The file size should not be too surprising when you consider that Just Cause 3 is a massive open-world game. In terms of map size alone, you will be able to explore 400 square miles. Not to mention that the development team added even more verticality when compared to Just Cause 2.
The third mainline installment of the series is slated to come out on the 1st of December, slightly right after the Black Friday holiday rush. Along with the Xbox One, the sequel will also be released for the PlayStation 4 and PC platforms on the same day.
Up until recently, all Xbox One units came with a 500 GB HDD. Some of the newer models now include an 1 TB hard drive. Fortunately, you can also expand the storage capacity with compatible external HDDs, such as the Seagate Expansion 5TB Desktop External Hard Drive (which you can check out here).