Effect v4 (Beta) - Development & Migration

Overview

Comprehensive guidance for Effect v4 development and migration from v3. This skill provides:

1. v4 Core Patterns - Guide to building new v4 code with Context, layers, generators, schema codecs
2. v3 → v4 Migration - Step-by-step migration guidance with API renames, behavior changes, and before/after examples

Status: Effect v4 is beta software under active development in effect-smol. The core programming model is stable, but effect/unstable/* modules may receive breaking changes in minor releases. For production use, review official v4 beta guidance and stability notes.

All bundled migration guides are sourced from the official effect-smol migration documentation.

Upstream Changes Through June 30, 2026

The upstream beta changed substantially after the original February 22, 2026 baseline and again after the April 9, 2026 skill refresh. Treat older examples that mention ServiceMap, Schema.makeUnsafe, SchemaParser.makeUnsafe, or Effect.Yieldable as stale. Current guidance should prefer: