UPDATE 22/8/14 9.30am Microsoft has claimed that its listing of a new 24-hour free game unlock program was an "error".
In a statement to Eurogamer, the company acknowledged the listing as genuine but described its public appearance as mistake.
"A promotional tile for 'Max: The Curse of Brotherhood' was posted briefly on the US dash in error yesterday," a Microsoft spokesperson said. "We apologise for any inconvenience.
"We're constantly exploring different ways to offer more benefits to our Xbox Live Gold members and will keep them updated when special offers become available."
ORIGINAL STORY 21/8/14 10.10am Microsoft has begun testing a feature which makes Xbox One games free to download and play for a limited period.
US users taking part in the Xbox One console beta last night spotted that Max: The Curse of Brotherhood had been unlocked as a free download (thanks, Reddit).
The popular platformer was listed in the Xbox One's Games with Gold section under a new label - Free Play Day with Gold.
Microsoft has yet to discuss the new feature - we've asking for more details.
The company's official Xbox Support Twitter initially seemed to be surprised by the feature's appearance, but later suggested that an official announcement would be made "shortly".
As currently listed, the Free Play Day with Gold idea looks like it will be available in addition to the standard Games with Gold offering, which makes two Xbox One titles free to download each month if you're a Xbox Live Gold subscriber.