This Week in Effect - 139

Effect 4.0.1 and 4.0.2 shipped on October 5 and October 8, 2025, respectively, as the TypeScript library's first patch releases since Effect 4.0, according to Sebastian's post on the project's first week. Roughly 30 contributors landed about 150 commits on `main` in that week, with 4.0.2 adding missing `@stability` tags to modules intended to ship as unstable and the pipeline now enforcing stability levels on every module and importable export. The releases also aligned HTTP, SQL and AI spans with OpenTelemetry semantic conventions, added a `DatagramSocket` (UDP) module and PowerShell `--completions` support, and fixed Anthropic streamed tool JSON errors while caching per-tool response schemas for better AI performance.

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: New Module of the Week https://effect.website/blog/module-of-the-week/cluster-messaging post by Maxwell Brown https://x.com/maxwellbrown , diving into Cluster messaging . Effect Cluster, Part 2 - Module of the Week 4 With no coordinator in charge, how does a message find its entity? This week, we define our first entity and follow one message from webhook to punchline 👨 Questions? Office Hours tomorrow, link in 🧵 effect.website/blog/module-of… https://effect.website/blog/module-of-the-week/cluster-messaging/ It has been a week since Effect 4.0 shipped, and the pace has not slowed. According to Sebastian’s post on the first week https://effect.website/blog/effect-4-first-week , almost 30 contributors landed around 150 commits on main , and two patch releases went out: 4.0.1 on October 5 and 4.0.2 on October 8. Here are the most notable changes. - Stability tags : Every module and importable export now declares its @stability level explicitly, enforced by automated checks in the pipeline. 4.0.2 also adds the tags that were missing from some modules intended to ship as unstable. Nothing changes in your code: no behavior, signatures or types are affected. The Effect language service builds on these tags to warn you when you use unstable or experimental APIs. Sebastian’s post has the full story. - OpenTelemetry alignment : Aligned HTTP, SQL and AI spans with the OpenTelemetry semantic conventions, and brought the OTLP exporter, resource and logger in line with the OpenTelemetry spec. Also preserved active OpenTelemetry parents for Effect spans, left interrupted spans unset, and fixed B3 sampling and zero W3C IDs in HTTP trace context. - Additions : Added a DatagramSocket UDP module, PowerShell support for --completions , a delay option on PersistedQueue.offer , a deterministic TestCrypto layer, a noFollow open option and positional reads for FileSystem , compact JSON and inspect output for SchemaError , and more atom registry APIs. - Cluster & workflow : Fixed orphaned workflow activity recovery after a crash, fixed entity recovery when replayed requests defect during handler rebuild, and avoided workflow replay for self-completed checkpoints. WithTransaction replies are now delivered once the transaction outcome is known, with failure replies persisted after rollback. Cluster SQL storage can now run without runtime DDL, and HashRing.getShards no longer depends on node history. - HTTP, MCP & OpenAPI : Preserved query strings during router slash normalization, fixed HttpApi form and GET payloads rejecting single-value arrays, fixed HttpStaticServer If-Range validation, and fixed OpenAPI client response inference. On the MCP side, interrupted reverse requests now send cancellation notifications, cancelled HTTP request POSTs get an empty event stream, and stateful extension capabilities are preserved. - Streams, SQL & AI : Fixed Stream.slidingSize dropping elements from the final partial window, Stream.throttle exceeding its configured rate, and several tapSink edge cases. Fixed typed SQL transaction COMMIT error recovery and MSSQL pool recovery. Fixed Anthropic streamed tool JSON errors, and cached per-tool response schemas for better AI performance. - Continued audit : The correctness audit carried on after the release, with targeted fixes across STM transactions, PubSub , Queue , Pool , Channel , ScopedCache , Layer , ManagedRuntime and Schema union parsing, covering edge cases around interruption, shutdown, retries and resource cleanup. - Config, Schema & docs : Kept = inside values when decoding key-value config strings, canonicalized imported JSON Schema pattern sources, and fixed zoned DateTime when Intl omits fractional seconds. Migration guidance now notes the v4 decoding change in NumberFromString and points parseJson users to fromJsonString Schema.Unknown . You can follow the full changelog in the effect repository https://github.com/Effect-TS/effect/commits/main . To catch up on more updates, check out Effect v4 Updates https://www.effect.website/blog?category=effect-v4-updates , starting from the recently published Effect v4 RC: September 2026 Updates https://effect.website/blog/effect-v4-rc-september-recap . - Effect Paris 🇫🇷 https://www.meetup.com/effect-paris/events/316600366/ meetup is scheduled for Tuesday, Oct 13 Back to @EffectTS https://twitter.com/EffectTS community work in Paris next Tuesday with the 7th edition The edition will probably be the first one ever recorded in Paris thanks to Inato folks 🔥🎥 Rendez-vous 7pm at @EvrygDotCom https://twitter.com/EvrygDotCom , 4 great speakers, 4 great talks ahead Registration link in comment 👇 - Effect Warsaw 2 https://luma.com/k5o7m2pg is coming 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 https://luma.com/k5o7m2pg - Very few 2-day passes left for Effect Days 2026 https://effect.website/effect-days The conference is scheduled for December 9–11 in Livorno, Italy.I’m so happy to share that I’ve received the loveliest invitation to give a talk on @EffectTS https://twitter.com/EffectTS day My lawyers assured me that once my picture is on their page, revoking the invitation is actually illegal. See you there, and please only ask questions I know the answers to, - Any Effecter in Boston? @EffectTS https://twitter.com/EffectTS Boston meetup? ? Would love to make it happen. If you’re in Greater Boston and would come or know of companies in Boston using Effect I can reach out to , reply or DM me so I can get a sense of whether there’s enough interest. - Effect Office Hours 🔥 every Wednesday at 10:00 AM ET / 16:00 CET on our YouTube channel https://www.youtube.com/@effect-ts . Visit our Effect Community Events calendar https://luma.com/effect-community and subscribe for updates on upcoming Effect events. 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 https://twitter.com/EffectfulTech , creators of @EffectTS https://twitter.com/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 - Effect 4.0 Just Got a Lot Harder to Ignore by Better Stack. Play https://youtube.com/watch?v=OsL9EJWz9UY - …or the new @xstate/effect package https://stately.ai/docs/xstate/v6/effect/quick-start Replying to @vkryukov https://twitter.com/vkryukov/status/2107920576048431503 well you can also think of it as token efficiency. for example if your agents can’t verify their work, chances are there will be a lot of bugs and rework that needs to happen later, which also requires more tokens and unhappy customers there’s also many ways to improve ttr - Alchemy 🤍 Effect New alchemy is on Effect 4.0 stable and has too many awesome changes to fit into a single tweet. My favorite this time round is that @neondatabase https://twitter.com/neondatabase is no longer just a database company. It might be time to update their twitter handle 😅 alchemy@2.0.0-beta.80 brings a ton of new stuff, including broad GCP coverage, Neon becomes more than a Database, pluggable secret providers, Prisma ORM, better scheduling primitives for Durable Objects and much more. alchemy.run/blog/2026-09-2… @alchemy run https://twitter.com/alchemy run v2 + @EffectTS https://twitter.com/EffectTS v4 is an incredible combo for infra-as-code biggest shocker: new frameworks and tools can be sooo much better than existing SotA/SoP that agents perform better with something not in pretraining than with "industry standards" well freaking done We all know that the @foldkit, @alchemy run, @EffectTS , and @Cloudflare stack is GOATed but what name should we give it? Reply with your own suggestions - Effect agent frameworks: we dont do a good job of talking about it but @0xblacklight https://twitter.com/0xblacklight built a dope effectTS agent harness that 1 stores state as a portable append only log 2 runs on durable objects out of the box 3 has cool retro opentui UI with 10 themes three Effect agent frameworks worth checking out: - Fold by @0xblacklight - Yielded Agent by @danieljvdm - Tardigrade by @arjunkmrm particularly interesting to see they all support cloudflare durable objects as host and worth asking an agent to talk you through their - 👀 Replying to @theo https://twitter.com/theo/status/2107781364607226227 Did it. Effect plugin included too, so no more patch packaging : x.com/theo/status/21… https://x.com/theo/status/2107789940482621795 Announcing tsc-rs aka ts-rust , my complete rewrite of the Typescript compiler, type checker, and LSP, all in Rust. This is a project I've had agents working on for 5 months now. I burned ~$400k of Codex tokens and got nowhere. Burned ~$20k of Opus and got there in 2 weeks. I - Congrats, Tanner and the Vitalize team We raised a 31M Series A at @vitalize care https://twitter.com/vitalize care We're tackling a critical problem with staffing in healthcare If you want to work with @EffectTS https://twitter.com/EffectTS and clusters at scale, @bunjavascript https://twitter.com/bunjavascript , @tan stack https://twitter.com/tan stack router/query, and @PlanetScale https://twitter.com/PlanetScale Postgres, DM me SF hybrid. - 💯 Replying to @thefubhy https://twitter.com/thefubhy/status/2107356300023615881 Instead of counter measure, we created better tools for the maintainers to triage, recycle and crunch through submissions. Productivity is through the roof, engagement with the community/contributors too and @EffectTS https://twitter.com/EffectTS is ultimately better thanks to it. TL;DR: Improve your - Effect is obviously the solution 😎 Effect is obviously the solution and i know literally no one likes writing yield but it is 2026 and you don’t have to write it yourself rust never was the defacto language for agents and will not be. i love rust - it’s my primary language - but i work on runtimes and platforms application code belongs in the default language - JavaScript or its extension TS - Effect mentioned at 36:18 . Play https://youtube.com/watch?v=HuJB97hUPWk - effect-uai https://effect-uai.betalyra.com/ is now on Effect 4.0. - Changes to STM in Effect 4 https://dev.to/khraks mamtsov/changes-to-stm-in-effect-4-33c3 blog post by Max Khramtsov. - Structure an Effect codebase by domain https://ratstack.sh/lore/structure-effect-by-domain - a guide on organizing Effect codebases by domain. By RatStack. - effect-harness https://github.com/julia-script/effect-harness - durable AI conversations built with Effect. By Julia Ortiz. - effect-atom-svelte https://github.com/jarrednorrisdev/effect-atom-svelte - Svelte 5 bindings for Effect Atom. By Jarred Norris. - ensforge https://ensforge.com/migrations/overview - an ENS SDK that has just released 0.6.0, updated to Effect 4.0. By The Namespace. - opfs-vfs https://github.com/opfs-vfs/opfs-vfs - a virtual filesystem for the Origin Private File System OPFS . - openchart https://github.com/longsurf-ai/openchart - an open-source TradingView alternative with your own AI, free and unlimited. By longsurf.ai. - effectlings https://github.com/stardazed/effectlings - small exercises that teach Effect v4, one idea at a time. By stardazed. Don’t forget to listen to our Cause & Effect podcast hosted by Johannes Schickling and available on YouTube https://www.youtube.com/@effect-ts , X Twitter https://x.com/EffectTS /status/2085682364315783506 , and audio platforms like Spotify https://open.spotify.com/episode/12L2neeIte6LUYQpzTh9n6 and Apple Podcast https://podcasts.apple.com/us/podcast/software-engineering-in-the-age-of-ai-10/id1781879869?i=1000780438320 . John A. De Goes, the creator of ZIO https://zio.dev/ , as well as CEO of Ziverge https://www.ziverge.com/ and Golem Cloud https://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 https://youtube.com/watch?v=irmz5X3c7Do - Effect Office Hours 49 🔥 Play https://youtube.com/watch?v=dlbrbz3KW40 - Local Telemetry, Grafana LGTM, Motel, and Effect v4 Tracing Play https://youtube.com/watch?v=R7kjeiQXQOE - Effect Cluster, Part 1 | Module of the Week 3 Play https://youtube.com/watch?v=TB145FAQnDM - Effect Cluster, Part 2 | Module of the Week 4 Play https://youtube.com/watch?v=9QDcO50YriA 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 → 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. The Effect Merch Store https://effect.website/merch offers a selection of Effect-branded items designed for the community. All orders are processed and fully managed through Printful https://www.printful.com/ . 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 https://effect.website/merch 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 Effect 4.0: The First Week https://effect.website/blog/effect-4-first-week