The Microsoft Surface Book and Surface Pro 4 launched back in October, and Ryan published a review of them in December. He didn't really make reference to it, but the highest-end model of each were unavailable until a later date. As it turns out, that time is roughly now. I say “roughly” because, while Microsoft has launched the devices, Amazon's landing page doesn't list them, and searching for the product directly shows a price tag of just under $10,000. I assume Amazon hasn't pushed the appropriate buttons yet.
The only real improvement that you will see, versus the second-highest SKU, is a jump in SSD capacity from 512GB to 1TB. This extra storage will cost roughly 1$/GB, but this is also a very fast NVMe SSD. If 512GB was too small, and you were holding out for availability of the 1TB model, then your wait should (basically) be over.
Although, since you waited this long, you might want to hold off a little longer. Microsoft is supposed to be correcting (some say) severe issues with upcoming firmware. You may want to see whether the problems are solved before dropping two-and-a-half to three grand.