[Update: Further information from Microsoft has led us to correct and amend significant portions of the analysis in this piece related to undercounting of usage data. Please read our full explanation of these corrections.]

For three years now, Ars’ Steam Gauge project and the public sampling projects it has inspired (such as Steam Spy ) have provided an important behind-the-scenes look at what kinds of games are popular on PC gaming’s most popular marketplace. Today, after years of work, we’re ready to unveil a new effort that similarly uncovers what’s popular among Xbox Live users on the Xbox One and Xbox 360.

As we introduce you to our data and our methodology, you probably won’t be surprised to see the enduring popularity of franchises like Call of Duty, Grand Theft Auto, and Halo on Microsoft’s platforms. You might be more surprised by just how often the average Xbox console is used as nothing more than a streaming video box, or by how a relative handful of games dominate the total play time spent on both consoles, or by the specific, branded Xbox 360 adver-game that still sees relatively significant play years after its release.

We’re just beginning to play with all the data about Xbox Live users we now have at our disposal. But first, a little about where that data comes from.

Opening the box

Shortly after I published my first Steam Gauge analysis, I realized something similar might be possible for the world of Xbox Live. You might not realize it, but Microsoft generates a list of every game that’s owned by every public Xbox Live account, and that list can be easily accessed by anyone who knows the Gamertag in question. You can see this for yourself by navigating to the Profile page for pretty much any arbitrary Gamertag on Xbox.com and clicking the Achievements tab (You’ll need to sign in with your own Xbox Live account to access this page—a free silver account will do).

Even games where the owner hasn’t earned Achievements yet, or hasn't even played the game yet at all, seem to show up in this listing. Here’s my profile as an example. Here’s one for Xbox community manager Larry “Major Nelson” Hryb.

This listing covers both online and single-player games, and it seems to be updated as soon as the game is first played on the console (Update: We originally said games showed up here as soon as they were purchased digitally. Ars regrets the error). The listing even shows certain PC games that connect to Xbox Live through the Xbox for Windows interface, though we’re not clear which games trigger that as of yet. And while users can decide to block this information from the public in their Xbox Settings, very few seem to go to the trouble.

Xbox.com isn’t the only way to gain access to this kind of Xbox game-ownership data, though. Thankfully, the folks over at XboxAPI.com have created an easy-to-use service that spits this kind of information out in an easy-to-parse JSON format, suitable for easy insertion and manipulation in a database. By randomly sampling this information over time (more on this below), we can get a robust sense of what proportion of Xbox Live users own each game in a system’s library. While we don’t have any particular inside knowledge of precisely how XboxAPI generates its information, the data seemed perfectly reliable when we tested it on our own Gamertags and our own gameplay and ownership patterns.

The information available via that API actually goes well beyond mere game ownership—or, rather, it did until recently. For quite a while, XboxAPI also provided a wealth of information on the games that Xbox Live users had actually played over the last month, including when they played those games and for how long. Using that data, for example, I could have told you the precise time and length of each of Major Nelson’s frequent gaming sessions over the past 30 days (though of course I wouldn’t, out of respect for his privacy).

Microsoft appears to have stopped surfacing this kind of extremely granular Xbox Live usage data sometime in mid-February, which is probably a good thing from a user-privacy perspective. Before the company turned off this data spigot, though, we were able to randomly sample the Xbox-usage activity of hundreds of thousands of active Gamertags over a period of more than four months (see below for more on how we did that sampling). This has allowed us to create a wide-ranging, anonymized, aggregate look at what the average online Xbox 360 and Xbox One owner was actually doing with their systems on a day-to-day basis during that time.

Tagging those Gamertags

With an API data source in place, we only needed one more piece to start generating our sample: a comprehensive list of Xbox Live Gamertags. Unlike Steam, which assigns its users semi-hidden numerical IDs in more-or-less sequential order, the Xbox API only spits out data when given a user’s chosen Gamertag. Getting a complete list of all such Gamertags (or at least a suitably large and representative subset) to sample from was not an insignificant challenge.

After a lot of searching for a way to get at those Gamertags, I stumbled on a gold mine. Buried in the achievement leaderboards on XboxLiveScore.com was what seemed to be an extant list of over 48 million Xbox Live Gamertags (the site is offline now, but you can browse a limited copy on The Internet Archive).

It’s unclear to me if this list came from the now-defunct Xbox Community Developer Program (which once powered excellent sites like MyGamerCard.net) or from the site’s owner simply scraping of the public Xbox.com site. It’s also unclear how up-to-date the list was when I found it in 2015, though it had certainly grown considerably since starting with about six million Gamertags back in 2011.

Regardless, this was just the kind of find we needed to get things going. As we started developing and testing the API and database algorithms that would eventually power our reports, we also started expanding our Gamertag list by looking at the friends lists of every user we touched on. If any of those friends’ Gamertags weren’t in our database, we added them. This expanded the total possibility space for further sampling going forward.

After running this process for many months, our initial list of just over 48 million Gamertags is now approaching 74 million (73,928,903 as of this writing, to be precise). Considering that Microsoft reported only 55 million active Xbox Live users at the beginning of 2017, we feel that’s a pretty good sample space, even accounting for the mass of “inactive” and/or defunct Gamertags that are doubtlessly wasting space in our list.