ACF Tip of the Month – May 2026: Opt Into ACF Blocks V3 for Cleaner Block Previews

If you’re building custom blocks with ACF Pro and still haven’t switched to Block Version 3, this month’s tip is for you. One line in your block.json is all it takes to address one of the most common pain points with ACF Blocks — style conflicts between the WP admin UI and your block’s preview.

The Problem: Style Bleed in Block Previews

Before ACF Blocks V3, ACF block editing relied on the older inline editing experience. That meant your block’s frontend CSS could mix with WordPress admin styles — buttons looked wrong, typography rules collided, layout broke. You’d build something that looked fine on the frontend but was a mess in the editor.

ACF Blocks V3 aligns with WordPress’s iframe-based block rendering architecture. This greatly reduces style conflicts between editor UI styles and your block preview, making what you see in the editor far closer to the frontend result.

How to Enable It

Open your block’s block.json and add the acf key:

{
    "name": "acf/my-block",
    "title": "My Block",
    "description": "A custom ACF block.",
    "acf": {
        "blockVersion": 3
    }
}

That’s the entire change. Most blocks can migrate without PHP or JavaScript changes.

V3 is opt-in per block, so existing blocks on your site aren’t affected until you add that line. You can migrate one block at a time and test before touching the rest.

What Changes in the Editor

With V3 enabled, ACF opens a dedicated expanded editor panel for your block’s fields. Instead of the fields squeezing into the sidebar, you get a full-width editing interface. The block preview itself stays in the canvas — you’re no longer replacing the preview with a form.

You can also add "hideFieldsInSidebar": true in the acf key (added in ACF 6.6.2) if you want to suppress the sidebar fields form entirely and keep editors focused on the expanded panel:

"acf": {
    "blockVersion": 3,
    "hideFieldsInSidebar": true
}

Requirements

• ACF Pro (Blocks are a Pro feature)
• WordPress 6.2 or higher (required for the iframe APIs V3 relies on)
• ACF 6.6 or higher

If you’re on older versions, update ACF first — the blockVersion key is silently ignored on older releases.

Why Do This Now

WordPress core is moving toward iframe-based block rendering for all blocks. V3 aligns your ACF blocks with where the platform is heading. Inline editing support arrived in ACF 6.7 and is available only for V3 blocks so staying on V2 means missing out on that capability entirely.

Migrating now helps prepare your blocks for the future direction of WordPress and ACF Blocks.

One line of JSON. Cleaner previews. Future-proof blocks. If you’re building ACF blocks on any active project, this is worth five minutes of your time today.