I already own Killer Instinct for Xbox One, do I need to re-purchase my content in the Windows 10 version?
No, you do not need to re-purchase anything you’ve already purchased in Killer Instinct. In fact, everything you own and have earned in Killer Instinct is available to you on Windows 10.
In order to access your existing Killer Instinct content on Windows 10, Xbox One owners must receive the Season 3 game update, available starting March 29, 2016. Simply login to your Xbox One console and launch Killer Instinct. Ensure you’re connected to Xbox Live and follow the prompts to receive the update. Once the update is complete, launch Killer Instinct fully. Once the update is complete and you have launched Killer Instinct again, you will be able to login into Windows 10 to access your owned and earned content.