# Size availability gate — dev spec
Site: allbirds.com · Priority 8 · High · Effort: Medium (2-5 days)

## Problem
Product pages show a 'Get Notified' CTA for out-of-stock sizes, but the size selector is present, creating a potential expectation that all sizes are available when they are not.

## Evidence (from the live site)
> On /products/anytime-ankle-sock, the CTA 'Get Notified' appears, and the page has a size selector (direct_signals: size_selector: true). The body_sample includes 'Get Notified' but no explicit 'Out of Stock' messaging near the size selector.

## Current state
h1: Anytime Ankle Sock; cta: Get Notified; notes: Size selector present but some sizes may be unavailable, leading to 'Get Notified' instead of 'Add to Cart'.

## Required change
h1: Anytime Ankle Sock; cta: Add to Cart; notes: Clearly mark out-of-stock sizes with 'Out of Stock' and disable them, or show 'Get Notified' only for those sizes, to avoid confusion.

## Acceptance criteria
- GIVEN a first-time visitor on the affected page
- WHEN the change is live
- THEN Clearly mark out-of-stock sizes with 'Out of Stock' and disable them, or show 'Get Notified' only for those sizes, to avoid confusion.
- AND no layout regression at 375px / 768px / 1280px
- AND the changed control is keyboard-reachable with an accessible name

## Tracking
- Fire `cro_size_availability_gate` on interaction with the changed element
- Verify the event fires in BOTH variants before opening traffic

## Test plan
- Two-proportion z-test, 95% significance, 80% power
- 299,882 visitors per variant to detect a 5.0% relative lift
- Run at least one full business cycle; not testable at current traffic

## Rollback
Feature-flag the change; revert if the primary metric drops for 3 consecutive days.