@Bento Guida Welcome to the Microsoft Q&A forum, Thanks for posting your question.
With the “longer commitment” you can refer to ‘Azure Reserved Capacity Pricing’ which is much more economical when compared to the pay-as-you-go pricing, when the reservations are made within a 1-to-3-year timeframe.
We have explained this here in this Learn article - How to optimize costs in Azure Database for Postgres Flexible Server.
I hope this information helps, please let me know if you have any additional questions. Regards Geetha