This study investigates the thermal stability of Ti₃C₂Tₓ MXene monoflakes and multiflakes in air, revealing that monoflakes exhibit exceptional stability up to 600°C, while multiflakes oxidize readily at 300°C. The oxidation of multiflakes is attributed to confined water between stacked flakes, which has higher removal energy than surface water and persists at higher temperatures. Vacuum annealing at 600°C effectively removes this confined water, significantly improving the thermal stability of multiflakes, allowing them to withstand 600°C in air without oxidation. Density functional theory calculations confirm that confined water has higher removal energy than surface water, making it a key factor in the oxidation of stacked flakes. The study provides insights into the role of confined water in MXene oxidation and offers guidelines for vacuum annealing to enhance the stability of multiflake films. These findings highlight the importance of controlling water content in MXene films for high-temperature applications and demonstrate the potential of stable monoflakes for use in extreme thermal environments.This study investigates the thermal stability of Ti₃C₂Tₓ MXene monoflakes and multiflakes in air, revealing that monoflakes exhibit exceptional stability up to 600°C, while multiflakes oxidize readily at 300°C. The oxidation of multiflakes is attributed to confined water between stacked flakes, which has higher removal energy than surface water and persists at higher temperatures. Vacuum annealing at 600°C effectively removes this confined water, significantly improving the thermal stability of multiflakes, allowing them to withstand 600°C in air without oxidation. Density functional theory calculations confirm that confined water has higher removal energy than surface water, making it a key factor in the oxidation of stacked flakes. The study provides insights into the role of confined water in MXene oxidation and offers guidelines for vacuum annealing to enhance the stability of multiflake films. These findings highlight the importance of controlling water content in MXene films for high-temperature applications and demonstrate the potential of stable monoflakes for use in extreme thermal environments.