Here is an overview of the average performance at open test. But we shall not extrapolate too fast… Presumably the most difficult will be from 98% to 99%, and even worse from 99% to 100% (if attainable…). It could even be extremely difficult to pass from 99.00% to 99.10%… And it may even take two years to pass from 97% to 98%. Who knows?
Now an open question that is lurking is the following: how hard will it be to pass from 98% to near 100%? To simplify matters and to put it in a sharper form, we can formulate it as follows: how hard will it be to pass from 99% to near 100%? Call it the last percent problem. It seems such an ability would at least require multi-language translation capability. But it could even require full-featured AI (not limited to machine translation). To put it more clearly: will near human quality translation require full-featured AI?