How often do you anneal your brass?

I don't anneal. I've been close to buying an annealer and getting into it, but I haven't personally seen any negatives to not annealing. I think there's merit to it for sure, but I don't think it's a necessity. That's just my opinion and experience, and it may change.
So if you’re shooting new brass when do you start annealing your brass and then after you start how often?
Every firing!
Most of my cartridges are an improved design. So I anneal prior to fireforming and then I anneal after every firing. Whether or not it helps in terms of performance I can't say but in theory my brass should be consistent every time after annealing. I don't know that the stress induced when firing and resizing is consistent, but at least I know that I am as consistent as I can be by annealing every time.

I use an AMP annealer so it's ridiculously fast.
I do fully believe annealing needs to be done right in order to get the full benefit and consistency from it and that comes from experience both by doing (multiple methods) and by research on the process and science itself.

I do agree that if it’s not being done right/properly, and each piece isn’t getting perfectly annealed, you’d actually be better off not annealing and letting the brass just work harden. As long as your steps in reloading are the same, the brass will remain consistent to one another, you’ll just be increasing the effects of the work hardening on the brass as you go. Of course, if you’re using lower tier brass and it’s inconsistent on thickness and other areas, it’ll continue to be inconsistent as it work hardens and neck tension can vary as a result. The fix there is just use top tier brass 😉.

So with all that said, I recommend to anyone that if you’re going to do it, do it right or don’t do it at all.
One could buy a lot of brass for the cost of an AMP 1500.00.
True, but brass is a consumable and eventually that brass will unusable and need to be replaced. An AMP is an investment. It’ll keep all that brass consistent and make it last longer, if you’re not pushing pressure to the point your primer pockets loosen up quick. Annealing won’t help you there.

To each their own though. You don’t NEED an AMP to achieve proper annealing either. It’s just the easy button.