Retirement Planning 401(k) Auto-Enrollment Mandate Goes Live in 2026: SECURE 2.0 Section 101 Defaults Every New Plan at 3 to 10 PercentMay 12, 2026 SECURE 2.0 Section 101 makes auto-enrollment mandatory for new 401(k) plans in 2026. Vanguard: 87% participation vs 52% without. Amendment deadline Dec 31.