November 10, 2025 · reala11y team

WCAG 3.0 and APCA: the future contrast model, explained

WCAG 3.0 is an early W3C draft and APCA is its candidate contrast method. How it differs from 1.4.3, why it's not a target yet, and what to actually do today.

Every few months, a design tool ships an “APCA contrast” readout and someone asks whether the contrast rules just changed. They didn’t. APCA and the broader WCAG 3.0 effort are real, genuinely interesting, and worth watching — but WCAG 3.0 remains an early W3C draft, and the contrast standard you build to today is still WCAG 2.x’s 1.4.3. This post explains the difference so you can read the headlines without acting on them prematurely.

What WCAG 3.0 is (and isn’t)

WCAG 3.0 — the “W3C Accessibility Guidelines,” same acronym, different expansion — is a ground-up rethink of how accessibility guidance is structured. Instead of pass/fail success criteria grouped under the familiar Perceivable / Operable / Understandable / Robust principles, it proposes outcomes, scored tests, and a graded conformance model (bronze / silver / gold).

The crucial status point: WCAG 3.0 is a W3C Working Draft. It is not a Recommendation, it has no stable conformance model, and the W3C itself has said it’s years from completion. By contrast, WCAG 2.2 became a W3C Recommendation on 5 October 2023 and is what regulations and procurement actually reference. WCAG 2.x is not being retired any time soon; 3.0 is being built alongside it.

So treat WCAG 3.0 the way you’d treat a draft spec in any field: read it, learn from its direction, but don’t refactor your site to chase a moving target.

How APCA differs from 1.4.3

APCA — the Advanced Perceptual Contrast Algorithm — is the contrast method being explored for WCAG 3.0. It matters because the current 1.4.3 contrast formula has known shortcomings, and APCA is an attempt to fix them.

The differences are substantive:

• Different math. WCAG 2.x contrast is a ratio (e.g. 4.5:1) derived from relative luminance. APCA produces a lightness contrast value (Lc) on a scale running roughly from -108 to 108, based on a perceptual model of how the human eye actually reads text.
• Direction matters. In the 2.x ratio, light-on-dark and dark-on-light with the same two colours yield the same number. APCA treats them differently, because polarity genuinely affects readability.
• Size and weight are built in. 1.4.3 has a blunt two-tier rule: 4.5:1 for normal text, 3:1 for “large” text. APCA ties the required contrast to font size and weight on a sliding scale — thin text needs more contrast, bold display text needs less.

In practice, APCA tends to be stricter about light grey body text (the kind of low-contrast type that’s everywhere and that 1.4.3 sometimes lets slide) and more forgiving about large bold headings. That’s a more honest model of readability. But “more honest” is not the same as “the standard,” and the two methods don’t map cleanly onto each other — you can’t convert a 4.5:1 ratio into an Lc value with a simple formula.

Why you shouldn’t target APCA yet

It’s tempting to adopt the better model early. Resist it, for concrete reasons:

• It’s still a draft. APCA’s thresholds and even its bronze/silver/gold framing have shifted across drafts and could shift again. Building to a number that may change is wasted work.
• Regulations point at 2.x. The US DOJ’s ADA Title II rule names WCAG 2.1 AA. The European Accessibility Act’s harmonised standard (EN 301 549) tracks WCAG 2.x. Section 508 references WCAG 2.0 AA. None of them reference APCA. If you’re meeting an obligation, 1.4.3 is the criterion that counts.
• Tooling and audits expect ratios. Your auditor, your scanner, and most of your team’s mental model run on contrast ratios. Switching to Lc internally before the ecosystem does invites confusion.

What to actually do today

The pragmatic stance is “build to 1.4.3, glance at APCA”:

• Conform to WCAG 2.x contrast now. 4.5:1 for normal text, 3:1 for large text (≥ 24px, or ≥ 18.66px bold) and for UI component boundaries (1.4.11). That’s the bar that satisfies current regulations and audits.
• Use APCA as a tie-breaker, not a target. If two palettes both pass 1.4.3, the one with the stronger APCA reading is probably the more readable choice. It’s a useful design signal — just not a conformance claim.
• Avoid the grey-text trap regardless. The body text APCA is strictest about — light grey on white — is worth fixing under either model. If your theme’s muted text is borderline at 4.5:1, darken it. You’ll satisfy 1.4.3 and APCA at once.
• Don’t relax headings just because APCA would. Until 3.0 is a Recommendation, large low-contrast headings that fail 1.4.3 still fail the standard you’re held to.

For WordPress specifically, this lands in theme.json and your design tokens. Set body-text and link colours that clear 4.5:1 against their real backgrounds, and check them in context rather than trusting a swatch — a colour that passes on white can fail on a tinted section.

Where tooling fits

Automated contrast checking is one of the few places automation is genuinely strong: it’s pure math against the rendered colours, and contrast is among the highest-volume issues on the web. reala11y checks contrast against the current WCAG 2.x thresholds and helps your site move toward WCAG 2.2 AA conformance — the standard that’s actually in force.

We’re not shipping APCA scoring as a conformance check, and that’s deliberate: presenting a draft method as a pass/fail gate would mislead. Even on contrast, the honest caveat holds — automated tooling, ours included, detects roughly 30–40% of WCAG issues by criteria; whether a low-contrast value is on decorative text or critical content still takes a human eye.

The honest takeaway

WCAG 3.0 and APCA are the future of contrast, and the future is worth understanding — APCA models real readability better than a flat ratio does. But it’s a draft to watch, not a standard to target. Build to WCAG 2.x’s 1.4.3 today, use APCA as a design tie-breaker, fix low-contrast grey text under either model, and revisit when 3.0 actually reaches Recommendation. For the contrast rules in force right now, see our colour contrast guide and the WCAG 2.2 reference.