The last TWO are 2 hours each, ie, 4 episodes condensed.
Much like the last episode of previous years ... I think the last episode of Season 3 was 1:45 or there abouts.
I found this as well :
Stranger Things season 4 consists of nine episodes in total, each of which runs over one hour long. Most in
Stranger Things season 4 volume 1 average 75 minutes long (or longer), with one being a little less, just over 60 minutes long.
Stranger Things season 4 volume 1 has seven episodes, taking the bulk of the season's content. Meanwhile,
Stranger Things season 4 volume 2 will have two episodes in total, wrapping up the latter part of the season. However, episodes 8 and 9 are feature length, with the finale being almost 2.5 hours long. Throughout its run, the only other time
Stranger Things had nine episodes in one season was season 2. But since each episode this season is over an hour long,
Stranger Things season 4 is technically the longest season ever released.