I think one major difference between git and jj is how immutable their DAG is, due to the difference in how they refer to their unit of change (i.e. stable change ID with changing commit IDs vs. immutable commit ID). One implication of that is change history in a git repo feels much more immutable to the one in a jj repo. Consequently operations that involves changing the history like, undo/rebase feels much easier/flexible. Is my understanding correct?

Sorta! I think it can feel that way at times, but also the opposite. jj’s changes are immutable in the same way commits are, when you modify a change, it makes a new immutable commit and associates that with the change. So on the literal level, they’re the same.

But it’s true that mutating history is easy and sometimes even automatic with jj, whereas it’s not with git. So that could make it feel more mutable. On the other hand, jj has the concept of mutable vs immutable commits; jj will present you from modifying certain changes unless you pass in a flag to override it. So in some ways, it’s more immutable than git.

Just really depends on your perspective.