The people who make Chicago Fire know what they're doing. There's a reason the show has been a ratings juggernaut on NBC for over a decade, and why it has spawned an entire franchise. But we are at an influx point in the show's history, and the more we learn about a potential season 14, the more we suspect that the show will look radically different moving forward.
The most obvious reason why Chicago Fire will look and feel different in season 14 (which has yet to be officially confirmed by NBC) is the departure of 51 characters Darren Ritter (Daniel Kyri) and Sam Carver (Jake Lockett). They have been around for seven seasons and three seasons, respectively, and they occupied crucial roles within the firehouse dynamic.
Chicago Fire may suffer more cast exits

Not only will they be missed, Ritter and Carver being gone opens up two gaping hopes within 51 that will need to be replaced in season 14. It's one thing to have to fill the role of one established character but to have to do it with two simultaneously is going to be a tall order. The second reason the show is on the cusp of looking very different is that more cast exits may be around the corner.
Deadline confirmed that NBC is currently in the midst of negotiating with Chicago Fire stars when it comes to their contracts, and given how much emphasis the network has put on cutting down Fire's budget, the outlet noted that we could be getting more surprising exits in the months to come. We might have a firehouse that looks very, very different in the 2025-26 season.
NBC is cutting down on actor episode counts

This emphasis on cost cutting is not limited to the characters who are leaving the show, however. NBC is also looking to potentially cut down on the number of episodes that remaining characters will appear in moving forward. We've already seen the impact of this particular measure, as characters like Violet Mikami (Hanako Greensmith) and Christopher Herrmann (David Eigenberg) have been removed from the episodes that don't explicitly require their presence.
Deadline floated the possibility of seeing more instances of established 51 characters failing to appear in episodes so that NBC does not have to shell out for the entire cast every week. It's not particularly encouraging, given how this practice could start to make the show feel less unified and more compartmentalized than we're used to. Chicago Fire is an ensemble at the end of the day, so we're going to hold out hope that these potential episode constrictions don't get worse.
Chicago Fire season 14, assuming we get it, is going to feel like the start of a brand new era for the show. Because, in a lot of ways, it will be. Let's see what this era looks like.