Effect v4 beta has been released with a completely rewritten core fiber runtime that reduces memory usage and cuts bundle sizes dramatically — a minimal program drops from ~70 kB in v3 to ~20 kB in v4. The release unifies all ecosystem packages under a single version number, consolidating @effect/platform, @effect/rpc, and @effect/cluster into the main effect package. A new unstable module system (effect/unstable/*) ships 17 modules covering AI, HTTP, SQL, RPC, CLI, and more, allowing rapid feature development without semver commitments. The core programming model remains unchanged, and official v3-to-v4 migration guides are available, with codemods and AI-assisted tooling planned.
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