---
description: With the introduction of FinalizationRegistry in Workers Runtime, toolchains like Emscripten and wasm-bindgen can automatically reclaim unused WebAssembly heap and reduce memory leaks.
title: Improved memory efficiency for WebAssembly Workers
image: https://developers.cloudflare.com/changelog/post/2025-05-08-finalization-registry/og.png?v=64aba4c20c5a8cca
---

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May 8, 2025

## Improved memory efficiency for WebAssembly Workers

[Workers](https://developers.cloudflare.com/workers/)

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[FinalizationRegistry ↗︎](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/FinalizationRegistry) is now available in Workers. You can opt-in using the [`enable_weak_ref`](https://developers.cloudflare.com/workers/configuration/compatibility-flags/#enable-finalizationregistry-and-weakref) compatibility flag.

This can reduce memory leaks when using WebAssembly-based Workers, which includes [Python Workers](https://developers.cloudflare.com/workers/languages/python/) and [Rust Workers](https://developers.cloudflare.com/workers/languages/rust/). The FinalizationRegistry works by enabling toolchains such as [Emscripten ↗︎](https://emscripten.org/) and [wasm-bindgen ↗︎](https://wasm-bindgen.github.io/wasm-bindgen/) to automatically free WebAssembly heap allocations. If you are using WASM and seeing Exceeded Memory errors and cannot determine a cause using [memory profiling](https://developers.cloudflare.com/workers/observability/dev-tools/memory-usage/), you may want to enable the FinalizationRegistry.

For more information refer to the [`enable_weak_ref`](https://developers.cloudflare.com/workers/configuration/compatibility-flags/#enable-finalizationregistry-and-weakref) compatibility flag documentation.

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