When short volatility is the right answer for a treasury

Long convexity is not a religion. There are regimes in which a calibrated short-vol or structured-yield position is the right expression for a treasury, sized inside policy and bounded by clear exit ramps. The mistake is doing it for the wrong reason: as a yield reach in a tight spread environment, or as a default because the desk has always run that way. The right reason is regime, not habit.

Three regimes where short-vol is defensible

Compressed implied vol after a confirmed regime change. Implied that has compressed because the realized has compressed (and because the catalyst that broke the prior regime has resolved) is not the same as implied that has compressed because the cycle is mid-trend. The first justifies a defined-risk short-vol overlay, sized small, with a defined unwind trigger. The second does not.

Funding through structured product issuance. A treasury that issues a convertible or a structured note is implicitly selling volatility in a structured form. The hedge is to recognise the position, mark it, and offset it with the right instrument; not to ignore it. A program that engineers the issuance and the offsetting overlay together can extract value the issuance alone cannot.

Defined-risk yield against a buffer. A treasury sitting on a liquidity buffer has, in the buffer, a position that is short nothing and long carry. Selling carefully-sized, defined-risk vol against the buffer translates that idle balance into measurable income, with the loss bounded to the position size. The instrument matters: short puts on the underlying are not the same as a put-spread, even when the premium looks similar.

Sizing

Short-vol expressions get sized against vega, not premium. The premium is the cost of the trade; the vega is the exposure. A book sized to a target dollar-of-premium is a book that has lost discipline at the first volatility event. Sizing against vega, with the vega cap a fraction of the policy-level balance-sheet sensitivity, keeps the program inside what the board has authorised.

Guardrails

Three guardrails, written in the policy:

A vol cap. An implied-vol level above which the program cannot add new short-vol exposure. The cap is set in absolute terms, not relative; it does not move when the regime moves.

An exit ramp. Pre-defined unwind sequence, indexed to specific market triggers, that converts the short-vol book to a defensive posture without requiring a fresh board decision in the middle of the move.

A scenario rehearsal. Quarterly documented scenario run on the position as it stands; the scenario script is fixed, the inputs change, the output is filed alongside the position report.

When not to do it

If the case for short-vol depends on the assumption that the regime persists, the case is wrong. The position should be defensible if the regime breaks tomorrow, because regimes do break. A short-vol book that requires the world to keep being the way it is in order to make money is not a treasury position; it is a bet, and most boards have not authorised the company to take that bet.