This is why you caulk, not grout, plane chnges.

Thank you, Joseph! We just got this as is. Is this something we should point to builder while we have 1 year warranty? How to bring this matter in a correct way?

I'm also reading https://www.pjfitz.com/blog/bath/grout-vs-caulk-for-bathroom-tiles/

"Caulk is flexible, so it can be used to adhere two different materials together (such as tile and glass). Grout, on the other hand, won’t adhere to the surface of materials; it needs a crevice to sit in.

Because caulk can shrink over time, it shouldn’t be used in large projects.

Grout dries firm and strong, so it helps protect the edges and corners of tiles from cracking or breaking."

Any and all changes in plane are required to be silicone caulk, not grout per TCNA standards for this exact reasoning.

It doesn't look like anything to worry about though. Yeah, that cracked grout should be replaced with caulk, but structurally it's nothing catastrophic.

I don't think there is any reason you can't use it as is--it's just cosmetic.

It won't leak? Would it?

OP - whether your shower leaks or not depends on the waterproofing under the tile and grout and not on the grout. Just get the contractor to do what he should have done from the start and replace the grout with silicone at the change of plane.

And make sure that all of the other showers have caulk, not grout, at all the plane changes.

It won't leak? Would it?

If your shower was properly waterproofed BEFORE the tile and grout were put on, you could shower in it without tile and grout and it wouldn't leak! Tile and grout are just the bling and have nothing to do with how the foundation was made.

^ Had a lady shower in orange Kerdi for two weeks when I went on vacation.

Ask your builder how he plans to fix it. He should say remove grout and replace with caulk...if he wants to just regrout you are in trouble as that might indicate he does not know how to build a shower. The cracks look quite wide and do suggest movement, but that should not happen in a well built shower.

They also sell the best of both worlds! Grouter sealer. It's basically caulking and grout in one tube. Daltile sells it. Other places too probably. They can give you the name of their product.

If you want peace of mind? Hire an independent plumber. Ask them to insert a cherne test plug down BELOW the drain flange and fill it up to the curb let it sit for a day see what comes:)

Sure you could do it yourself but you want the plumbers assessment and his flood insurance.....

Why would an independent plumber test another contractors poor work at the expense of his insurance?

The cracks are fairly wide already. Did you also noticed different „elevations“ on both sides of the crack?

If so, I would be definitely concerned 😧 because there is a chance that your waterproofing membrane underneath the tiles is compromised.

Some waterproofing membranes can be "stretched" up to 1/8 of an inch, however, if the surfaces on each side of the crack have different elevations, the 1/8“ might be already exceeded.