I’m my high school we don’t have IB or AP courses, but we have GAC courses.
As far as I can tell, no the UC schools do not accept Global Assessment certificates. If you go to the official website for the GAC, you can see which schools do accept it in the U.S. https://global.act.org/content/global/en/global-programs/pathway-universities.html None of the University of California schools are listed.
You can however, consider reaching out to the school or contacting an admissions bot on the website to see if they really do not accept the GAC.
Hope this helps! Best of luck!
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