Difference between "I have got" and "I have gotten"
In general, "have got" is the present perfect form of "to get" in UK English, while "have gotten" is the US English version.
However, even in US English, "have got" is used in certain instances, namely to mean present tense have (in the sense of possession, or to mean must):
- I have got a lot of friends. (=I have a lot of friends)
- I have got to go now. (=I have to go now/I must go now)
Gotten is probably the most distinctive of all the AmE/BrE grammatical differences, but British people who try to use it often get it wrong.
It is not simply an alternative for have got. Gotten is used in such contexts as
They've gotten a new boat. (= obtain)
They've gotten interested. (= become)
He's gotten off the chair. (= moved)
But it is not used in the sense of possession (= have). AmE does not allow
*I've gotten the answer.
*I've gotten plenty.
but uses I've got as in informal BrE. The availability of gotten does however mean that AmE can make such distinctions as the following:
They've got to leave (they must leave)
They've gotten to leave (they've managed to leave).
From the The Cambridge Encyclopedia of English Language.