How we rebuilt our notification platform to fanout millions of notifications without timing out

Patreon sends billions of notifications each year. As our largest creator audiences grew, a legacy task responsible for generating millions of recipient-specific notifications began consistently timing out. This post explains how our team introduced a two-stage fanout architecture, isolated email, push and in-app processing, improved observability, and migrated more than 200 notification types across a 13-year-old codebase.