A Total War Saga: Troy releases on August 13 to the Epic Games Store. It will an exclusive title for that platform until sometime in Summer 2021, when it will become available for those on Steam. When it becomes available, on August 13, for 24 hours, anyone with an Epic Games Store profile has the chance to claim the game for free.
All you have to do is log not to the storefront, claim the game, and it’s yours forever. That’s all you have to do. There’s no special promotion or requirement to purchase the DLC first. You have to do it within the game’s initial 24-hour launch, and then you’re good to go.
Here’s the link to the store page you need to visit to claim the game. You will need an Epic Games Store account to claim the game, so make sure you have one prepared to log into the storefront with once you arrive. If you don’t, you’ll see an advertisement for the game, a trailer, but you won’t be able to claim it until you create an account.
We don’t know if this deal will happen for those on Steam when it releases in Summer 2021, but it’s unlikely. The Epic Games Store likely struck a deal with Sega to make it an exclusive promotion.