To most of the world, the Jay-Z song that hit the Web Wednesday night is brand new. Yet fanatical Jay buffs like, er, myself, have been waiting for “Ain’t I” for almost a full year — ever since a song by that name was mentioned in EW’s March 2007 profile of Timbaland. Back then, he was working on “Ain’t I” for Timbaland’s in-progress Shock Value. Writer Ethan Brown was in the Miami studio where Tim stayed up all night waiting for the rapper to finish recording his verses in New York; in the end, they missed the label deadline for Shock Value by mere hours. I know you can’t rush genius, but considering how awesome Tim and Jay’s many collaborations had been in the past — “Big Pimpin'”! “Jigga What, Jigga Who”! “Lobster and Scrimp,” people! (NSFW lyrics) — I was slightly crushed that “Ain’t I” never made it out.

Well, “Ain’t I” is everywhere now, thanks to a DJ Clue mixtape, and it is so worth the wait. (Check it out below; some lyrics NSFW.) The beat is one of the better freaked-out Martian bounces Tim’s conjured up in recent years — it evolves through something like 3 or 4 separate mind-twisting movements — and Jay spits some extra-sharp braggadocio. (Notable themes, in addition to Hovie’s own messianic status in the rap world, include modern art: “Warhols on my hall’s wall/I got Basquiats in the lobby of my spot.” Either he’s taken up residence at MoMA, or that’s one well-decorated pad.) The unofficial YouTube dude below uploaded “Ain’t I” with a pic of a throwback-jersey-wearing Jay circa 1999 — appropriate, since this track is an excellently show-offy excursion to the territory Jay and Tim were working back then.

One other thing: How come DJ Clue keeps shouting the highly intriguing phrase “Blueprint 3” in the background? Could Jay possibly be back in the studio now, recording a threequel to his Blueprint and Blueprint 2 albums? That’s what some online busybodies are whispering, of course; his publicist would only say that “Ain’t I” is “an old song” when I asked if it was part of any larger project. So who knows what’s next for the former Def Jam CEO? In the meantime, I’ll be bumping this track indefinitely.

addCredit(“Jay-Z: Kevin Mazur/”)