I don't wish to suggest that Actemra is a perfect solution for PMR/GCA. My rheumatologist didn't make any guarantees that Actemra would work. He just wanted me to try Actemra because he didn't want me to take prednisone for the rest of my life. I'm happy that I tried Actemra.

I think corticosteroid dependence and adrenal insufficiency due to a long term prednisone use was a significant part of my problem. Those symptoms took a long time to improve after I was able to taper off prednisone.

I don't know if Actemra will ever be discontinued. However, biologics in general have a tendency to stop working for the reason that is explained in following link.
https://www.verywellhealth.com/antibodies-to-biologics-4846279#:~:text=Because%20biologics%20are%20created%20using,different%20for%20each%20individual%20drug.