This Week in Effect - 141

Hi Effecters!

Welcome back to This Week in Effect, your weekly update of the latest developments in the Effect community and ecosystem.

Effect is the TypeScript library for the AI era, helping developers build complex, synchronous, and asynchronous programs. One key feature that sets Effect apart is how it leverages structured concurrency to provide features such as async cancellation and safe resource management, making it easier to build robust, scalable, and efficient programs.

To get started, below you’ll find links to our documentation and our guide for installing Effect. Enjoy!

Recent major updates:

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New Module of the Week post by Maxwell Brown, delving into Cluster idempotency. At-least-once delivery means you never lose a message, but you'll sometimes get the same one twice. This week learn how to: → Make handlers idempotent → Skip duplicate messages → Deal with the dual write problem Module of the Week: Cluster, Part 4 ↓

A week of new modules and a big push on EventLog, alongside the ongoing stream of fixes across the codebase. Here are the most notable changes.

Additions : Added a nativeMcpClient ,effect/persistence/CircuitBreaker ,Schema.toStandardJSONSchemaV1 , aTextDiff module for minimal edit scripts and unified diffs, and Cloudflare AI Gateway support. Streaming encodings now include zip, XML andJsonArray for large JSON arrays, andBase64Url.encodePadded was added. Also added typed HTTP date andRetry-After header values toHeaders ,FileSystem.lstat ,Flag.withNegation andFlag.withoutNegation ,Command.validate for rules across CLI flags, askipInitialRun option for seeded effect atoms, and deterministic concurrent property checking for tests. #

EventLog : Entries are now encrypted in batches and get ids from a hybrid logical clock, withEventLog.writeMany and monotonic entry ids. Conflicts are ordered by entry id across journals and server, writes are acknowledged rather than echoed to the writer, and compaction can now drop entries only.SqlEventJournal gained upload checkpoints and secondary indexes, and remote replay was sped up with cached conflict payloads, indexed lookups and less per-entry overhead. Also fixed out-of-order unencrypted replication, duplicate encrypted SQL event broadcasts, and several IndexedDB journal and checkpoint issues. #

Cluster & workflow : Fixed shard release stalling on a defect restart,ClusterCron initial scheduling recovery, duplicate workflow compensations after memory-engine replays, and interrupts being lost while a workflow run saves itsSuspended reply. Stalled shard releases are now warned about repeatedly, with a new releasing-shards gauge and a shard release duration timer. Cluster storage reads also wake up when an entity registers. #

HTTP, RPC & platform : Added opt-in request batching to the HTTP RPC client protocol, streaming request payload support toHttpApi , and HTTP/2 servers inNodeHttpServer . Forwarded headers now require a trusted proxy policy. FixedHttpClient.followRedirects dying on an invalidLocation header,basicAuth credentials not being encoded as UTF-8, multipartContent-Disposition filename decoding, andNodeHttpServer ending failed streamed responses as complete. On the runtime side, fixed Bun WebSocket interruption on close, Deno response failures andSocket.readerString corrupting characters split across frames. #

SQL & AI :PgClient gained anonAcquire hook and anacquireTimeout , PostgreSQL server errors are preserved when the connection closes, andSqlClient callbacks now run after the outermost transaction commits. SQLPersistedQueue settlements are fenced by acquisition. On the AI side, added the OpenAIsafety_identifier andprompt_cache_retention request options plus prompt cache breakpoints on image and file input, and fixed composed tool failure causes being lost and retry classification for provider response decoding failures. #

Core, Schema & collections : The audit kept going with fixes forCause.pretty on cyclic cause chains,Fiber.runIn andEffect.forkIn hanging, scoped forks running after scope closure,Effect.repeat turning aDone failure into a success, andStream.retry slowing down on every retry. Defects now take precedence over typed failures in more recovery operators. Schema fixes coverSchema.Tuple encoding with omitted optional elements, Unicode casing checks,Schema.toFormatter andSchema.toTaggedUnion . Layers are now memoized by identity, and finite number and base64 validation run in linear time. #

Config, CLI & parsers : Fixed YAML block scalars with tabs,Ini.parse dropping a trailing backslash, TOML empty quoted keys,Config.schema dropping record keys for non-string key schemas,OTEL_RESOURCE_ATTRIBUTES values containing= , and several CLI lexer edge cases with clustered short options. Also fixedDateTime.formatIsoDate for extended years,zoneFromString rejectingGMT , and nanosecond precision inDuration strings and inputs.

You can follow the full changelog in the effect repository. To catch up on more updates, check out Effect v4 Updates, starting from the recently published Effect v4 RC: September 2026 Updates.

Other technical updates from the past week.

- [Render inherited CLI flags in their own help section with formatter collapse options](https://github.com/Effect-TS/effect/pull/9276) (Bug Fix, next-minor)
- [Add schema-aware streaming CSV encoding and decoding](https://github.com/Effect-TS/effect/pull/9291) (Feature, next-minor)
- [Expose migration-free encoded SQL message storage construction](https://github.com/Effect-TS/effect/pull/9330) (Feature, next-minor)
- [Set column to undefined on CSV header errors](https://github.com/Effect-TS/effect/pull/9427) (Bug Fix, next-minor)
- [Add Unhandled logging option to ignore combinators](https://github.com/Effect-TS/effect/pull/9510) (Bug Fix, next-minor)
- [Report unobserved resource release defects](https://github.com/Effect-TS/effect/pull/9388) (Bug Fix, next-minor)
- [Fix sql.insert and sql.updateValues crashing on an empty list](https://github.com/Effect-TS/effect/pull/9453) (Bug Fix, next-minor)
- [Add Glob module and portable FileSystem.glob](https://github.com/Effect-TS/effect/pull/9438) (Feature, next-minor)
- [Fix TOML inline tables and arrays being extended after definition](https://github.com/Effect-TS/effect/pull/9537) (Bug Fix, next-minor)
- [Fix TOML multiline strings that end with quotes before the delimiter](https://github.com/Effect-TS/effect/pull/9532) (Bug Fix, next-minor)
- [Detect unsupported FetchHttpClient streaming request bodies](https://github.com/Effect-TS/effect/pull/9567) (Bug Fix, next-minor)
- [Replace effect/Crypto with per-family effect/crypto modules](https://github.com/Effect-TS/effect/pull/9126) (Feature, next-minor)
- [Fix(http): send stored cookies only to the matching host](https://github.com/Effect-TS/effect/pull/9614) (Bug Fix, next-minor)
- [Add terminal resize stream](https://github.com/Effect-TS/effect/pull/9639) (Bug Fix, next-minor)
- [Allow database clock lag in PersistedQueue SQL delay tests](https://github.com/Effect-TS/effect/pull/9642) (Bug Fix, next-minor)
- [Add encrypted remote compaction to the event log](https://github.com/Effect-TS/effect/pull/9571) (Improvement, next-minor)
- [Add McpTest in-memory client for McpServer registrations](https://github.com/Effect-TS/effect/pull/9657) (Feature, next-minor)
- [Add opt-in RFC 9457 Problem Details to HttpApi](https://github.com/Effect-TS/effect/pull/9706) (Feature, next-minor)
- [Add RpcServer onDisconnect option](https://github.com/Effect-TS/effect/pull/9688) (Bug Fix, next-minor)
- [Fix Toml.parse accepting out of range dates and times](https://github.com/Effect-TS/effect/pull/9648) (Bug Fix, next-minor)
- [Add request-aware visibility to McpServer](https://github.com/Effect-TS/effect/pull/9661) (Improvement, next-minor)

- [Restore Anthropic spec fetching and schema regeneration](https://github.com/Effect-TS/effect/pull/9509) (Bug Fix, next-minor)
- [Raise pnpm fetch timeout for large CI tarball downloads](https://github.com/Effect-TS/effect/pull/9627) (Bug Fix, next-minor)

• Wait for failure-suspended workflow activity replay in test (Bug Fix, next-minor)

• Parameterize OpenAPI client with error/requirements generics (Feature, next-minor)

• Fix(opentelemetry): keep optional trace sdk peers out of the root entrypoint (Bug Fix, next-minor)

- [Bound synchronous Node readable and socket drains](https://github.com/Effect-TS/effect/pull/9327) (Bug Fix, next-minor)
- [Add Glob module and portable FileSystem.glob](https://github.com/Effect-TS/effect/pull/9438) (Feature, next-minor)
- [Replace effect/Crypto with per-family effect/crypto modules](https://github.com/Effect-TS/effect/pull/9126) (Feature, next-minor)
- [Add terminal resize stream](https://github.com/Effect-TS/effect/pull/9639) (Bug Fix, next-minor)
- [Default Bun idle timeouts to off and document streaming timeouts](https://github.com/Effect-TS/effect/pull/9705) (Bug Fix, next-minor)

• Fix(sql-mssql): keep interrupted requests leased until Tedious settles them (Bug Fix, next-minor)

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If you’re thinking of joining Effect Days 2026 this December in Italy, you’d better hurry.Huge thanks to all our sponsors for helping us bring the Effect community together in Italy this December. 🤍 We're so happy to have you on board! @zivergetech@EffectfulTech@warpdotco@executorsh@academind_real@Cloudflare@novelcraftereffect.website/effect-days#sp… #

All three Effect Miami speakers have been announced! The meetup is scheduled for Nov 9. 🚀 Excited to announce John De Goes @jdegoes as our main speaker for Effect Miami #3! It’s a real honor to welcome John, one of the most influential voices in modern functional programming. Creator of ZIO, founder of Ziverge, and Golem Cloud, his work has helped shape how we🚀 Excited to welcome 𝗛𝗮𝗿𝗿𝘆 𝗦𝗼𝗹𝗼𝘃𝗮𝘆 ( @harrysolovay ) to 𝗘𝗳𝗳𝗲𝗰𝘁 𝗠𝗶𝗮𝗺𝗶 #𝟯! I first discovered Harry through his incredible hardcore TypeScript tutorials on YouTube. His depth of knowledge, creativity, and ability to push the boundaries of the type system🚀 Excited to welcome 𝗗𝗲𝘃𝗶𝗻 𝗝𝗮𝗺𝗲𝘀𝗼𝗻 ( @devinjameson ) to 𝗘𝗳𝗳𝗲𝗰𝘁 𝗠𝗶𝗮𝗺𝗶 #𝟯! Devin is the creator of@foldkit , an ambitious open-source frontend framework built on Effect and inspired by The Elm Architecture. Foldkit rethinks frontend development around #

Effect Warsaw #2 is coming up on November 17!Effect Warsaw #2 is coming next month! 👉 Sam is going to talk about full stack effect. More talks, 🍕 and 🍻 coming too! luma.com/k5o7m2pg #

Effect Office Hours 🔥 every Wednesday at 10:00 AM ET / 16:00 CET on our YouTube channel . Visit our Effect Community Events calendar and subscribe for updates on upcoming Effect events.

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Max at Cloudflare Connect at cloudflare connect! effect cluster on DOs! #

If we had a penny… i was wrong about effect when @schickling bent my ear for an hour at next conf (rip) 2 years ago i told him it would never happen impossible nobody has time for all that because@EffectTS_ is a lifestyle choice, developers resist change, it's too much surface area and #

💯 Opus 5.5 with @EffectTS_ is the best combination ever #

effect-api-query - generate typed TanStack Query options and cache keys from Effect RPC and HTTP API contracts. By ueberBrot. #

kabuki - run your app as a tree of state-machine Actors outside React, built on Effect Schema, scoped Effects, and Layers. By pkishorez. #

effect-snowflake - an Effect v4 Snowflake client built on Apache Arrow ADBC, returning results as Arrow tables and record batches. By RyanCallahan312. #

effect-mongodb - Effect-based APIs for working with MongoDB. Version 0.8.0 is out and supports Effect v4. By doubleloop-io.

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We’re thrilled to announce Ziverge as the first Effect Adoption Partner!

Here are 3 things we're thrilled to announce, as part of our partnership with @EffectfulTech, creators of @EffectTS_ 🔥 ➡️ Ziverge will be sponsoring Effect Days

➡️ We have produced an Effect SDK for [@GolemCloud](https://twitter.com/GolemCloud)
➡️ We've launched an [@EffectTS_](https://twitter.com/EffectTS_) Training Workshop

Sign up for

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Looking for a role where you can work with Effect? We now have a dedicated Effect jobs page featuring open roles from companies that use Effect. We’ll keep it updated as new opportunities come in.

New this week: **Bitfocus** & **Warp** are hiring Effect engineers.

[Explore Effect job opportunities →](https://www.effect.website/effect-jobs)

Disclaimer: Please note that these job postings are shared for informational purposes, and we encourage applicants to verify details directly with the hiring companies.

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Don’t forget to listen to our Cause & Effect podcast hosted by Johannes Schickling and available on YouTube, X(Twitter), and audio platforms like Spotify and Apple Podcast.

John A. De Goes, the creator of ZIO, as well as CEO of Ziverge and Golem Cloud, joins Johannes Schickling and Michael Arnaldi to discuss how AI is reshaping software engineering, what developers should still learn, and why Effect’s primitives are especially valuable for coding agents.

Play

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• Effect Office Hours 51 🔥

Play

• Native Arbitraries, Schema Binary, and PostgreSQL | Office Hours 43

Play

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The Effect Merch Store offers a selection of Effect-branded items designed for the community. All orders are processed and fully managed through Printful.

Effect Merch is here! We’re excited to announce the launch of our Effect merch page! Grab your favorite swag & show your love for Effect in style! 🧢

effect.website/merch

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That’s all for this week. Thank you for being a vital part of our community. Your feedback is highly valued as we fine-tune this format. Feel free to share your thoughts, and we’ll do our best to tailor it to the needs of our community.

Effect Community Team

Previous Module of the Week - Cluster, Part 4

source & further reading

effect.website — original article This Week in Effect - 140 This Week in Effect - 139 Effect 4.0: The First Week