Unfortunately, there wasn't much in the way of detail on how these features will actually work when they roll out this fall, but at the very least Microsoft appears to recognize the fact that it's still rather hard to get good multiplayer games going -- or knowing when particular friends of yours want to play specific games. Microsoft said this update would come this fall -- presumably with the Xbox One Windows 10 Anniversary update that'll bring Cortana to the system.
Update: A Microsoft blog post has filled in some of the details about how these features will work. Clubs on Xbox Live will work across Xbox One, mobile devices with the Xbox app and on Windows 10, with content sharing, chat and more.
The Looking for Games on Xbox Live (LFG) feature will bring "want ad" style postings to XBL, that let you find gamers with the right capabilities and priorities to match what you're trying to do. We've seen LFG services crop up around many multiplayer games lately, and Microsoft's version has all the usual OkCupid-for-gamers features, with specifications for things like ranking, using a mic, and lets hosts approve interested gamers.
There are fewer details mentioned about Arena, but it should help surface competitive gaming for potential players and spectators alike. Microsoft is teaming up with established names like FACEIT, ESL, MLG and others, and says a Killer Instinct tournament is coming via the FACEIT app this summer. The Arena feature handles details like registration and results reporting, and can launch gamers directly into a match.
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