Amazon have announced that they are scrapping the ‘Underground Actually Free’ programme.
Starting from May 31st 2017, users will no longer be able to submit apps and games for the service, and current support for the programme will end in 2019.
Until that time there is no change to the terms if you are currently a developer using Amazon Underground and you will continue to earn for every minute a customer spends in the app. The Amazon developer blog, which announced this change, also had these points –
The program has been in place since 2015 and Amazon have said "we added thousands of apps, expanded internationally, and added support for Fire tablets. At the same time the Amazon Appstore increased selection to offer more than 800,000 apps and games while expanding our footprint across a growing portfolio of Fire tablets, Fire TV, and Android devices as well as 236 countries and territories worldwide."