- This house has got six bedrooms.
- This house has gotten six bedrooms.
#1 is correct. Is #2 acceptable in American English?
If what you intend to say is that the house “has” or “possesses” six bedrooms, you have to use sentence 1 – in both BE and AmE.
This house has got six bedrooms. = This house has six bedrooms.
If you said “This house has gotten six bedrooms”, that would sound as though the house had received six bedrooms somehow. Maybe six bedrooms had been added, for example. So, sentence 2 is not only a pretty unlikely sentence, but it also does not mean the same thing as sentence 1.
“Has gotten” is used in AmE to mean “has received” or “has become”, for example.
- He has gotten six job offers this week. (has recieved)
- It has gotten considerably colder in the last few days. (has become)