You know what... I think it just might be... a variant of it at least. To me, there are a few details that are completely different to the RA617H.
--My observations--
- The manifold tubes are larger in diameter most obviously, their shape is a little bit more extravagant (one of the runners swings up past the cam cover), and they're individually wrapped as opposed to being bag wrapped together. This also is in line with Honda saying at pre season testing that Toro Rosso allowed them the extra room to modify the exhaust manifold, McLaren allegedly would not give up the real estate.
- The air intake into the compressor is also slightly larger in diameter for the whole length of it and it has a much softer curve into the compressor, previously it was flattened from top to bottom and a very sharp entry into the compressor (again, presumably to save space in the McLaren). There's also a new breather hose off of it as well that is absent on the 617.
- Oil Tank looks like a slightly different shape, maybe a tad larger, especially the section around the compressor, it's no longer visible, on the RA617H, the compressor was visible from side on.
- Wastegate looks largely the same, coating/shielding looks like a different material, but nothing too drastic
But yeah there are a few notable changes, in my opinion, obviously open to being corrected but I'm inclined to believe thats the first real photo of the RA618H!