Effect v4 Beta: July 2026 Updates

Welcome to another month of Effect v4 beta. The biggest structural change of the month, and arguably of the entire beta, happened in the final week, when Effect v4 moved to the canonical Effect-TS/effect repository.

The main branch is now v4, while v3 lives on the v3 branch. The effect-smol repo is archived and read-only, with all history preserved for reference. For anyone following the beta via the effect-smol repository, the new home for development is Effect-TS/effect.

What landed in July

Native Deno Support

Added a full Deno platform integration in @effect/platform-deno, including an HTTP platform, HTTP server, socket support, socket server, cluster HTTP and socket support, multipart support, and a Deno services aggregate module.

Effect now has first-class support for Deno alongside Node.js, Bun, and the browser.

Graph Module

A new Graph module landed with a broad initial feature set: graph set operators (union, intersection, difference), opaque Graph interfaces for better encapsulation, toGraphViz DOT output, floydWarshall shortest paths, isAcyclic and isGraph predicates, a Walker iterator, and fixes for edge transforms, mutation finalization, and parallel undirected edge handling. Graph set operation gotchas are also documented.

Cron

A thorough hardening pass landed for the Cron module:

• validated Cron.make field restrictions
• fixed Cron.prev month day rollover and weekday wrapping
• fixed alias normalization, added day and weekday intersection semantics in the inspection representation, and
• corrected JSDoc examples and documentation accuracy.

Schedule

The Schedule API received its most significant overhaul of the beta. Limiting APIs were consolidated into a cleaner surface. Schedule.min and Schedule.max were added for composing schedules by output. The internal representation was simplified, and several redundant APIs were removed.

Cron semantics also improved: Schedule.cron now more closely adheres to vixie semantics, including support for step fields like 5/15 expanding from the starting value through the field maximum. A bug where Schedule.cron misbehaved when the test clock was adjusted to infinity was also fixed.

Schema

Schema work continued steadily across the month.

New types - added Schema.Decoder and Schema.Encoder types for passing simpler schema shapes to APIs that only decode or only encode. Added Schema.DateFromMillis for millisecond-epoch date decoding. Added discriminants to Schema.toTaggedUnion for more precise tagged union encoding.

Correctness fixes - fixed excess property handling in schema-backed class constructors. Fixed StructuralProto equality. Preserved content schema identifiers when emitting JSON Schema for Schema.fromJsonString. Fixed JSON Schema tuple allOf intersections. Fixed tuple post-rest element indexing. Fixed union candidate dispatch ordering. Prevented prototype pollution in bracket-path decoding. Preserved nested class construction when applying constructor defaults.

DX - simplified the displayed Type, Encoded, and Iso types of required readonly Schema.Struct fields for cleaner hover types in editors. Improved the passthrough strict: false mode example in docs.

HttpApi Hardening

The HttpApi layer received a significant hardening pass in the final week of July.

Highlights include:

• reused response schemas
• normalized payload media types
• hardened HTML rendering in API docs
• fixed client error and authorization decoding
• improved type-level performance
• kept HttpApi composition immutable
• applied transformClient when building individual endpoint clients
• rejected duplicate and unknown handler registrations with descriptive errors
• rejected duplicate OpenAPI operations and incompatible security scheme names
• compiled SSE client decoders once instead of per-request, preserved __proto__ identifiers, and
• added HttpApiError for status 422.

Earlier in the month: ensured handler errors don’t cause HttpApi security middleware to fall back to unauthenticated behavior, and fixed HttpApi to return 400 for malformed JSON request bodies.

Additional HTTP fixes:

• fixed HttpRouter middleware context inference
• routed multipart errors to HTTP responses
• fixed published pre-response handler types
• handled aborted HEAD responses during NodeHttpServer disposal, and
• fixed the OpenAPI generator’s handling of recursive schema forward references.

Security hardening

A broad security hardening sweep landed in the final week:

• stripped credentials on cross-origin HTTP redirects
• hardened cookie attribute validation
• secured MSSQL transport defaults
• hardened file-backed key-value store keys
• hardened JSON-RPC message classification, and
• escaped control characters in CLI error messages.

Migration Tooling

Added API diff tooling for v3-to-v4 migration, making it easier to identify breaking changes when upgrading from Effect v3.

Fiber Runtime

A thorough round of fiber runtime hardening landed:

• fixed pending interrupt delivery across interruptibleMask
• prevented concurrent traversal daemon leaks
• fixed FiberHandle.clear race
• cleaned up Fiber.joinAll observers on interruption
• preserved stack annotations for terminal root failures
• stored interruptor stack frames separately
• avoided runSyncExit dispatcher allocation
• made awaitAllChildren child selection linear
• fixed handling of large millisecond values passed to sleep
• fixed fiber self-interruption from inside a running observer
• fixed cache lookup to only interrupt when all awaiters are gone.

Durable Execution & Workflow

• Fixed durable race result replay.
• Ensured PersistedQueue decoding failures count as processing attempts.
• Fixed Redis-backed PersistedQueue script handling.
• Fixed SQL-backed persisted queues to refresh locks for actively acquired elements.
• Fixed a missing requiresHandler flag on a durable activity type.
• Fixed the activity retry policy.

SQL

• Added SQL.valuesUnprepared for raw value interpolation.
• Fixed sqlite-do Durable Object transactions.
• Fixed sqlite-bun to fail with a typed SqlError when statement preparation throws.
• Scoped unknown request tag failures to the request instead of the connection.
• Fixed SQL-backed persisted queues.
• Added disablePreparedStatements option to @effect/sql-mysql2.
• Avoided creating a table when it’s not needed.

Native SQLite in Node

Replaced better-sqlite3 with Node’s built-in node:sqlite module in sql-sqlite-node, removing a native dependency and improving portability across Node environments.

RPC & HTTP

• Failed RpcClient HTTP requests with a defect when the response closes early.
• Fixed the bundle resolver for package export subpaths.
• Matched NodeHttpServer.layerConfig services.
• Changed RPC IDs to string | number for broader compatibility with existing systems.
• Fixed HttpApi runtime shape.
• Allowed additional HttpApiClient options.
• Also fixed Schedule.andThenResult to correctly emit self outputs as Failure and other outputs as Success.

Atoms & Reactivity

• Added custom equality detection for atoms to prevent unnecessary re-renders.
• Fixed atom dependencies during batch rebuilds.
• Used Sets to track atom relationships for improved correctness and performance of the reactivity graph.

OpenTelemetry

• Preferred explicit OTLP resource configuration over implicit detection.
• Rendered nested error causes in tracer exception events for deeper observability into chained failures.

AI

• Fixed OpenAI compat parallel tool calls.
• Fixed encoding of system messages as input text.
• Added platform literal to HttpPlatform.
• Fixed provider-defined tools (tool cloning and Anthropic client tools).
• Removed the legacy LSP in favor of effect/tsgo.
• Fixed OpenRouter dynamic tools sending an empty parameters schema.
• Preserved OpenAI Responses cache write token usage.

LayerRef

Added a new LayerRef module for holding a reference to a Layer that can be swapped at runtime, useful for testing and dynamic configuration scenarios.

FileSystem

• Added glob support to the FileSystem module for pattern-based file discovery.
• Fixed FileSystem.watch recursive control.

CLI

• Reintroduced CLI wizard mode.
• Added CLI config for built-in flags.
• Fixed missing flag value handling. Fixed Command.withSubcommands losing context type inference.
• Fixed end-of-options operands for subcommands.
• Fixed positional argument overflow.
• Escaped control characters in error output.
• Removed the doubled “Expected” prefix from InvalidValue messages.
• Preserved chained vitest helpers like it.describe.each through the it proxy.
• Added general cleanups.

New Core APIs

Added Effect.reduce for folding over a collection of effects into a single accumulated result.

MutableList

Fixed MutableList.filter empty-state handling to prevent incorrect state after filtering all elements.

Config & URL

• Treated empty config strings as missing data, aligning with the principle of least surprise for environment variable–backed config.
• Moved UrlParams.makeUrl to Url.make for a cleaner API surface, and accepted UrlParams.Input in additional UrlParams APIs for more ergonomic URL construction.

String Utilities

Fixed string case conversion for numeric word segments, e.g. "v4Beta" now correctly converts to "v-4-beta" instead of losing the digit boundary.

Entity & Cluster

• Cached clients by entity reference for better performance.
• Isolated cluster entity handler context from the fiber that first wakes it, fixing a subtle context leak.

Performance

• Optimized Bun stream reading.
• Forked memo maps on nested layer builds to prevent cross-build contamination.
• Stopped using performance.timeOrigin and switched to lazy origin calculation to avoid issues in environments where the Performance API is restricted.
• Avoided runSyncExit dispatcher allocation in the fiber runtime.

Bun

Constructed empty Bun multipart streams per-request to prevent cross-request state contamination.

Documentation

• Fixed error names in JSDoc comments.
• Documented ChildProcess environment behavior.
• Migrated docgen.
• Clarified GenericTag key documentation.

Keep up with the Effect v4 beta

If you missed the earlier updates, the June recap and the February–May recap cover all the major changes since the v4 beta launch.

For week-by-week updates, follow the This Week in Effect series.

To try the Effect v4 beta:

npm install effect@beta

pnpm add effect@beta

yarn add effect@beta

bun add effect@beta

Happy Effecting. 🚀