Amar Digamber Patil makes an announcement:
Since SQL database is a native item in Fabric, it utilizes Fabric capacity units like other Fabric workloads. Compute charges apply only when the database is actively used, so you only consume what you need. Storage is billed separately on a monthly basis, as are automatic backups, which are retained for seven days.
Billing for compute usage and data storage for SQL databases in Fabric will commence after February 1st.
Click through for more information, including links to more information regarding billing and monitoring.