Capital One's $5.15B acquisition of Brex (announced January 22, expected to close mid-2026) is the largest bank-fintech deal in history. Brex's AI-native platform uses agents to automate expense management, corporate card issuance, and real-time payments workflows. Combined with the $35.3B Discover merger, Capital One is building the first vertically integrated bank-fintech-payments-network stack. The deal has triggered secondary M&A activity as competitors seek to match the combined capabilities.