The U.S. stock market saw some dramatic moves past week with five stocks posting the largest weekly gains and drops (Mon-Fri Sept 22-26, 2025). For each, we highlight the drivers of the move and year-to-date (YTD) performance.

To track momentum in real time, you can use FMP's Top Traded Stocks API to see the most actively traded names. With your FMP API key, the Investor Dashboard provides a comprehensive view with deeper context - insider trades, stock price targets, revenue segmentation, and EPS trends.

Top 5 Gainers/Losers

Lithium Americas (LAC)

Shares nearly doubled (+~90%) on Wednesday after reports that the Trump administration is considering a 10% ownership stake in the miner's Thacker Pass lithium project. This high-profile government backing (to secure critical battery minerals) ignited a rally. YTD: roughly +110% as earlier gains in lithium stocks carried into the fall. Watch: Federal support for critical minerals and Thacker Pass permitting.

Crinetics Pharmaceuticals (CRNX)

The biotech climbed strongly (~+25%) this week as FDA approved its new oral acromegaly drug “Paltusotine,” the first daily pill for that rare disorder. Analysts immediately raised price targets, reflecting optimism about peak sales (~$1.5B for the treatment) and pipeline prospects. YTD: ~+11%. Watch: uptake of Paltusotine and upcoming development milestones.

Mirion Technologies (MIR)

Shares rallied about +35% after the radiation-detection firm announced it had upsized a convertible debt offering to $325 million. Proceeds will fund its planned $585 million acquisition of Paragon Energy Solutions (via WCI-Gigawatt) and related costs. Investors cheered the deal financing and Paragon's potential to expand Mirion's industrial energy business. YTD: roughly +10%. Watch: Paragon integration and technology lift post-close.

CarMax (KMX)

The used-car retailer's stock fell ~20% on Sep 25 after its Q2 (Aug) earnings badly missed expectations. Revenue of $6.6 B (down 6% YoY) and EPS of $0.64 trailed consensus (EPS ~$1.05), as weak demand forced CarMax to cut prices. Management cited declining customer traffic and inventory pressures. YTD: about -44% (shares near multi-year lows after a tough year). Watch: used-car market dynamics and Q3 guidance.

Uber Technologies (UBER)

Uber slid about -5% mid-week after Google's Waymo announced it will offer fully driverless rides via Lyft next year. This unexpected competition move hit Uber's self-driving ambitions and Lyft's stock popped 13% on the news. (Uber is up about +40% YTD despite this dip.) Watch: rideshare market share, Waymo's expansion, and Uber's autonomous/driver costs.

Track Market Liquidity in Real Time with FMP's Top Traded Stocks API

The Top Traded Stocks API shows which tickers are commanding the most attention right now—a handy complement to weekly performance:

• Most Active Lists: Instantly see the highest-volume stocks across major U.S. exchanges (or filter by NASDAQ/NYSE).
• Real-Time Volume + Price Metrics: Monitor volume, price change, and % change to gauge momentum and liquidity.
• Company Snapshot: Pull names, symbols, and trading volume for quick context.

Example use case: A day trader scans NASDAQ via the Top Traded Stocks API and spots iSun (ISUN) printing unusually high volume. With real-time volume and price-change data in hand, they can decide whether the momentum fits their setup before entering a trade.