History of Arc Threat

Arc Threat is a Lost Sector modifier that raises incoming Void damage by 25%, so Void-resistant armor and mods are the main defensive focus while it is active.

Where it appears

The modifier is listed on the Bay of Drowned Wishes Lost Sector in the Dreaming City, where Yirksii, Subversive Chieftain is the boss. A similar modifier, Void Threat, appears on Exodus Garden 2A in The Divide with the same 25% increase to incoming Void damage.

Lost Sector modifiers rotate, so check the current rotation before a run.