Wednesday's biggest movers: Seagate Technology sinks 9.2% and Ciena jumps 13.8%

Among US-listed companies worth at least $20 billion, the biggest moves in Wednesday's session (7 October) came from Seagate Technology, which fell 9.2%, and Ciena, which rose 13.8%.

The decliners

Seagate Technology (STX) fell 9.2% to $805.63. It was its biggest one-day drop since 2 October, based on the past year of closes. The shares are up 193% this year and 26.2% below their 52-week closing high. Coverage since the move includes Investor's Business Daily's headline “Stock Market Today: Dow Cuts Sharp Losses As Some Techs Rally; AbbVie Breaks Out (Live Coverage)”.

Guardant Health (GH) fell 8.8% to $170.69. It was its biggest one-day drop since 6 October, based on the past year of closes. The shares are up 64.8% this year and 10.1% below their 52-week closing high.

Moderna (MRNA) fell 7.8% to $187.46. It was its biggest one-day drop since 20 August, based on the past year of closes. The shares are up 566% this year and 3.4% below their 52-week closing high. Coverage since the move includes Pharmaceutical Technology's headline “CPHI 2026: Moderna builds on its COVID-era manufacturing lessons”.

Western Digital (WDC) fell 6.9% to $411.04. It was its biggest one-day drop since 2 October, based on the past year of closes. The shares are up 135% this year and 45.7% below their 52-week closing high.

The gainers

Ciena (CIEN) rose 13.8% to $443.65. It was its biggest one-day gain in the past year, based on the past year of closes. The shares are up 90.9% this year and 28.8% below their 52-week closing high. Coverage since the move includes Zacks's headline “Ciena Surges 178% in a Year: Should Investors Buy the Stock Now?”.

Constellation Energy (CEG) rose 12.2% to $300.40. It was its biggest one-day gain in the past year, based on the past year of closes. The shares are down 15.2% this year and 25.8% below their 52-week closing high. Coverage since the move includes Trefis's headline “Is Constellation Energy Stock a Good Fit For Your Portfolio Risk?”.

Vistra (VST) rose 10.8% to $160.50. It was its biggest one-day gain in the past year, based on the past year of closes. The shares are up 3.3% this year and 20.9% below their 52-week closing high.

Pershing Square (PS) rose 8.9% to $59.75. It was its biggest one-day gain since 18 September, based on the past year of closes.

The megacaps

Of the 12 most-watched names we track, 8 closed higher. Micron (MU) did best at +4.06%, and Meta (META) worst at -2.38%.