H3 says a6 and h6 are best moves in QGD!?

According to H3Pro at 25 depth, a6 h6 and c5 are top 3 moves followed by Be7 in this opening:

Whereas according to chess databeses, h6 has only been played once at 2700 level by Shirov vs Kramnik in 2007. And a6 has never been played at this level, despite being the best move by the best engine!!!

A possible new novelty?

Never trust engines for openings. 

This exactly !!

Im not saying it is a better move, but it is clearly a viable alternative with no flaws. Certainly worth to be played and analyzed more.

Although a6 and h6 are played later in this opening, why not play it early and you might put off your opponent.

According to H3Pro at the 25th floor of any building, the top 3 moves are Jump out the Window, Dive Head first out the window, and Sit in the Window ledge facing inward and being pushed from the ledge, followed by going inside and taking the stairs down a distant 4th.

You going to take that advice too?

If H3Pro was the best sky diver in the world, I might were it not for my fear of heights :p

It seems that your line of reasoning about 4. ...a6 is catching on at the high GM levels. If you check the position in chesstempo's database for games where both players were 2600+ , you'll find 18 examples as of today. There is one example from 1925 and another from 1949, and then 16 after 2016, so my guess is that this is an engine-inspired novelty.