Today's biggest winners and losers in the stock market.

On this episode of Stock Movers:Listen for comprehensive cross-platform coverage of the US market close as heard on Bloomberg Television, Bloomberg Radio, and YouTube with Romaine Bostick, Katie Greifeld, Carol Massar and Emily Graffeo.

- IBM (IBM) shares plunged on Monday, after the artificial intelligence startup Anthropic said its Claude Code tool can help with modernizing COBOL, a dated programming language that’s mainly run on IBM computers. Shares sank 13% in their biggest one-day percentage loss since October 2000. With the decline, the stock is now down 27% in February, on track for its biggest one-month percentage decline since at least 1968, according to data compiled by Bloomberg.

-Arcellx (ACLX) shares surge as much as 78% — a record — to an all-time high after Gilead Sciences agreed to acquire the biotech company for $115 per share in cash and one contingent value right of $5 per share. Stifel views the deal as a “a near-term better-case scenario” for Arcellx.

DoorDash (DASH) stock slid Monday as investors reacted to a viral post from a research group describing the food-delivery company as a "poster child" for risks from AI agents. A company cofounder responded on X after the report sparked debate on the social media platform over the weekend.