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:
Technology
New Module of the Week post by Maxwell Brown, featuring RcMap.
Better late than never - this week's Module of the Week is all about RcMap, @EffectTS_ 's reference counted map module. See you nerds at Office Hours tomorrow! effect.website/blog/module-of…
Effect v4 RC updates.
This week brought a major runtime performance pass, with dozens of fixes eliminating wasted work across Schema compilation, the core run loop, Queue, Stream, and Scope, alongside several new APIs and continued RC hardening.
Runtime performance pass : Stopped the Effect run loop from building a successExit between continuations, stoppedQueue /TxPriorityQueue from doing unnecessary re-sorting and traversal work, stoppedMutableList from retaining a slot for every element that ever passed through a never-emptying list, stopped forkedScope s from registering a finalizer just to leave their parent, and fixedStream.forever /Stream.repeat slowing down and leaking memory on every repetition.
Schema compilation performance : Compiled recursive Schema equivalence once instead of once per value level, stopped Schema compilation re-analyzing every sub-schema for each enclosing schema, stopped rebuilding parser wrappers on everySchemaParser.asserts call, stopped compiled Schema structs retaining an unused parse traversal, and stopped a recursive Schema formatter holding one compiled body per level.
Concurrency correctness fixes : FixedQueue takers and offers parking forever after a yield, fixed a lost wakeup during taker registration, fixed cleanup registration interruption gaps, fixed spans that never end when a traced region is interrupted as it starts, fixedLayer.MemoMap hanging or leaking a shared layer when a requester is interrupted, and madeawaitAllChildren interruptible.
New APIs : AddedConfig.flatMap , addedSchema.StringForLiteralAutocomplete , added family-awareNetAddress type helpers, addedisPubSub ,isTxChunk , andisPlatformError type guards, and added dual forms to several existing APIs.
Module reorganization : MovedArbitrary to the top-level module, moved several unstable Effect modules to top-level paths, split encoding formats into dedicated modules, and renamed the HTTP API module path.
Cluster & workflow : Fixed workflow execution ID collisions from ambiguous hash inputs, and bounded local entity registration waits.
AI providers : Added support for raw JSON Schema dynamic tool calls, fixed Anthropic gateway 4xx error mapping, retried OpenAI WebSocket turns after aprevious_response_not_found error, and preserved streamed text and tool arguments for nullable delta role and tool call IDs.
Bundle size : ReducedBigDecimal bundle size, and builtMime lookup tables lazily on first use instead of eagerly.
Documentation : Clarified JSON Schema decoding with the canonical codec, and refreshedPlatformError migration guidance.
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: August 2026 Updates.
Other technical updates from the past week.
Effect SQL
- Fix Kysely result plugins with Effect SQL clients (Bug Fix)
- Fix sql-pg pool cleanup after failed readiness probe (Bug Fix)
Community Events
Effect NYC Meetup was a blast! Thanks to all the attendees, Zach Sherman, and Hyper for hosting us! The NYC @EffectTS_ community was out in force tonight! Huge shout out to @zshrm and Hyper for hosting us in their amazing office! Had an awesome time with the rest of the Springbird team! Thanks for hosting an awesome event! The NYC @EffectTS_ community was out in force tonight! Huge shout out to @zshrm and Hyper for hosting us in their amazing office!
We have one more meetup in the US next week. Join us at Effect San Francisco on Sep 30 at CodeRabbit.
Effect Paris 🇫🇷 meetup is scheduled for Tuesday, Oct 13!
Only a few 2-day passes left for Effect Days 2026? The conference is scheduled for December 9–11 in Livorno, Italy. I’ll be speaking here about @warpdotco’s effect journey Effect Days is back 🇮🇹 Join us on December 9–11 for three days with the people building Effect and the people building with it. Workshops. Talks. Community. Early Bird tickets are now live ↓ effect.website/effect-days
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.
Effect Adoption Partner
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 ➡️ We've launched an @EffectTS_ Training Workshop Sign up for
Community Highlights
- 🤝
I sort of feel like @astrodotbuild should do something to integrate with @EffectTS_ some how. I have no actual ideas here so don't ask me, it just feels directionally the right thing to do.
I was in on @EffectTS_ two and a half years ago, receipts: x.com/matthewcp/stat…
Very excited. I remember a number of years ago there were a number of attempts to do similar things in regular JavaScript that didn't catch on. I think TypeScript has made it much more viable. I think it's one of the most important libraries being developed today.
- Can’t wait for the episode to come out!
we just recorded a @NextTokenShow episode where @RhysSullivan dives into how he’s using this exact stack! It’s so good
in Executor v2, it's actually taking advantage of effect's error system now all of the error states will have clear error messages, along with that, for the ones that are fixable via your agent i.e apps using the wrong auth they will include a prompt to use
- Anyone?
anyone else wanna join me in pressuring @benswerd to make an @EffectTS_ SDK for @freestyle_dev
- An Effect talk at React Alicante, by Violina Popova.
Amazing talk by @PopovaViolina on using @EffectTS_ to tame race conditions, errors and retries!
- Welcome, Fernando!
i started using effect this week...and i think i'm really enjoying it
Coach & Executive by MasterClass built with Effect.
saas-starter - a production-ready multi-tenant B2B SaaS template built on Effect 4, React 19, TanStack Start, Postgres with row-level security, Redis, and Stripe, shipping with auth, billing, and tenant isolation already implemented. By Vantion Labs.
Sweetener - hygienic, declarative macros for TypeScript. Try the Effect do-notation macro in the playground.
Cause & Effect Podcast
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.
Effect Team Content Update
- Effect Office Hours 47 🔥
- Effect-mq: Background jobs for Effect w/ Adam Rankin, Warp CTO.
- PersistedQueue | Module of the Week #1 by Maxwell Brown.
Effect Job Opportunities
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.
Explore Effect job opportunities →
Disclaimer: Please note that these job postings are shared for informational purposes, and we encourage applicants to verify details directly with the hiring companies.
Effect Merch Store
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
Closing Notes
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