Edit: Seems like there's a 10 year limit in many places? I wonder if that's broad convention or an actual rule.
Okay, apparently an ICANN limit for .com domains:
"The expiration date of the domain registration is extended by the number of years, up to a maximum of ten years, as specified by the Registrar's requested Extend operation."
https://www.icann.org/en/registry-agreements/com/com-registr...
Though, I can see that navy.us has an expiry in 2053, so it's likely per registry.
Edit: CSC, Markmonitor and similar shops will contract to keep your name available for long periods, too, but that's a bit different.
Yearly at least keeps me on my toes a bit.
Also most registrars will send you an email when it's about to expire. If it does get dropped, there's a grave period to recover it.
Edit: It seems to vary. Some places cite an ICANN limit of 10 years.
They are betting that they will earn more than enough from investing your up front 100 year payment to more than cover future increases in the cost of those one year extensions.
Their customers are betting that Network Solutions or some successor will be around long enough and that domain names will work like the do now long enough that this will be worth it.
Sorry that doesn’t answer your question more than “it depends on the entity”.