Google Cloud is transitioning to autonomous software development lifecycle security using AI agents. These agents are embedded across all stages of development, from design to production, to continuously strengthen products. Manual processes like threat modeling are replaced by agent-based reviews that cross-reference designs against security requirements. Google Cloud developed the Mantis framework for scalable, context-aware AI code scanning, which condenses repositories to reduce overhead. Specialized agents within Mantis analyze code structure, investigate files, and filter findings to eliminate false positives. A reproduction sandbox verifies exploitability before alerting developers. Self-healing fuzz testing is employed to uncover runtime vulnerabilities without manual intervention. An autonomous patching pipeline automates the reproduction, context mapping, fix generation, and validation of vulnerabilities. Post-launch, an autonomous security posture management system continuously monitors production systems for configuration drift. Through continuous augmentation via self-reflection, successful security patterns are stored to improve future agent performance, moving towards "immune" software that self-heals.