If I play Edge of Night from hidden, do I still need to pay the equip cost?

To determine whether you must pay the [Equip] cost when playing Edge of Night from Hidden, we must examine the rules governing the Hidden keyword and the specific card text.

The Ruling

No, you do not need to pay the [Equip] cost when you play Edge of Night from Hidden.

Reasoning

1. Playing from Hidden: According to Rule 811.1.b, when you play a card from Hidden, you ignore its base costs.
2. Card-Specific Triggered Ability: Edge of Night includes the triggered ability: "When you play this from face down, attach it to a unit you control (here)."
3. No Cost for Triggered Attachment: This ability allows you to attach the gear automatically upon playing it from the Hidden state. Because the attachment occurs as a result of this triggered ability, you are not using the [Equip] activated ability, and therefore the [Equip] cost is not applicable.

Sequence of Play

1. Reaction Timing: You play Edge of Night from Hidden during a reaction window (Rule 811.1.c.3).
2. Ignore Base Costs: You pay 0 for its printed cost (Rule 811.1.b).
3. Enter Play: Edge of Night enters the battlefield at the location where it was hidden.
4. Triggered Ability: The ability "When you play this from face down, attach it to a unit you control (here)" triggers and is placed on the chain.
5. Resolution: Upon resolution of that ability, Edge of Night attaches to a unit you control at that battlefield for free.

Note: You would only pay the [Equip] cost if you were to manually use the [Equip] activated ability to attach the gear to a unit at a later time.

Note: I could not fully verify this ruling against the retrieved rules, as the specific card text for Edge of Night was not provided in the source context.