In 2025, Patreon tackled the challenge of delivering new features to over 10 million paying members while simultaneously upgrading its infrastructure. Their Year in Review outlines lessons learned from 12 key projects, emphasizing the importance of maintenance over new development. A report from May 2025 highlighted that 50-80% of software development costs go toward maintenance, an economic reality reflected in Patreon's approach. The engineering team's focus was on perfective maintenance and brownfield evolution, given the platform's extensive user base of 300,000 active content creators. One major project involved migrating 50TB of production data from self-managed EC2 MySQL to Amazon Aurora. Rather than risk downtime with a traditional lift and shift, the engineers implemented a defensive migration strategy that allowed them to run both systems concurrently. This redundancy was critical when latency spikes occurred due to a configuration issue in Aurora, enabling an immediate failback to the EC2 setup. Another significant challenge was removing a legacy React Router mired in technical debt. The team first built observability and feature-flagging tools, which facilitated a careful transition to a new Next.js architecture. The engineering effort also focused on breaking rigid data relationships that limited product expansion. The Multiple Podcasts project required a significant refactor of the core identity model, which had long assumed a one-to-one relationship between creators and RSS feeds. In another initiative, the introduction of subscription gifting necessitated a redesign of the billing state machine to handle multiple subscription states simultaneously. Lastly, Patreon prioritized consistency in its distributed systems, opting for atomic transactions in the Autopilot marketing engine to prevent data divergence. They moved away from high-throughput batch processing to ensure alignment between database writes and email sends, addressing the phantom retry problem. This strategic focus on architectural improvements illustrates how targeted engineering can support user growth and enhance platform stability.