Chinese biotech firm WuXi AppTec has been one of the market's hottest stocks this year, but its 80% rally is starting to attract a growing group of skeptics. Short positions relative to free float have risen the most among Hang Seng Index stocks over the past four weeks, according to data provider S3 Partners.

Bearish wagers climbed to 23.4% of free float as of Thursday, approaching levels last seen in August 2025, when the figure reached about 28%. The surge in short interest reflects mounting doubts about the sustainability of the stock's advance amid regulatory uncertainties and geopolitical tensions affecting the contract research sector.

Analysts note that while the company's fundamentals remain strong, the elevated short positioning could amplify volatility if positive catalysts emerge. Investors are closely monitoring upcoming earnings and any shifts in U.S.-China biotech policy for directional cues.