Why Did SanDisk Stock Jump?

SanDisk (SNDK) stock jumped 11.0% on Friday, September 18, 2026, its last trading day before joining the S&P 100. By the September 30 close of $1,739.89, the shares were about 3% below their September 18 close. SanDisk's last quarterly report came in early August, so the jump did not follow new results. So what drove it, and what does the price assume now.