Yes, this is due to Intel participation. From their post on Steam forum:
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Vertigo Games [developer] 17 hours ago
Single Player Horde Mode & Apocalyptic Mode
These are two game modes that we have not focused on previously.
Working with Intel allowed us to create even more content than we originally planned, including these modes and the physics systems in the game, making Arizona Sunshine one of the richest VR experiences possible. We want to give 5th, 6th and 7th gen Intel® Core™ i7 owners first glimpse into these additional modes, but they’ll be available March 6, 2017 to everyone who owns the game.
Single Player Horde Mode is as you would expect, a single player experience in Horde Mode.
Apocalyptic Mode is the highest level of difficulty in the campaign. Its features include:
• Only one weapon (handgun)
• Very limited ammo
• No checkpoints - you die and go back to the start of the game
• One hit death
Completing this is tied to an achievement that will result in an award of a golden desert eagle pistol for use in multiplayer and future apocalyptic sessions. The gun will be added in a future update.