Korea Exchange activates a sidecar on KOSPI after KOSPI 200 futures fall by around 5%, with programme trading halted for five minutes

Sidecar activations on the Korea Exchange are mechanical rather than discretionary: a fall of a defined magnitude in KOSPI 200 futures triggers a fixed five-minute halt in programme trading orders, leaving direct order flow untouched. Episodes of this kind have tended to cluster around abrupt macro shocks, overnight gaps from US sessions, or sharp moves in the won, and the halt itself is a pacing device rather than a stabiliser: on previous occasions selling has resumed when programme orders return, though the pause does interrupt momentum-driven futures flow and narrows the cash-futures basis dislocation that programme selling tends to widen. The distinction worth drawing is between a sidecar, which suspends programme orders briefly, and a full circuit breaker, which halts the whole market at deeper thresholds and is far rarer; escalation from the former to the latter would signal a materially different degree of stress. What bears on the follow-through is the trigger: whether the move originated in offshore flows through futures, a currency leg, or idiosyncratic heavyweights, since Samsung and other large caps dominate index futures mechanics. The tells in past episodes have been the behaviour of the won and foreign futures flow in the minutes after the halt lifts.