With every new generation of graphics cards, NVIDIA and ATI advertise with all kinds of neat features.

What I'm curious about is how as a developer I can take advantage of these features. For example the new GTX900's prominently advertise Voxel Global Illumination, and MFAA while ATI advertises improved ansiotropic filtering and partially resident textures for the R9 series.

I've searched the developer sections of each GPU maker's websites and they have lots of great samples for other algorithms but it seems the ones they advertise are missing?

This link says:

Currently, this tech is being built for popular game engines like Unreal Engine 4, and will be available for game developers by the end of the year.

So that's probably out of reach for now.

This video at around 1:55 says MFAA can be enabled in the NVIDIA control panel so it might not be something you can require of your game.

I didn't look into ATI's improved anisotropic filtering in great detail, but I suspect it's something that is had 'for free'. That is, if your game uses anisotropic filtering then someone with an R9 will see improvements. I also found that partially resident textures are called "tiled resources" in DirectX 11.2. I found this link which discusses it.

For example the new GTX900's prominently advertise Voxel Global Illumination

Sounds like middleware they provide rather than a NV_voxel_global_illumination extension and glVoxelGlobalIllumination(true) call pair.

They had a bunch of specific effects and things in Assassin's Creed too. nVidia showcased a tech demo of some water rendering, which later made an appearance in Assasin's Creed, via "nVidia Gameworks" program. Much like TWIMTBP program, except this deals with concrete features as middleware it seems, like that "APEX turbulence" thing.

NVidia's Voxel Global Illumination isn't a GPU feature, it's a middleware library that you can license (for $$$$$$) on their GameWorks page.

Likewise, MFAA is a shader they'll sell you for cash...
Their marketing team is pretty disingenuous these days.

Internally, that Voxel GI library depends on partially resident textures / tiled resources.
In GL there's an extension, and in D3D you need to create an 11.1 device.
Technically, it would work fine on AMD cards too...

AMD actually beat NVidia to support tiled resources tier 2, so NVidia's marketing team is going nuts.

Yeah, the thing to keep in mind is that many/most AAA games these days are piles of middleware. GameWorks, Enlighten, Morpheme, Substance, PopcornFX, Umbra, SpeedTree, Havok, Scaleform, Wwise, Bink, and many dozens of others, not to mention proprietary content tools or tool plugins.

For cutting-edge hardware features, these are often either proprietary middleware packages /or/ just a secret NDA set of documentation that only the big high-dollar AAA games get access to (often they come coupled with expensive support contracts that gets one of the hardware company's engineers on premises helping you integrate the feature into the game).