Today, we’re releasing Effect 4.0. It’s the most ambitious release we’ve ever shipped. We rebuilt Effect from the ground up. It’s faster, uses a fraction of the memory, and tree-shakes to far smaller bundles. Bundle size dropped from 35.6 kB to 7.1 kB. Concurrent task throughput increased 6.4× to 4.57M tasks per second. Memory per fiber decreased 86% to 21.8 MB for 50,000 fibers.
One ecosystem, zero dependencies. Many previously separate packages now live in effect itself. The core effect package has zero runtime dependencies. We control every line we ship, so there are no third-party dependency chains and less exposure to supply chain attacks.
From functions to clusters. Effect now covers the full range, from a single function to a distributed system. The standard library and platform integrations grew around it. Higher-level primitives for distributed systems include durable workflows and clustering.
Mainstream adoption. Weekly npm downloads reached 43.9M in the week of September 21, 2026, growth of 179× since 3.x. 4.x adoption already outsizes 3.x. Long-term support for Effect 4.x: bug fixes until September 2029, or one year after 5.0 ships, whichever is later.
Source: Hacker News · Summarized by HeadlinesBriefing