The new joint membership was announced last month (or earlier this year) but new to me. I recently renewed my USAT membership but before I started Crit racing. I searched both the USAT and USAC sites for info on an ‘upgrade’ program with no luck. I emailed USAT Membership Concierge and they quickly sent me a discount code for a USAC membership.
Just thought I’d share in case any else is interested.