Wall Street experienced its strongest cross-asset performance since 2009 in 2025, with stocks and bonds rising together, credit spreads tightening, and commodities advancing as inflation eased. This broad rally, driven by AI investment, resilient growth, and accommodative policy, led to financial conditions nearing their loosest levels. However, analysts caution this alignment creates a "diversification mirage," potentially narrowing the margin for error as repeating last year's gains in 2026 appears challenging.