@Great Argus to give a better idea of size, the interior space is a bit larger than the window (it goes up about as far as the top of the sign) and the tarsier is just above the top edge so can't be seen in the photo, but it is probably roughly the size of the food bowl which is visible, so the box is very small indeed. It may be lame however - in my review/species list (Ueno Zoo species list: February 2025 [Ueno Zoo]) I wrote "The tarsier in a tiny box was particularly distressing, although the angle of its leg suggests it may not be able to move well."
When I visited in January, I was allowed to visit Nocturnal House despite its closure for visitors and tarsiers were kept there in decent sized enclosure, maybe it is only temporary solution.