The Microsoft Office 365 Developer Program is not new, but perhaps some of you are not yet familiar with it. So if you want to try out Office 365 or even develop your own applications for or with Office 365, the Developer Program gives you 25 E3 plans for 90 days free of charge (see note at the end of the article).
I registered on a trial basis on 02.04.2019 and still received the licenses with a one-year term:
Registration is completed within a few minutes and no payment details need to be entered. You can register for the program here:
Note: The Office 365 Developer Program was changed in April. Before April 2019, 25 licenses were still available free of charge for one year; from now on, the 25 licenses will only be available for 90 days:
In April 2019, we transitioned to a new model where your subscription can be renewed perpetually every 90 days if you’re actively using it for development.
Source: Office 365 Developer Program FAQ
So if you are actively working with Office 365, the license will be extended by a further 90 days after 90 days. If the Developer Program is actively used, it should also be possible to use it beyond 1 year. The program is of course suitable not for productive use.