Stock Market Today: Indexes Decline to Open October, Q4 Trading; 10-Year Treasury Yield Hits Fresh 24-Year High

Major U.S. stock indexes slipped Thursday as fourth-quarter and October trading opened, with the 10-year Treasury yield printing a fresh 24-year high and oil prices rising. Rates and energy moved against equities on the first session of the new quarter.

The yield milestone sets the tone. A 10-year at its highest level in 24 years raises the discount rate applied to equity cash flows, and rising oil adds a second pressure point on the inflation outlook. That pairing is a classic headwind for index-level risk appetite. This is interpretation of the moves, not a stated cause in the report.

One stock bucked the tape. Synopsys ranked among the best performers in both the S&P 500 and the Nasdaq after announcing AI deals with OpenAI and Amazon. The stock rallied as of the 12:24 PM EDT update on October 1, 2026, showing that named, catalyst-driven AI partnerships can attract buyers even while broader indexes decline.

The divergence is worth noting: indexes lower, yields at multi-decade highs, oil up, yet a chip-design name surging on two marquee AI relationships. Interpreting the action, money appears to be rotating toward specific catalysts rather than buying the broad market.