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This Week in Effect - 137

Module of the Week 2: RcMap. Effect v4 RC lands a major runtime performance pass across Schema, Queue, Stream, and Scope.

Davide Scognamiglio Project Manager Mirela Prifti Community Manager

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.

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 success Exit between continuations, stopped Queue/TxPriorityQueue from doing unnecessary re-sorting and traversal work, stopped MutableList from retaining a slot for every element that ever passed through a never-emptying list, stopped forked Scopes from registering a finalizer just to leave their parent, and fixed Stream.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 every SchemaParser.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: Fixed Queue 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, fixed Layer.MemoMap hanging or leaking a shared layer when a requester is interrupted, and made awaitAllChildren interruptible.

  • New APIs: Added Config.flatMap, added Schema.StringForLiteralAutocomplete, added family-aware NetAddress type helpers, added isPubSub, isTxChunk, and isPlatformError type guards, and added dual forms to several existing APIs.

  • Module reorganization: Moved Arbitrary 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 a previous_response_not_found error, and preserved streamed text and tool arguments for nullable delta role and tool call IDs.

  • Bundle size: Reduced BigDecimal bundle size, and built Mime lookup tables lazily on first use instead of eagerly.

  • Documentation: Clarified JSON Schema decoding with the canonical codec, and refreshed PlatformError 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

Community Events

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!

Community Highlights

  • Okay, say no more, Matthew🤝
  • Can’t wait for the episode to come out!
  • Anyone?
  • Welcome, Fernando!

  • Coach by MasterClass - a real-time professional coaching app from MasterClass, built with Effect in both the Electron app and the backend.

  • 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.

Play

Effect Team Content Update

  • Effect Office Hours 47 🔥
Play
  • Effect-mq: Background jobs for Effect w/ Adam Rankin, Warp CTO.
Play
  • PersistedQueue | Module of the Week #1 by Maxwell Brown.
Play

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.

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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