Google merged the "pipit" and "passport" device projects because they eventually converged into a single device, which continued to be called "pipit3." While they were different projects at some point, it seems that combining them allowed for a more focused development effort and a unified vision for the final product.
The "pipit" prototype had a slightly smaller outer display at 66 x 128mm compared to the Pixel Fold's 67 x 130mm. The resolution also differed slightly at 1,080 x 2,100 pixels compared to the Pixel Fold's 1,080 x 2,092. The refresh rate ranged from 10 Hz to 120 Hz.
"Pipit" was intended to run Android 12L, which was Google's large screen-optimized version of Android. It would have been one of the first devices to run this software, had it not been canceled.