Yes, it will be an issue. Composite materials expand and contract too. Just less than solid wood.

What others said, you have to use trim pieces at the corners and you have to leave a 1/4" expansion gap between wall and ceiling, and pretty much 1/4" gap must be provided no matter what the panel meets, i.e floor, wall, ceiling, etc. This space allows the wood to expand and contract and the gap is always covered by trim.

Thanks all. Just curious, how does one get this kinda of look then? It looks seamless. If I trim it down with a 1/16 inch gap on each side and caulk, do you think this would work?

This is a beautiful look, the only thing is missing is a few more pictures after seasonal changes unless they did the ceiling 1st and ran everything else afterward, other than that there will always be separation at the transition point when the temperature starts to change.

Just use low profile molding or a narrow cove molding, it will add some detail and you will not see any separation when expansion and contraction occur especially at the ceiling level, because the temperature there always fluctuates unless you don't mind climbing up there and maintaining.

Good luck

You get that kind of look by taking the photos the same day the project is finished!

You need more than 1/16 for an expansion gap. You need at least 1/4. You also do not caulk it. It needs to expand, not be caulked in place. It requires a moulding at the edges.