Capital One engineers share their three-generation journey from static infrastructure-as-code to event-driven choreography to durable execution using self-hosted Temporal open source. The talk covers their AWS Fargate-based deployment architecture with RDS PostgreSQL, JWT/OIDC authorization via custom authorizer and claim mapper, OpenTelemetry observability with sidecars, and S3 archival. Key challenges included compliance-driven tech choices, custom SDK wrappers for multi-tenant onboarding, CLI token refresh, and database migration process alignment. Outcomes include 50+ infrastructure capabilities, 100+ contributors, and delivery times reduced from weeks/months to days/hours. Best practices cover workflow determinism, activity vs workflow separation, timeout standardization, versioning for long-running workflows, and developer training on durable execution patterns.