It's not I'm afraid - the 'extended cut' I assume you're talking about is the Chinese Cut (130 minutes) that was debuted for the Asian market. The second cut was 7 minutes shorter and shown at the BIFF last year. The third US cut (overseen by The Weinstein Company) is a further 15 minutes shorter (so 22 minutes shorter than the first cut) and that is the version we are getting,
as confirmed by the BBFC.
Here's Wong Kar-wai himself talking about this third cut, and how it shouldn't be seen as an 'inferior' cut like many critics and journalists have reported since:
I personally thought the 108 minute was excellent. Of course I'd like to see the other two cuts one day (either really, as I'm assuming the 123 minute cut is similiar to the 130 minute 'original' cut), but I'm still happy with this one. As he said himself he actually got to
add footage that got removed the first time around, so see it more as an alternative cut to the original. Compared it with Wong's contemporary John Woo, whose Chinese epic Red Cliff (incidentally also starring Tony Leung) was cut by 120 minutes - from 288 minutes to 148. The cuts to The Grandmaster are in no way as drastic as that and it seems have been over exaggerated by the western press, festering in the period of anticipation for its eventual release over here.
It's different to the recent Snowpiercer fiasco which do I do think the US cut is a little clunky (but still tells the story brilliant) and would like to see the original cut in that case. But the fact is these films seem to be entering the UK market via the Weinsteins, so we'll have to bite our lip and make do for the time being. Sure, maybe one day we'll see a release of a different cut but there's no need to wait - this is still a beautiful film.