Maybe a bit pedantic, but if you're streaming it, then you're still downloading portions of it, yah? Just not persisting the whole thing locally before viewing it.

Edit: Looks like this is a slight discrepancy between the HN title and the GitHub description.

Yes, I agree. I'm not persisting the WSI locally, which creates a smoother user experience. But I do need to transfer tiles from server to client. They are stored in an LRU cache and evicted if not used.