making moves".
He continued: "The wonderful background actors on the film were always so fun and funny and they clapped after takes, something that reminded us Hollywood cynics why we make movies in the first place".
"The pride you feel in being where Jerry and Joey first created Superman was invigorating. You exemplify his spirit".
"But just as much it's the pride you have in your community, your hometown, your radio stations and restaurants and gatherine places that touched me".
"Every city would be so lucky to have people that loved their city as much as you. You simply couldn't have been more wonderful, kind, or accommodating to me and our performers and crew".