A new build is available for Windows 10 at the Insider Fast update level. This one is numbered 11082, and it is the first one on the “Redstone” track. Users will probably not notice any changes, beyond the bugs, because the modifications are all under-the-hood. They are working on the core of the operating system, called “OneCore,” to restructure it better for the wide variety of hardware that it's designed for.
This raises the question: Why now? It's odd that they would release a public preview that seemingly adds nothing, just before the holidays when the engineers will be unavailable to fix it. That feels like replacing the first floor of a building from wood to maybe-not-quite-set concrete, then hopping on a plane for a few weeks. Of course, this is not a bad thing. This is what some Insiders want to experience, and those who don't can drop down to Slow (or leave Insider).
Also, Microsoft sort-of explained why they did this. First, they intend to get down to business on features and upgrades in January. Basically, they structured their work such that pre-Holiday tasks built the infrastructure for post-Holiday creations (as I mentioned in the first paragraph). Big development tasks are often done on branches of a canonical product that are merged when complete. Merging a branch back into the trunk is easier when the trunk is designed more modularly, etc. In that context, it makes sense to see how it reacts in a large sample of configurations just before you start pushing big feature payloads into it. The second explanation is that Microsoft intends to speed up Insider previews in general.
If you're interested, WinBeta has a video “walking through” the features, although they basically just read the announcement. They also checked to see whether Microsoft Edge changed to add extensions, and it didn't.
A list of known issues is also available in the Insider Hub app post. Basically, Language packs and "Features on Demand" will not install. File progress dialogues will not show (even though the actual copy / move / delete will work without issue). Finally, some default apps will be incorrectly reset.
It is available through Windows Update for Fast Insiders.