Winter Express was a much-beloved Apex Legends mode, introduced late last year over the Christmas period, that changed-up the usual order of business in favour of quickfire rounds between three squads. Built around battling for control of a train, 'the Holiday Express', the mode slightly re-jigged map elements like ziplines and packed the squads into close proximity: it was fast, frantic, had amazing music, and was gone too soon.
But it's coming back. As part of the hoopla around Apex Legends' new Season 7 content, Respawn developers took part in a livestream discussing the patch. It's fairly long (and interesting!) but at around 31:40 the screen shows the main menu's 'timeline', which tells you what your mates have been up to. And it shows that Respawn's mates have been playing a bunch of Winter Express.
Here's a screen of the moment in question.
In addition to this, the current update has also added badges (Apex's in-game achievement system) that reference both Winter Express and... the 2020 Holo-Day Bash. The first version of this event introduced a bunch of cosmetics and challenges, as well as the Winter Express mode, and was the first time I'd ever seen a gun decked out in candystripes and a jolly festive scarf.
There's no official word on when this all kicks off, though perhaps worth noting the 2019 Holo-Day Bash ran in-game from December 13, 2019 to January 7, 2000.