The US stock market is nearing a third straight year of double-digit gains, driven by AI optimism, easing rate expectations and steady growth, with the S&P 500 up over 17% in 2025 after strong rallies in 2023 and 2024. However, sustaining the rally into 2026 will be tougher and hinges on robust corporate earnings, a supportive Federal Reserve and continued AI-led investment.