The Leclerc Séries XXI is the third variant of the Leclerc main battle tank family. It has significant enhancements and improvements over its predecessor, the Leclerc Séries 2. The turret now has a new composite front armour package that includes titanium. Turret bustle composite armour has been replaced with lighter explosive reactive armour. Turret storage bins are also being redesigned to allow for potentially larger add-on armour packages, increasing versatility and adaptability. The Leclerc Séries XXI also has a hunter-killer capability thanks to the HL 120 panoramic sight, which contains a laser rangefinder and Iris thermal imaging equipment. Finally, the tank is now equipped with a friend or foe identification indicator.

Introduced in Update "Winged Lions", the Leclerc Séries XXI is well-protected overall, with an effective configuration that results in good survivability. The frontal turret of the Leclerc Séries XXI is particularly well protected by modular composite armour, which combines strong metals, semi-reactive, and ceramic layers to protect against even the most powerful tank ammunition. The modification also involves the inclusion of extra armour beneath the gunner's sight, lowering the likelihood of the gunner being knocked out during conflicts. The Leclerc Séries XXI also has a new HL 120 panoramic sight for the commander, as well as thermal imaging equipment and a laser rangefinder, bringing hunter-killer capability to the Leclerc Séries XXI.