We already know what will feature in Forza Motorsport from launch, but more is coming in a series of monthly content updates.
Turn 10 announces changes to Forza Motorsport's progression system
Forza Horizon To Get Monthly DLC Updates - Cheat Code Central
Forza Monthly to Reveal Motorsport Latest and Horizon 5 Series 23 Update, July 17 – GTPlanet
Rumour: Forza Motorsport launches in October
Forza Motorsport Review - IGN
Forza Motorport's first free content update is coming in mid-November; here are the details - Neowin
FM's monthly content plans - Forza Motorsport (2023) Discussion - Official Forza Community Forums
Forza Motorsport launches October 10 - Gematsu
Forza Motorsport release date, gameplay, and trailers
New Forza Motorsport will release October, includes Le Mans and Spa
Forza Motorsport Update 2 Release Notes – November 14, 2023 : r/forza