A post to the RSI Community Forums by Chris Roberts further discusses the just announced switch for Star Citizen from Crytek's CryENGINE to Amazon's Lumberyard engine (thanks DSOGaming). As noted, the new engine is an offshoot of the old one, and Chris explains that this made for an easy transition:

Lumberyard and StarEngine are both forks from exactly the SAME build of CryEngine.

We stopped taking new builds from Crytek towards the end of 2015. So did Amazon. Because of this the core of the engine that we use is the same one that Amazon use and the switch was painless (I think it took us a day or so of two engineers on the engine team). What runs Star Citizen and Squadron 42 is our heavily modified version of the engine which we have dubbed StarEngine, just now our foundation is Lumberyard not CryEngine. None of our work was thrown away or modified. We switched the like for like parts of the engine from CryEngine to Lumberyard. All of our bespoke work from 64 bit precision, new rendering and planet tech, Item / Entity 2.0, Local Physics Grids, Zone System, Object Containers and so on were unaffected and remain unique to Star Citizen.

Going forward we will utilize the features of Lumberyard that make sense for Star Citizen. We made this choice as Amazon's and our focus is aligned in building massively online games that utilize the power of cloud computing to deliver a richer online experience than would be possible with an old fashioned single server architecture (which is what CryNetwork is).

Looking at Crytek's roadmap and Amazon's we determined that Amazon was investing in the areas we were most interested in. They are a massive company that is making serious investments into Lumberyard and AWS to support next generation online gaming. Crytek doesn't have the resources to compete with this level of investment and have never been focused on the network or online aspects of the engine in the way we or Amazon are. Because of this combined with the fact we weren't taking new builds of CryEngine we decided that Amazon would be the best partner going forward for the future of Star Citizen.

Finally there was no ulterior motive in the timing of the announcement. The deal wasn't fully finalized until after the release of 2.5 and we agreed with Amazon to announce the switch and partnership upon the release of 2.6, which would be the first release on Lumberyard and AWS. If you have been checking out our schedule updates you would know that we originally had hoped to release 2.6 at the beginning of December, not Friday the 23rd!

I hope this clears up some of the speculation I have seen. We are very excited to be partnered with Amazon and feel this move is a big win for Star Citizen and by extension everyone that has backed the project.

p.s. I wont be replying to this as it is Christmas and I am meant to be enjoying a bit of time off with my family (and playing some games - you may see me pop into a Star Marine or AC match or two!)

p.p.s Happy Holidays All!