Disclosed herein are techniques for using a line-of-code behavior and relation model to determine software functionality changes. Techniques include identifying a first portion of executable code and a second portion of executable code; accessing a first line-of-code behavior and relation model representing execution of functions of the first portion of executable code; constructing, based on the second portion of executable code, a second line-of-code behavior and relation model representing execution of functions of the second portion of executable code; performing a functional differential comparison of the first line-of-code behavior and relation model to the second line-of-code behavior and relation model; determining, based on the functional differential comparison, a status of functional equivalence between the first portion of executable code and the code portion of executable code; and generating, based on the determined difference, a report identifying the status of functional equivalence.