Microsoft works heavily on their Microsoft Azure Recovery Services and releases new features for its Azure Backup software. Some of these new features need a new version of the Azure Backup Agent, or MARS Agent, to work.
Now if you install a new recovery vault in Azure to get started with Azure Backup you will find a link to download the Azure Backup Agent or sometimes you will see warnings in the Azure Backup MMC console with a link to a newer version of the Azure Backup Agent. But if you just want to download the latest MARS Agent, sometimes it is pretty hard to find, so let me help you with this link:
You can also use that file to updated an existing Azure Backup Agent.
By the way, Microsoft Azure Backup now supports Windows System State Backups to Azure.