[What landed in July](#what-landed-in-july) -
[Native Deno Support](#native-deno-support) -
[Graph Module](#graph-module) -
[Cron](#cron) -
[Schedule](#schedule) -
[Schema](#schema) -
[HttpApi Hardening](#httpapi-hardening) -
[Security hardening](#security-hardening) -
[Migration Tooling](#migration-tooling) -
[Fiber Runtime](#fiber-runtime) -
[Durable Execution & Workflow](#durable-execution--workflow) -
[SQL](#sql) -
[Native SQLite in Node](#native-sqlite-in-node) -
[RPC & HTTP](#rpc--http) -
[Atoms & Reactivity](#atoms--reactivity) -
[OpenTelemetry](#opentelemetry) -
[AI](#ai) -
[LayerRef](#layerref) -
[FileSystem](#filesystem) -
[CLI](#cli) -
[New Core APIs](#new-core-apis) -
[MutableList](#mutablelist) -
[Config & URL](#config--url) -
[String Utilities](#string-utilities) -
[Entity & Cluster](#entity--cluster) -
[Performance](#performance) -
[Bun](#bun) -
[Documentation](#documentation) -
[Keep up with the Effect v4 beta](#keep-up-with-the-effect-v4-beta)
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 typedSqlError
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 asFailure
and other outputs asSuccess
.
Atoms & Reactivity
- Added custom equality detection for atoms to prevent unnecessary re-renders.
- Fixed atom dependencies during batch rebuilds.
- Used
Set
s 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 toHttpPlatform
. - 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 theFileSystem
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 theit
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
toUrl.make
for a cleaner API surface, and acceptedUrlParams.Input
in additionalUrlParams
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](https://effect.website/blog/effect-v4beta-june-recap/) and the [February–May recap](https://effect.website/blog/effect-v4beta-launch-to-may-recap/) cover all the major changes since the v4 beta launch.
For week-by-week updates, follow the [This Week in Effect](https://www.effect.website/blog?category=this-week-in-effect#blog-grid) series.
To try the Effect v4 beta:
Happy Effecting. 🚀