The advanced X-wing fighter, also known as heavy X-wing starfighter, was a heavy variant of the T-65 X-wing starfighter, developed as a result of the success of the Heavy '95.
The Advanced X-wing was developed by engineers who, because of their allegiance to the Rebel Alliance, were forced to adopt a "develop more with less" policy, demonstrating the engineers' innovation. Likewise, because of this policy, the Rebel engineers often concentrated on making minute but consequential changes to their fighters.
The Advanced X-wing's development was owed largely to the success of the Heavy '95, a heavy variant of the Z-95 Headhunter, as the engineers realized that wider bodies were good improvements to various concerns of starship performance. In large part because of this, the Advanced X-wing was supplied with similar modifications to its hull as the Heavy '95 before finalizing the latter fighter design. The improved heat handling and increased mass capacity made the Advanced X-wing a better choice for X-wing pilots.
After the Battle of Yavin, several advanced X-wing starfighters were awarded to Rebel pilots for escorting and protecting representatives of the Civilian Protection Guild on Kashyyyk.
As part of the New Republic, a squadron of advanced X-wings participated in the Liberation of Coruscant in 7 ABY.
Advanced X-wings in Star Wars: Galactic Battlegrounds.