Custom Class Serialization in Workflow SDK (opens in new tab)

**Published:** April 2, 2026 | **Authors:** Nathan Rajlich, John Lindquist --- Workflow SDK now supports custom class serialization, letting you pass your own class instances between workflow and step functions. Workflow SDK serializes standard JavaScript types like primitives, objects, arrays, `Date`, `Map`, `Set`, and more. Custom class instances were previously not supported because the serialization system didn't know how to reconstruct them. With the new `@workflow/serde` package, you...