Tailwind 4.3.5 fixes only the problems you hit after months of use: color-mix crashes, WASM hangs, slow canonicalization

Tailwind shipped 4.3.5 on November 6. A patch release with no feature announcements. I enjoyed reading the fix list, because every line sounds like it was pulled out of somebody’s issue rather than a press release about developer experience.

color-mix without an interpolation method crashed

The CSS syntax is color-mix(in oklab, red 50%, blue). If you wrote color-mix(var(--color-red-500)) or color-mix(currentcolor 50%, transparent), meaning no interpolation method, Tailwind used to crash or emit a fallback with the wrong colour.

The frightening part of this bug is how quiet it is. The build passes, the page renders, the colour is just slightly wrong, and then a design review asks whether that grey is a mistake.

The WASI build could hang forever

Second: @tailwindcss/oxide-wasm32-wasi used to hang forever, particularly with NAPI_RS_FORCE_WASI=error or in WebContainers. It now loads. The same release fixes it failing to detect changed and new source files after the first scan.

WebContainers deserve a note: running Node in the browser is how many people edit a demo from a link. A build tool hanging there cuts off an entire learning path.

Thousands of variant values no longer slow canonicalization

Third is performance: projects with many functional variant values, such as a matchVariant plugin carrying thousands of values, saw canonicalization slow down noticeably.

I have seen this in real design systems: spacing, radii and layers all expressed as matchVariant, with tables hundreds of lines long. Nobody notices in development until HMR starts to stutter and someone finally profiles it.

Two more obscure but useful fixes

• <!-- and --> between top-level rules are ignored instead of throwing or swallowing the next rule (a { color: red } --> b { color: blue })
• as: '*.css' is gone from the @tailwindcss/turbopack README, because that line breaks CSS Modules

Why write about a small patch

Because a patch release’s fix list is the most honest engineering record there is. Feature releases tell you what a team wants to do. Patch notes tell you what users actually ran into.

The three things users ran into here, wrong colours, hung builds, slow generation, cover the three classic failure modes of a CSS toolchain: correctness, availability, performance. All of them are the kind that never reproduce on your machine and happen daily in someone else’s project.

So my advice is dull: upgrade. 4.3.5 adds no syntax and breaks nothing. It closes holes that should have been closed earlier.