From the Google guys https://twitter.com/tjohns/status/614310159922233344

Looks like 4K is what they state for a possible future lenght ... so we could do something, like ignoreing that - but this leads to bugs (similar to AGPUSH-1370).

As a matter of fact the stated 250 is not yet true (in AGPUSH-1370 we got a 153 long token)