Most of the "top tier" hackers responsible for past rounds of jailbreaks (iOS6 & iOS7) may have their phones jailbroken on iOS7.1.x
But those jailbreaks are held to preserve the exploits and will never see the light of day for public release.
Stefen Esser is very talented, doesn't surprise me in the least he has a working jailbreak. That said, there may be others also but they don't advertise it otherwise their Twitter "hate mail" goes ballistic from those demanding a release.
Keep in mind also, the process he and others use to get that jailbreak may be so technical none of us could possibly perform it for ourselves.
Update: Just as I believed, other known "top tier" hackers have their own jailbreaks -->
https://twitter.com/winocm/status/467838845866606592