This is news to me and I don't think this is true... or it's maybe hidden away somewhere. I am a Fi subscriber using a Google Pixel phone but YouTube premium is still $13.99/month.
Unlimited Plus (the plan with free YouTube Premium) is a dollar more per month than just buying the Unlimited plan and YT Premium separately. You also only get it free for a year.
is it? I've had fi for years and never noticed. I also don't watch much yt so it's not something I'm apt to notice I suppose.