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This Week in Effect - #122

Intro to Effect Miami, by Ariel Azoulay. Effect Milan meetup hosted by Datapizza. v4 Beta: tree-shaking, Schema fixes & a key Entity reliability fix.

Davide Scognamiglio Davide Scognamiglio Project Manager Mirela Prifti Mirela Prifti Community Manager Michael Arnaldi Michael Arnaldi BDFL

Hi Effecters!

Welcome back to This Week In Effect (TWIE) - your weekly update of the latest developments in the Effect community and ecosystem.

Effect is a powerful TypeScript library that helps 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

Effect v4 Beta updates

The v4 beta had a well-rounded week, with important bug fixes across Schema, tree-shaking improvements, AI provider updates, and a significant Entity reliability fix — here are the most notable changes that landed in effect-smol.

  • Tree-shaking: Made module-level side effects in effect tree-shakable, reducing bundle sizes for applications that only import a subset of the library.

  • Schema fixes: Fixed schema encoding checks and index signatures, fixed Schema.encodeKeys property key handling, fixed ObjectKeyword JSON Schema output, and fixed fractional duration rounding to be symmetric when normalizing to nanoseconds.

  • Arbitrary generation: Refactored the arbitrary generation engine and made BigDecimal range generation scale-aware, using generic ordered constraints for more accurate schema-derived test data.

  • HTTP & HttpApi: Encoded HTTP API path params correctly for non-string types, and fixed Random.withSeed string seed encoding.

  • Entity reliability: Fixed EntityManager defect restarts so in-flight requests are replayed rather than dropped when the old entity scope is interrupted — a significant correctness fix for long-running entity workflows.

  • AI providers: Fixed Claude 4 generation to support native structured output in ai-anthropic, fixed null function.name handling on streamed tool-call fragments in ai-openai-compat, and declared the missing swagger2openapi runtime dependency in the OpenAPI generator.

  • RateLimiter: Added TTL and nil-guard to the Redis token-bucket implementation to prevent stale state accumulation.

  • Graph: Fixed undirected graph traversal logic.

  • CLI: Added metavar/log-level meta support to show values for log level arguments.

  • Documentation: Clarified Effect.fn and fnUntraced usage, clarified Model.GeneratedByDb variants, fixed the MCP example in effect docs, corrected JSDoc on Workflow.poll and WorkflowEngine.poll, and continued the module JSDoc refactor.

Full changelog in the effect-smol repository.

You can find a recap of all Effect v4 Beta updates from launch to May, organized by topic, so you can jump straight to what matters most to you.

 

Here are all the technical changes from the past week.

Effect Core

Effect Platform

 

Community Events

Thank you to Datapizza for hosting the Effect Milan meetup this week. Looking forward to many more events together! 🙌 🍕

Stefan ⚛︎ 🎆
Stefan ⚛︎ 🎆
@stefangarofalo
· Follow

“Effect code tends to be verbose, but that’s not necessarily a bad thing for your agent” Your DX depends now heavily on AX. Treat your agent well. Prioritise it over your own coding taste

Image
Effect | TypeScript for the AI Era
Effect | TypeScript for the AI Era
@EffectTS_

Effect Milan 🇮🇹 is happening today! Hosted by Datapizza! Speakers: @leo_trapani - Founding Engineer @ Datapizza ​ @MattiaManzati - Effect Core contributor, Founding Engineer @EffectfulTech luma.com/yirm3nb7

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Visit our Effect Community Events calendar and subscribe for updates on upcoming Effect events.

 

Community Highlights

 

 

  • Effect http client is really good 😎

    Ben Davis
    Ben Davis
    @davis7
    · Follow

    100% the effect http client is really good, and now that models are writing most of the code there's a lot of stuff like this that would've been annoying before Cloudflare is another great example of something too annoying before that I'm starting to heavily use

    Image
    stibbs
    stibbs
    @MatthewStibbard

    Can you get all the benefits of effect using it with svelte/sveltekit?

    180
    Reply
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  • ax - an Effect-powered, local-first observability and memory layer for AI coding agents (Claude Code, Codex) that learns from your sessions to surface repeated mistakes and suggest repo-specific improvements.

 

  • Slashspace AI - a canvas-first desktop app for sustained AI work, where you create spaces with multiple agents that share context, run in parallel, and access connected tools, with everything stored locally as files. Built with Effect on the backend.

 

  • effect-bdd - an Effect-native runner for Gherkin .feature files.

 

 

Effect Content Update

  • Effect Office Hours 32 🔥
Play

 

  • Intro to Effect Miami | Ariel Azoulay | Effect Miami 🇺🇸 2026
Play

 

  • When should you use Effect.die instead of Effect.fail
Play

 

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.

Adam Rankin, CTO at Warp, joined Johannes Schickling to talk about using Effect to bring structure and composability to a growing TypeScript codebase, enabling a small, fast-moving team to stay productive while shipping reliable payment & payroll systems.

Play

 

Effect Job Opportunities

More and more companies are adopting Effect in their projects. Here’s a list of companies looking for software engineers with Effect experience:

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.

 

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

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