What the closing auction changed about the last 15 minutes
Computed from Vyloka's own research archive. Educational statistics, not live data.
Since the closing auction session went live in August 2026, a stream of confused screenshots has followed: an index closing at a price it never traded during the day, option premiums swinging violently after 3:15, positions marked far from the last visible trade.
The untraded print is by design
The auction close is not the last traded price. It is the equilibrium price of the auction book — the level that matches the maximum quantity of closing orders. A print at a level that never traded intraday is how a call auction is supposed to work. Whether that design serves intraday traders is a fair debate; that it is functioning as designed is not.
What we measure
We have tracked every close since the CAS went live. Two things stand out so far: the last-15-minute move is running at a multiple of its pre-CAS average, and the next-day follow-through of that closing move is visibly weaker than it used to be. The close is carrying more motion and less meaning.
Why it matters
Two practical consequences. Carrying short-gamma exposure into the final minutes is a different risk than it was before August. And anchoring tomorrow's bias to today's closing print — a habit built over years — now rests on a price that follows through less often. The close is a different instrument now. It deserves to be treated as one.
Update — September 2026: the suspension debate
The CAS is now front-page news: a former MP has publicly asked SEBI to suspend it. Whatever SEBI decides is policy; our job is measurement, so here is the running tape as of early September, across every session since the CAS went live.
The last 15 minutes have roughly doubled. Median move from 15:15 to the close: 15.8 points across the 143 sessions before the CAS, 32.7 points across the 23 sessions since — about 2.1×. (Our first fortnight's sample showed an even bigger jump; with more data the honest figure is “doubled”, and this paragraph will keep updating as the sample grows.)
The auction itself is usually quiet. On most sessions the auction prints within a few points of the last traded price — on 2 September it printed at exactly the last trade, a 0.0-point dislocation. The days that generate angry screenshots are the exceptions, and they cluster around expiries and large closing-order imbalances.
Neither number says the CAS is good or bad — they say what it does: a livelier final quarter-hour, a usually-orderly print, and occasional dislocations worth understanding rather than fearing. If the debate reaches SEBI's table, it should be argued from tapes like this one, not screenshots.
See what kind of day today actually was
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This article describes market mechanics for educational purposes. Nothing here is investment advice, a recommendation, or a forecast — conditions, never calls.