This Colt Hammerless Experimental Prototype .380ACP was a toolroom example and was estimated to be manufactured according to the letter ~1946. The factory records indicate that this firearm was kept by the Colt company in the Engineering Vault. As of this writing it's unsure how this particular pistol made it out or exactly when.
This particular pistol "GX2501-1 was made up from a scrapped Model M" as discussed on page 35 of "The Colt Pocket Hammerless Automatic Pistols" by John M. Brunner.
The consecutive prototype, "GX2501-2," is pictured and discussed on pages 34-35 and listed as "an attempt to develop a postwar .380 pistol to replace the Model M." That example is listed as from the Connecticut State Library collection.
Brunner notes that three variations were produced, and two remained in the Colt Engineering Reference Collection at the time of his writing. The first drawing for this model was dated 1946, and Brunner notes the second prototype was sent to the Engineering Department on February 2, 1953, which provides a rough time frame for when this pistol was manufactured. It has pistol has a fixed blade front sight, dovetailed notch rear sight, "GX 2501-1" on the right side of the frame, manual thumb, safety short grip safety, magazine disconnect safety, serrated grips with nickel Colt medallions, and no visible markings aside from the serial number.