Recurrent training

[leonard17F]

All,

For an FAA license:
I was typed on but have not flown a certain type (A) of A/C for around 4 years. I am currently flying on another type (B) of A/C. (Same class of Biz jets)
What would I need to do to fly Type A again: a recurrent only (1 week, 2-3 sim sessions)? of a full initial (3 weeks, 8 sims) ?
(I am talking PIC here).
Thanks a million for your helpful replies !

[411A]

A proficiency check only, is required, under 14CFR91.
14CFR135 would be different.

[leonard17F]

Thanks !
Now what if I had not flown in the past 4 years, would I need to perform a full recurrent or only a checkride?