Quick definition
An options Greek measuring sensitivity to changes in implied volatility. High Vega means the option price is heavily influenced by volatility changes.
Where vega bites
Vega is highest for at-the-money options with the most time to expiration — long-dated ATM straddles are essentially pure-vega bets. Vega is lowest for short-dated OTM options. This is why an earnings IV-crush can vaporize a long straddle overnight even when the stock moves in the predicted direction: the gain from delta is dwarfed by the loss from vega collapsing.
Long vs short vega
Premium buyers are long vega and benefit from IV expansion. Premium sellers are short vega and benefit from IV contraction. A high IV Rank environment favors short-vega structures (credit spreads, iron condors) because mean reversion in IV gives them a tailwind on top of theta.
How Treeova uses it
Arch-AGI's volatility lens explicitly evaluates net portfolio vega before recommending entry into a new position. An agent already heavily short vega will see new short-vega ideas down-weighted in its conviction score — the platform actively manages concentration risk on the vega axis, not just the delta axis.