Change of plane or change of materials requires caulk that will expand and contract with movement, not grout. Have them come back to fix it.

Agree, this joint needs flexible caulk, not grout.

I had the same issue. The tile dude grouted my backsplash tile to my quartz. Cracked in 3 months. My handyman removed it and laid a nice bead of caulk, but honestly, I could have done it myself had I been sure of the problem. I think this a common mistake.

Thanks for the response, that makes sense. I appreciate the help.

Yep, they're all correct. The other issue is your grout has shrunk, depressed a lot between tiles. Whoever grouted either mixed the grout incorrectly or didn't apply it properly. Not a lot to be done about that now, but I bet they didn't seal the grout either. You should seal it. It takes a couple of minutes, and dries overnight.

Oh no! Mine is grouted in the same place too. No cracks yet but I'm sure the first earthquake will fix that. :)

Don't wait for an earthquake, lharpie. It's easy enough to fix and no reason to wait until it's falling bit by bit onto the counter.

Sometimes they don't crack and some grouts are crack resistant. When caulking, make sure to match sanded or unsanded. You can send a chip to a company called Color Rite to get a match to the existing grout. Buying the grout manufacturer's caulk does not necessarily match and hasn't yet in my experience. They can be way off.

Yes but taking out the grout sounds much easier once there is cracking. For now it is doing its job so it's hard to get excited about removing it!

After the tops are installed level, it's best to temporarily install a continuous shim the thickness of the grout lines along the wall. Install the tile to the wall on top of the shim and grout. Pull the shim and pump the perfect void full of color matched silicone caulk as the last step.

The builder will be coming by to look at it and see what can be done at this point.

Tilers often want to grout those joints and deal with a callback later if it cracks instead of making another trip during install to caulk. The joint needs to be cleaned out and caulked. There is no problem doing something like that at this point. Well, I guess you have to worry about them chipping the tile, dinging the cabinets, marring the floor ...