They’re out in 4.15 previews. If you have the source and are a programmer, the new audio renderer/mixer is in the AudioMixer module. Maybe should have called it AudioRenderer since I think people keep getting confused that this is like a mixing console sort of thing or some specific “mixing” feature. I mean, it technically is but it’s not precisely what it is and not what people mean when they say “mixer”. But most people know what a graphics renderer is, and this is basically the analogue of that for audio.
Anyway, the version in 4.15 is the version that we’re using with Robo Recall (at least as close as I could get it). It’s definitely still an experimental release and a use-at-your-own-risk sort of thing since it’s only used on one of our games and not ultra-vetted by QA, at least at the same level as the old audio engine since the old audio engine is A) used on lots and lots of games and our own internal Paragon/FN, etc, and B) is ultra-old so most of the glaring bugs have been hammered out (or are known) at this point.
I also am still finding and fixing bugs in the new renderer at a relatively high rate (although it’s been about 4 weeks on Robo Recall without any new issues popping up) so I’m not 100% confident in recommending new games use it yet. Definitely check it out and let me know if you find any problems.