IPv6 in Azure VNET is currently previewing globally- in ALL Azure Public cloud regions.
Announcement (Service Update): https://azure.microsoft.com/en-us/updates/public-preview-microsoft-adds-full-ipv6-support-for-azure-vnets/
Links to Documentation & Samples
Full documentation including sample scripts is available here: https://aka.ms/IPv6ForAzureVNETdoc
A sample JSON template is posted in the quickstart repository: https://azure.microsoft.com/en-us/resources/templates/ipv6-in-vnet/Jeff Schulman commented
We require IPV6 for the management network in order to use Azure Stack.