October 12, 2026 · Ahmed · More by Ahmed
What Gets Your Shopify Bundle-Size Exception Denied
Shopify's new bundle-size exception process spells out exactly which causes of UI extension bloat get approved — and which get an automatic no.
The 64 KB limit, with one exception
UI extensions — checkout, customer account, admin, and POS — have run on Remote DOM since API version 2025-10, and that runtime caps each extension's compressed JavaScript bundle at 64 KB, enforced per extension at deploy time. Full-page customer account extensions get 128 KB instead, for a specific structural reason: a full-page target can't be combined with any other target in the same extension, so it always ships alone in its own bundle and gets that bundle's limit to itself.
On September 17, 2026, Shopify published a formal process for apps that are still over budget after optimizing: run shopify app build, then submit the minified bundle plus its esbuild metafile through the bundle size exception form for review.
What gets a request denied
The announcement is specific about this, which is the useful part for a developer deciding whether to file a request or go back and refactor. Shopify will deny exceptions caused by avoidable bundle weight, and names three examples directly: heavy libraries, duplicate dependencies, and translations bundled into the extension instead of served through the surface's native localization APIs. None of those require a platform exception — they're fixable in the codebase, and Shopify's optimize-bundle-size guide lists the swaps: preact over react, date-fns with per-function imports over moment, the built-in fetch over axios, the Web Crypto API over crypto-js.
What actually qualifies
Exceptions are reserved for extensions that are still over the limit after that avoidable bloat has genuinely been removed — where the remaining weight reflects real feature density or a platform gap that doesn't yet have a native alternative. In other words, "we're over the limit" isn't a request on its own; the request has to demonstrate that the easy fixes already happened. Shopify's own guidance treats measurement as a prerequisite, not optional: regenerate the esbuild metafile after each change and check which modules actually contribute size before concluding an extension needs an exception at all.
The deadline in the same announcement
Separately from the exception process, every existing UI extension has to be upgraded to API version 2026-01 or later to remain deployable after October 1, 2026 — that requirement applies regardless of whether an exception is granted or even needed. Worth checking on its own timeline if you haven't audited extension API versions recently.