It looks like it is not a free trial but free with use limits.
IE You can use it for free forever, but just not too much each month. Pay for more CPU time after you hit your limit or wait until next month to get more free time.
It looks like there's also a 30-day limit on "deployments" in the free tier. It's not 100% clear to me what that means, but I'd guess it means public-facing apps built on top of the API need a paid account to deploy more than as temporary/test setups.
IE You can use it for free forever, but just not too much each month. Pay for more CPU time after you hit your limit or wait until next month to get more free time.