Why Is TMC Stock Up 30% Today? Fiber-Optic Rally, No Filing (Oct 2, 2026)
TMC and Mercury are each up about 30% as of 1:30 p.m. in Seoul, near the daily limit. The only stated reason is press talk of AI data center demand; neither company has filed anything. Brils, in its second day of trading, is up 22%.
Seoul — As of 1:30 p.m. on Oct. 2, fiber-optic stocks TMC (217590) is up 29.95% and Mercury (100590) is up 29.80%. Both are attributed in news reports to expected AI data center investment, and neither company has filed a disclosure. Brils (468670), in its second day after listing, is up 22.5% with no stated reason. KOSPI is up 0.18% at 6,983.89, while KOSDAQ (Korea's tech- and small-cap-heavy market) is down 0.46% at 890.16. This article will be updated with closing figures after the market closes.
At a glance
| Stock | Why it rose | Nature | Basis | What to check next |
|---|---|---|---|---|
| TMC | Expanded U.S. big-tech investment, AI data center fiber demand | Expectation | Reports only | Company filing or orders, trading value |
| Mercury | Same fiber-optic theme, overnight surge in U.S. fiber stocks | Expectation | Reports only | Earnings or contract filings, foreign buying |
| Brils | No clear reason (day two of trading) | No reason | None | Institutional selling, trading value |
TMC (217590): fiber-optic hopes push it near the daily limit, with no filing
TMC is rising as expectations for fiber-optic demand from AI data center spending spread. Business Post and Chosun Biz reported that fiber-optic stocks were broadly strong on news of expanded U.S. big-tech infrastructure investment. But TMC has filed nothing on DART (Korea's official disclosure system) in the past seven days, so no company-specific contract or earnings announcement backs the move.
The stock is at 18,440 won, up 35.9% over two days and 28.9% over five, on 98.8 billion won of trading value and a 444.3 billion won market cap. Foreign investors net bought 83,416 shares yesterday. A rally built on expectations depends on the same theme to hold. Watch whether the company confirms fiber-optic orders or earnings in a filing, and whether trading value holds tomorrow.
Mercury (100590): up to the 30% daily limit as U.S. fiber stocks surge
Mercury hit the limit-up price of 6,250 won, which News1 and Maeil Shinmun attribute to an overnight surge in U.S. fiber-optic stocks spreading to Korean peers. Money Today also cited a space theme tied to Korea joining a NASA space telescope project and hopes for next year's U.S. spectrum auction. Mercury itself has filed nothing.
It is up 31.9% over two days and 25.1% over five, with 23.6 billion won of trading value and a 107.1 billion won market cap. It also rose 30% on Sept. 9 and then stayed in the 4,700–5,000 won range for about a month. Foreign investors net bought 50,996 shares yesterday. Whether that buying continues, and whether the company discloses concrete earnings or contracts, are the things to watch.
Brils (468670): no known reason for the rise
Brils is up 22.5% at 37,300 won on its second trading day, after rising nearly 59% on its debut on Oct. 1. The only filing is a designation as a caution stock for heavy single-account trading, and no report explains today's move. Debut-day coverage mentioned a planned humanoid center in Songdo in the first half of next year.
Trading value is 324.3 billion won and market cap is 423.9 billion won. On the first day, institutions net sold 1,327,874 shares while individuals net bought 1,756,768, meaning retail investors absorbed what institutions sold. Watch whether trading value holds tomorrow and whether institutional selling continues.