It depends, some times I've seen them replace the arm but transfer the cobra but some times they replace everything, I've also seen them transfer the old arm and fixture. Sometimes they also completely remove the light and arm and never replace it
They usually replace everything in my area when they renew poles now...only problem is they trash a perfectly working fixture, install a FCO fixture in a row of drop lens lights, and they'll sometimes use a shorter arm...ugh looks tacky imo
These arms appear to be of an Canadian design, as they have unique brackets. However, I have seen some of these same arms here in California in cities with their own electric utilities. Burbank and Azusa have a few of this type of arm, I should take a pic.
The arm bracket looks like one of these Al-Struct arms but it might have been a Powerlite design since their traffic signal hanger looks identical to the Powerlite one.