Nebius (NBIS) shares tumbled 5.08% in pre-market trading, as investors rushed to lock in profits following a stunning rally in the previous session.

The pullback comes after the AI cloud infrastructure company's stock skyrocketed 34% on Wednesday, fueled by second-quarter earnings that crushed expectations. The pre-market reversal is largely attributed to profit-taking after the parabolic move. Adding to the downward pressure, bearish signals emerged in the options market, where a significant sell order on far out-of-the-money call options indicated that institutional investors are skeptical about further upside in the near term.

Furthermore, post-earnings scrutiny has intensified around the company's capital expenditure. Though Nebius reported a 454% revenue surge, its quarterly capex came in at a massive $5.6 billion, with customer prepayments covering only 50% to 60% of associated costs. This mismatch has raised concerns about the sustainability of its financial model, prompting some investors to reduce their positions after the stock's rapid ascent.