"beatnik"--coined by Herb Caen?

[Laurence Horn]

That claim, made tonight on Jeopardy, is supported by various web
sites (the idea being that the San Francisco Chronicle columnist came
up with the term in a 1958 column, of course as a blend of "beat
(generation)" and "sputnik"), but does not appear in the OED entry
for the word.  The RHHDAS does endorse the Herb Caen coinage, though.
Are any antedates available, or is this an rare actual instance of a
verifiable and attested coinage?

larry