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

The KRX sidecar is a standing circuit-breaker mechanism that suspends programme (arbitrage and basket) trading for a fixed five-minute window when KOSPI 200 futures breach the threshold, a far milder instrument than the market-wide circuit breaker that halts all trading and is triggered only at substantially larger index moves. Episodes of this kind have historically been triggered less by the level of the move itself than by the speed of it, since the threshold is percentage-based against the prior reference and tends to trip during sharp, concentrated selling rather than across a session-long slide. The mechanism's practical function is to interrupt the feedback loop between futures selling and programme-driven cash execution; the tell in past episodes has been whether selling pressure resumes immediately after the five-minute window, which would signal genuine directional flow rather than a liquidity air pocket. The distinction worth drawing is between an idiosyncratic Korea event, where follow-through tends to be contained to local indices, the won and Korea-linked futures, and a regional risk move, where the Nikkei, Taiwan and Australian contracts will already be signalling breadth. Attention falls next on whether the exchange escalates to a broader halt, on the cash open dynamics once programme trading resumes, and on any accompanying move in the won, which has historically been the cleaner gauge of whether the selling is domestic or foreign-driven.