Is there a particular model of sled that is approved for use during the new Army Combat Fitness Test (ACFT, formerly the ACRT)?

Great idea I would reach out to a recruiter they have most of the equipment for the events.

There is a specific model and the NSN will be published soon in the equipment list. It's due to be published any day.

https://mwi.usma.edu/good-bad-armys-new-physical-fitness-test/

Good info

Currently, as of last night, the DoD defense budget has been passed (Veto overridden from President Trump), which in it included a request to halt the ACFT adaptation in order to investigate failure rates of the current ACFT events. I only mention this because TRADOC (EDIT: technically any MACOM) may be in a pickle for awhile as no one can technically force a record ACFT, and the Army overall doesn't have a PT test of record at this time. This is to ease any concern over passing, but shouldn't be an excuse to not be in proper shape! (mostly running, and push ups....)

Now for the sled portion... there is a bit of confusion about the actual requirements as they have changed many times throughout the last 3-4 years of testing. At this time, the latest equipment manual from an Army source states this:

NOMENCLATURE: NYLON SLED (WITH PULL STRAP)
A. DESCRIPTION: 1 X PER LANE. THE NYLON SLED CAN BE DRAGGED ON MULTIPLE SURFACES (GRASS AND TURF).
THE SLED CAN HANDLE UP TO FOUR 45LB PLATES AND IS CONSIDERABLY LIGHTER THAN THE TRADITIONAL METAL DRAGGING SLED.
THE SLED SHOULD NOT BE USED ON CONCRETE, ASPHALT, OR ANY ROUGH TEXTURED SURFACE.
USE OF SLED ON AGGRESSIVE SURFACES CONCRETE, ASPHALT, OR ANY ROUGH TEXTURED SURFACE WILL SIGNIFICANTLY SHORTEN THE LIFESPAN OF THE SLED.
THE NYLON SLED CAN BE ROLLED UP FOR STORAGE.

B. SPECIFICATION:1) MADE OF THICK HEAVY DUTY NYLON.2) SIZE STANDARD IS 22” (LENGTH) BY 19.5” (WIDTH).2) CAN HANDLE UP TO FOUR 45LB PLATES.
WEIGHT STANDARD IS 90LBS (2 X 45LB PLATES).3) MUST INCLUDE PULL 92”STRAP WITH HANDLE ON BOTH ENDS.4) NYLON SLED COLOR IS NON-SPECIFIC.

C. USACIMT PROCUREMENT RECOMMENDATION: PRESENTLY, METAL SLEDS ARE NOT AUTHORIZED FOR USE IN THE ACFT. NYLON SLED WITH STRAPS IS ONLY AUTHORIZED SLED FOR RECORD TESTING. STRONGLY RECOMMEND PURCHASING SLEDS AND PULL STRAP AS A UNIT.

This is from the ACFT website here: https://www.army.mil/e2/downloads/rv7/acft/acft_equipment_list_final.pdf
This STATES it's the final revision of the equipment, but from our MFT-certified Soldiers, there is talk about using different types of sleds for those that do not have grass or turf to use for the nylon sleds, but nothing has been properly put out (at least through my chain of command).

I would definitely stick with a nylon-based sled and use grass or turf as much as possible. There may be changes in the future but just starting the sprint-drag-carry will benefit you more than getting the "right" equipment for a testing system the Army is still modifying and adjusting with.