The VLTI can operate in three possible configurations, according to the telescopes array, that is the set of telescopes selected for the observation run:

• VLTI Main Array (VIMA): configuration of 2 up to 4 UTs. The remaining UTs are available for standalone operation.
• VLTI Sub-Array (VISA): configuration of 2 up to 8 ATs. This configuration is completely independent from the UTs.
• Hybrid: heterogeneous configuration of 2 up to 8 telescopes selected among UTs and ATs. Every combination must be supported.