It took 4 years to develop the basic ideas for the Reclaimer Trilogy story arc and Halo 4. Those first four years were spent doing a lot more than just Halo 4. The Reclaimer Trilogy was planned out in advance. Compare this to Bungie's Halos where CE was originally intetended to make a single Halo Mac game that was pushed as a FPS after a few evolutions for the original Xbox. As for Halo 2, within the first two years, the plot was set so it would be the last Halo, but its development screwed up pretty bad and Bungie had to redo just about everything (cutting out about 3-5 hours of extra content from the campaign alone). Halo 3 is another example, the 360 just wasn't capable to push the graphical quality of the Halo engine shown during Halo 3's E3 '06 announcement. Also, Halo 3 was the first to have a abnormally short campaign that felt rushed. ODST was meant to be a add-on, but Bungie used it as a extra title to get out of MS's contract along with Halo Reach. Halo Reach was incredibly rushed because over time more and more people from the Halo team were moving on to Destiny. 343 started production on H5 before Halo 4 shipped (this we have actual confirmation of and is typical of the majority of developers to do), and on top of that, they almost never had a complete team at 343i throughout Halo 4's dev cycle. This'll be the first time 343 creates a Halo game with a full team; they had been building as they went. For Halo 5 they already have the manpower and resources to start with, everything they do from now on will be building off of Halo 4 in a more organised manner. They have an at least 2 and a half year dev cycle on this new game. Who knows how long they've had access to Xbox One technology? They also have the largest team with access to the most resources in the franchise's history. 2 and half years is perfect--Halo remains relevant, and they can still develop a solid game. Rumours and leaks have suggested that developers have been playing around with Xbox One's technology since January of last year, since 343 are a company owned and created by Microsoft (put in charge of the Xbox's most iconic, best selling title) you can bet that 343 had one of the first slices of that particular cake.