Azure Reservations for the Azure SQL Database service became available earlier in August 2018 (see our blog post here: http://bit.ly/2KROzpp). If you want to understand more about how the reservation discount is applied automatically to running Azure SQL Databases then this is a useful article: http://bit.ly/2vX61UR.
There’s a brand new SQL Server 2017 Licensing Datasheet to support general availability of this product on 2nd October 2017. There aren’t changes to the fundamental licensing but this datasheet is a nice summary including useful information such as the differences in SA benefits between Standard and Enterprise editions.
Find it in the Application Servers section here: http://bit.ly/MSLicensingGuides.