Kospi surges 3% on Anthropic IPO news, triggering buy-side sidecar

South Korea's benchmark Kospi surged more than 3% Tuesday as investor sentiment revived on news that US AI company Anthropic had filed for an initial public offering.

Large-cap semiconductor stocks led the rally amid simultaneous net buying by foreign and institutional investors, with a buy-side sidecar triggered during the session. A decline in global oil prices driven by easing Middle East tensions also lent support to the rebound.

The Kospi closed at 5,638.34, up 168.87 points, or 3.09%, from the previous session, according to Korea Exchange. The index opened sharply higher at 5,658.65, a gain of 189.18 points, or 3.46%, and continued to surge through the morning, prompting a buy-side sidecar — which suspends program buy orders for five minutes — at 10:13 a.m. It was the first such trigger in four sessions since Wednesday. The Kospi has swung between gains and losses every session since Oct. 19, sustaining a streak of elevated volatility.

Foreign and institutional investors drove the advance. Foreigners ended two consecutive sessions of net selling to post net purchases of 591 billion won ($447 million). Institutions also net bought 282 billion won, while retail investors net sold 949 billion won.

The moves were widely attributed to a revival in semiconductor-focused investor sentiment following reports that Anthropic, the US developer of the AI model Claude, had submitted an IPO application.

Anthropic is reportedly targeting a valuation of up to $2 trillion and aims to raise $100 billion through the offering. If realized, it would be the largest-ever debut on US markets. The release of Anthropic's S-1 filing appeared to heighten expectations for returns on AI investment.

Hopes for a de-escalation in the Middle East also contributed to the rally, after senior officials from Saudi Arabia, Pakistan and Turkey visited Iran, pulling international oil prices lower overnight.

Samsung Electronics closed up 4.23% and SK hynix rose 5.18%. SK hynix had fallen into the 1.2 million won range after a sharp drop of 11.06% on Oct. 15, but Tuesday marked its first close back above 1.3 million won in nine sessions.

Among other top market-cap stocks, most finished higher, with Samsung Biologics (-5.37%) and Celltrion (-0.74%) the notable exceptions. SK Square surged 7.67% and Samsung Electro-Mechanics gained 7.42%, while LG Energy Solution (2.00%), Hyundai Motor (0.87%), KB Financial Group (0.27%) and Samsung Life Insurance (3.45%) also advanced.

The Kosdaq also posted strong gains. The index opened up 15.88 points, or 2.18%, at 743.09 and closed at 743.83, a rise of 16.62 points, or 2.29%, from the previous session — its first gain in four sessions since Wednesday. Retail investors were the sole net sellers at 166 billion won, while foreigners net bought 24.5 billion won and institutions net bought 150 billion won.

Among top Kosdaq stocks by market cap, all finished higher except Alteogen, which was flat, and Samchundang Pharmaceutical, which slipped 0.69%. Ecopro rose 6.74%, Ecopro BM gained 5.58%, Jusung Engineering climbed 4.30%, Rainbow Robotics added 1.15%, HLB rose 1.66%, EO Technics gained 4.22% and Leeno Industrial advanced 4.07%.

The won weakened slightly against the dollar. As of 3:30 p.m. in the Seoul foreign exchange market, the won-dollar rate stood at 1,323.7 won, up 0.6 won from the previous session.