Total training for anesthesia is 4 years, but a prelim year is required. If you do a medicine year (either prelim or a switch from categorical) you will be eligible for 3 full years of subsidy because you can be board certified in IM in 3 years. Any time spent in residency after those 3 years, e.g., your last year of anesthesia, will be at one-half subsidy. If you did a transitional year, you would be eligible for 4 years because you can't be board certified in transitional medicine. This doesn't apply if you started out in a categorical anesthesia residency because they are categorical. See page 6 of the link.
"A number of specialty programs
require one or two years of prior
general training in another specialty
before receiving training in the specific
specialty; these include anesthesiology,
dermatology, pathology, radiology,
child neurology, and ophthalmology.
Prerequisite years of training can be
taken in a preliminary program in
another specialty (such as internal
medicine or general surgery), in a oneyear
transitional program, or in the
actual specialty if a first-year position is
offered. If the preliminary year or years
of training are taken in another
specialty, the initial residency period is
determined based on the training
required to become board eligible in the
preliminary specialty."
Will the program get less money if you leave a categorical IM instead of doing an IM prelim? No. But they will get less money than if you had done a prelim year in surgery, a transitional year, or started a categorical anesthesia program. Is this going to hurt you in the end. Probably not.