I have been reading about this topic on Toyota Prius groups and forums online and here is what current Prius owners say about the frequency of changing their hybrid car's cabin air filter.
Someone said he replaced his Prius' cabin air filter after five years. Another person said he changed his 2012's at 65K miles. He says it was a bit dirty when he changed it. Usually 65K miles means the car is about 4-6 years old depending on your driving habits.
Mine is a 2012 Toyota Prius and I haven't yet changed it. However, I feel that it's about the time as when I start the car the initial smell is not very pleasant.
I also read about one person, and I am sure he is not alone, that he changes his cabin air filter once a year. His argument is that you are breathing the air it filters. Apparently even changing the air filter once a year makes a difference. When you replace it even once a year you can see how dirty it is. As I am writing these lines I am thinking to change my car's air filter tomorrow or int he upcoming days.
But some people say they don't change their Prius' cabin filter because they drive in places where the weather is mild and the drive their windows down. This means they are not using their AC that often.
When the air in your new Prius is not smelling good get the AC checked too. Sometimes it may be something other than a filter.
Air filters are cheap. It would be good to pop it out and take a look once in a while. In fact, it wouldn't hurt to pull it once in a while knock some of the larger stuff out of it.
Here is how to change your air filter on Toyota Prius
Getting to it is super easy. Go to Youtube. There are likely a bunch of videos. In fact, on 2010 Prius and a 2007 RAV4 the air filters are behind the glove box. It takes about 5 minutes to change.
Here is a short video showing how to change Toyota Prius Cabin Air Filter in 5 short minutes.
By the way, does your mileage drop when you turn on the AC? Here is how much Nissan Leaf mileage drops when the owners turn on the AC.