The download size of games these days can be quite large, but updates and DLC's are usually limited to small portions of precious GB's of data. Unfortunately, there is a current issue on the Windows 10 version of Forza Horizon 3 where you might receive a prompt for a 53GB update, and the Forza team wants you to know that they are currently investigating it.
We're aware of and investigating an issue where #ForzaHorizon3 on PC is prompting players to download a 53GB update.
— Forza Motorsport (@ForzaMotorsport) January 3, 2017
From the tweet seen above, it is not immediately clear what caused the prompt for the download, or how it will be resolved, but it is still reassuring to see that the Forza team is working on finding out the root cause of the issue. We will be monitoring the situation right along with the Forza Motorsport team and will update this post once more details have emerged. Until then, we invite you to check out our Forza news hub, to make sure you stay up to date on all your Forza news and information.