You no longer have to subscribe to one of AT&T's newer plans to get a proper taste of 5G. The carrier is adding 5G and "5G+" (its nickname for millimeter wave 5G) to some of its legacy unlimited plans, including the simply titled Unlimited as well as more advanced tiers like Unlimited & More Premium. Everyday users should see 5G beginning in March, while business customers on older plans will get 5G data starting in April.
You'll need a 5G-capable phone (real 5G, not 5G Evolution), and you'll get an email or text message when 5G comes to your plan.
The legacy support is part of a broader 5G strategy for 2021. AT&T hopes to have millimeter wave 5G in 17 sports venues by the end of 2021, and hopes to start rolling out its C-band wireless spectrum around the same time. In other words, it's shifting from deploying basic coverage to raising average speeds and filling gaps.
The legacy support is a break from the early days of 5G, when carriers (including Engadget parent Verizon) wanted to charge extra for 5G and otherwise steer customers to newer, likely more expensive plans. It's unlikely to be an altruistic move, of course. You might be less inclined to switch providers if you know you can get 5G's higher speeds and lower lag with your existing service. It could be worthwhile for AT&T to sacrifice a little extra revenue from subscribers if it means keeping more customers in the long run.