I think that's either not a guitar, or quite possibly it's a combined slide and ebow to get that real glissando-sustain sound. The really smooth note transitions make me think it's a slide and the complete lack of attack on any of the notes is making me think ebow.

Either that or it's not a guitar at all
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”

I think it is what Zaphod mentioned, a guitar with a slide and ebow being used. That is of course pure speculation, but i think that is what it is.
Fusion and jazz musician, a fan of most music.

Quote by Guthrie Govan
“If you steal from one person it's theft, and if you steal from lots of people it's research”

Quote by Chick Corea
"Only play what you hear. If you don't hear anything, don't play anything."
If it's a guitar, he might be using an e-bow? Probably has a heavy dose of reverb added to it. That's my guess. Otherwise, maybe its just a synth?

BTW, the last time I checked, e-bows run for about $100... but that was like 7 years ago.
-Andrew H
band: syncopated groove punch
I sold my Ebow about 6 months ago
Thanks for suggestions, keep them coming!
Gotta be a synth.

Here's a live version, Mayer never touches an Ebow, finger picks the whole thing. They don't show the keyboard player during that section, but the part is there. Mayer is still finger picking...

Hmmm...I wonder what this button does...
I watched that video too but I'm guessing the drummer is playing to a click track with backing playing for that part, there's a few sounds that they don't play that you can hear on the original. The improv after it I guess is to stop it feeling sterile because they're playing to a click, that and the fact the original fades out. But that's a guess.