The beta channel is once again open and, as usual, Galaxy only.

Aside from the fourth DLC Kingdom's End, it comes with a shipload of new things and fixes but also a slew of new bugs due to the reworked engine.

http://forum.egosoft.com/viewforum.php?f=192

By the looks of the state the game is in, it will be in beta phase for several weeks.

Beta v4 out now. Based on the changelog, it might be playable now. I would not know as you must have the Galaxy client in order to play the beta.

My personal guess is that this is either the last or second to last version where the game supports processors without SSE4.1. I doubt the v6.0 proper will support those old processors. Time to look at getting one of AMD's upcoming (beginning of March and a couple of months later for the smallest model) 3D cache processors or an Intel 13600 or better. Either choice should be paired with better than SPD RAM, in other words, use overclocked RAM.

Quoting the changelog:
"[Beta 4] Removed requirement for CPU to include SSE4.1 support (experimental change, may need to be reversed)."

I seriously doubt it's an issue now, not unless your CPU is like 20 years old which would make it impossible to run this game anyways. Anything like Core 2 duo or later already had SSE 4.1, so it's been around for almost 2 decades by now.

AMD's Phenom II series was the last I know of that did not have support for it. Fairly capable processors back in 2009 and at some point there were even a couple of six core models, true six cores unlike the processors AMD made after Phenom II but before Ryzen. I suspect you would need to overclock it heavily in order to make it usable in this game. I ran my own with a 15% overclock and the whateveritwascalled bus with a 20% overclock. Still, I would never want to even try running the game on that.