UPDATE 16/5/14 2.20pm: The first slice of concept art from Halo 5: Guardians has been released via Halo Waypoint.
Writing in a blog post there, 343 Industries' Frank O'Connor also emphasised the developer's previous statement that the journey towards Halo 5 in 2015 will begin this year, and that another announcement was seemingly on the way.
"Last year at E3, Bonnie [Ross, 343 studio head] famously said, 'Your journey begins in 2014…'. Wait - hang on - you thought: 'What journey is she talking about and why is Chief wearing a poncho?' Okay, some might call it a cloak, but the fact remains - you knew something more nuanced was afoot. So it's quite likely that Bonnie's 2015 release announcement today surprised no one in the Halo community.
"In fact, I suspect most of you who read the Halo Bulletin regularly anticipate there's even more to come. Well you might be right, but we'll have significantly more to say about that at E3 and beyond. Suffice it to say, another shoe has yet to drop."
ORIGINAL STORY 16/5/14 11.00am: Microsoft has announced Halo 5: Guardians for Xbox One and said that it will be released in autumn 2015.
Halo 5: Guardians is described as a "massive and exciting project" by Bonnie Ross, general manager of developer 343 Industries, who also described it as "the next instalment in the legendary saga of the Master Chief".
"Making a Halo game that runs at 60 frames per second, on dedicated servers, with the scope, features and scale we've been dreaming of for more than a decade, is non-trivial," Ross explained in a blog post on Xbox Wire.
"It's a task that we, at 343 Industries, are taking very seriously to ensure we deliver the Halo game that fans deserve, and a game that is built from the ground up for Xbox One."
"Halo 5: Guardians is a bigger effort than Halo 4," she continued. "That applies to the content and scope of the game, as well as the technology in what's now a brand new and more powerful engine.
"Certainly there are some core elements carried over from prior games, but we've invested a huge effort in retooling our tech to take full advantage of the Xbox One's hardware and ecosystem to create worlds and experiences worthy of next-gen.
"It's a game that will hopefully demonstrate the talent, learnings and abilities of the 343 Industries team.
"A game that will incorporate the things we learned from Halo 4 about technology, aesthetics, performance and scale - and perhaps more importantly, understanding and embracing a community of gamers who love what lies at the heart of this game, and the limitless potential of the Halo universe."
So that's Halo 5: Guardians, then, but Ross also spoke cryptically about the "journey" we're all about to go on. "That journey definitely begins in 2014 with a giant leap, rather than one small step," she wrote.Metal Gear Solid: The first modern video game. The first part of Rich Stanton's series retrospective.
"We'll give you much more information about our plans for this year at the Xbox E3 2014 Media Briefing on June 9, and we're confident that Halo fans will be pretty excited [about] the special plans we have in store."
Whatever could it mean? Some sort of beta? Or perhaps Ross is talking about the Halo 2 Anniversary edition that has been rumoured over the last few months - after all, Halo 2 will be 10 years old this November.
It doesn't seem to be a reference to the TV series that was announced last year, though, because elsewhere in her post Ross makes explicit reference to that also being due in autumn 2015.
A mystery, then, but one we won't have to wait long to solve.