103,000 were in the fourth quarter following the announcement of Valve's flagship VR game, Half-Life: Alyx, which was made free to Index owners.

[12] The headset features dual 1440 x 1600 LCDs with full RGB per pixel and ultra-low persistence global backlight illumination (0.330 ms at 144 Hz).

The headset and controllers both use lighthouse tracking systems, while retaining full compatibility with all previous HTC Vive base stations,[13] using SteamVR.

These base stations are small, rectangular units placed around the room that emit non-visible infrared light and laser patterns.

In addition to the base stations, the Index’s headset and controllers feature Inertial Measurement Units (IMUs) that provide rapid updates on movement and orientation.

The Lighthouse system compensates for this drift by using the base stations’ lasers to provide a precise positional reference, integrating this data with the IMU information to maintain accurate tracking even during fast movements.

[19] The Index includes "a pair of ultra near-field, full-range, off-ear (extra-aural) headphones",[20] which use Balanced Mode Radiator (BMR) drivers to produce accurate and low-frequency sounds.