Microsoft's Major Nelson confirmed that Xbox One will receive support for external storage devices in an upcoming firmware update.
"Lots of good work going on to make the console even better - some you'll see soon, some will show up later," he said on Reddit. Later on, he added a comment stating that "External game storage is coming soon."
Unfortunately, Major Nelson was not able to pinpoint a timeframe for the update to come; nor was he able to give any details regarding supported devices or capacity limits. "When I have details on that , I'll let you know," he promised.
Xbox 360 external storage support is limited to 32GB only.