From the update notes:

• Headdress has been removed: We learned that headdresses are mostly worn for ceremonial events vs battles or combat
• Hair: Thunder now has a traditional warrior style pompadour hairstyle, based off historical photos
• Added arm braces and a belt with traditional Nez Perce beadwork in the common color palette of pink & green with geometric pattern
• Buckskin pants with the same traditional Nez Perce beadwork in pink & green with geometric pattern
• Traditional moccasins: Worn for more agile combat and handcrafted from raw materials
• Traditional metal-work axes

I think this is an awesome update, and a great gesture from Microsoft and Iron Galaxy. The new optional skin looks badass, and the pompadour is beyond cool. As expected, some people are losing their minds over the fact that Iron Galaxy took the time to make a "fictional" character a bit more accurate, but eh. I hope more developers try to delve into the sources of their characters more in the future as well - it leads to more unique and interesting characters, in my opinion! I had no idea that the popadour was a traditional warrior hair style for the Nez Perce.

Honestly, the redesign looks way more badass than the original one

Yeah I def dig the new design. Is this free for all players? edit: just noticed free in the title

Thunder's track Hinnamatoom will always be my go to music when I need to get hyped.

Really dig the do.

I really appreciate more acurate details, especially in character design. More often than not reality is far more interesting than the imagined. This is one of that instances. That pompadour rocks but its even more amazing that it was and actual thing.

This video kind of makes me wonder if those Nez Perce folks knew that they weren't redesigning Thunder's default costume, and that this would be a third option under the original one and... this:

It's still a really cool gesture and it's probably more than Capcom or NRS have done with their own questionable Native American charaters, but it kind of bums me out to see them talk about the mis-steps Double Helix made with their 2013 redesign when that's still how Thunder is represented in 99% of KI's art.

Then again, maybe a KI sequel is in development right now, and they'll use this redesign as his default costume in that. Who's to say?