On July 25, 2016 Microsoft released the first update for SQL Server 2016. This cumulative update #1 provides resolution for 171 separate issues across 40 separate aspects of their latest release of the flagship data product for the company.
The build number for this release is 13.0.2149.0 and is available for download for free and without registration from the Microsoft Download Center. Keep in mind though that location only hosts the most recent Cumulative Update (CU). After CU 2 for SQL Server 2016 is released you'll need to navigate to the Microsoft Windows Update Catalog to download CU1. However Microsoft always recommends downloading, testing, and applying the latest CUs, Service Packs, and Hotfixes for SQL Server 2016. Cumulative Updates are held to the same rigorous standards as full Service Packs.
The list of fixes released as part of CU1 is available from Micrsosoft here.
It should be noted that Microsoft does state that a reboot may be required after installation of this Cumulative Update.