According to a recent post on the Forza Motorsport official forum by community manager Brian Ekberg, PC players were forced to download the full game, which amounts to a 53 GB — a significantly larger file size than one could expect for just seven new, albeit, fancy cars.
Game saves created in this version of the game will be corrupt when started in any other build number, according to Ekberg. Any player who downloaded version .37.2 should uninstall the game, and reinstall version .35.2, as this mishap has since been corrected.
Based on the contents of the wrongly uploaded file, users who downloaded the initial update had actually obtained a developer build of the game. Curious players quickly came across impassable screens displaying debug code. Depending on how you view spoilers, this mistake may be a welcome one, as scores of unannounced cars were discovered.
If you are interested in finding out if your favorite car may soon be available to drive across Australia, a post on NeoGAF purportedly has a comprehensive list of all of the yet-to-be-revealed vehicles. None of the cars found in the debug version of the game have been confirmed for public release by Microsoft. The additional cars found in the cars folder were not playable or even rendered, as they were only visible by name.
The January car pack is officially named the “Rockstar Energy Car Pack” and includes seven cars that have never appeared in the franchise until now: 1972 Ford Falcon XA GT-HO, 1987 Nissan Skyline GTS-R (R31), 2014 Ford #11 Rockstar F150 Trophy Truck, 2015 BMW i8, 2015 Radical RXC Turbo, 2015 Volvo V60 Polestar, and 2016 Bentley Bentayga.
The “Rockstar Car Pack” is the fourth bundle of cars released since Forza Horizon 3 launched in September. Two more packs are expected to round out the planned six in the coming months.