Do the UC schools pay attention to improvement curves in GPA into senior year, during admissions?

Colleges & Universities University of California - GENERAL
2

I don’t believe they will know unless you tell them.

They make admission decisions primary through your junior year transcript - although they know your current/planned senior courses.

Decision process feels fairly structured:

https://admission.universityofcalifornia.edu/how-to-apply/applying-as-a-freshman/how-applications-are-reviewed.html

Now, there are at least two sections of the UC where you can tell this story - one of the 8 personal essay topics fits this story and there is also a “should we know anything else” prompt.