Legacy checkout.liquid, Order status page additional scripts, and script‑tagged apps are being phased out in favor of Checkout Extensibility. Missing the August 28, 2025 milestone for Plus stores locks legacy Thank you / Order status pages and disables legacy scripts; non‑Plus have until August 26, 2026. Migrations start auto‑upgrading in January 2026 if you don’t act. See Shopify’s official guides for the exact scope and timelines: Upgrade guide (Plus), General upgrade doc and Non‑Plus guide.

Who is this for? Merchants and implementers who need a concrete, low‑risk plan to migrate tracking, upsells, loyalty, surveys, and UI tweaks off legacy methods and onto upgrade‑safe extensions, app blocks, and web pixels. Checkout extensibility overview.

What’s Changing (and Why It Matters)

No more checkout.liquid on Thank you / Order status pages after the deadline; legacy PII access is removed and edits are blocked until you upgrade. Official scope
Additional Scripts box and many script‑tagged app injections are deprecated → replace with app blocks and pixels. Order status page changes
Checkout UI Extensions power upgrade‑safe UI at defined targets across information, shipping, payment, and Shop Pay; most in‑checkout targets are Plus‑only. API
Post‑purchase extensions move upsells off brittle DOM hacks onto supported extension points. Build a post‑purchase offer
Order status page is now extended with app blocks / targets instead of arbitrary scripts. Order status page targets

Executive Timeline & Risk

Plus: Upgrade Thank you / Order status by Aug 28, 2025 (scripts blocked after). Auto‑upgrades begin Jan 2026 if you don’t migrate. Plus upgrade guide.
Non‑Plus: Deadline Aug 26, 2026. Non‑Plus guide.
Earlier milestone (historical): information/shipping/payment moved to extensibility in Aug 2024 for Plus. Background.

Migration Plan (Field‑Tested)

Phase 1: Inventory & Risk Assessment

Create a single spreadsheet of everything touching checkout, post‑purchase, and order status:

Tracking & pixels: GA4, Meta, ad platforms, GTM.
Loyalty, surveys, attribution: Fairing, Enquire, post‑purchase, UTMs.
Upsells & cross‑sells: OCU/Zipify, Rebuy, custom scripts.
UI tweaks: extra fields, content boxes, trust badges.
Subscriptions / payments / discounts: Recharge, Functions.

Mark each item as critical, nice‑to‑have, or remove. Add its replacement path (app block / UI extension / pixel / server event) and an owner.

Tip: Shopify generates a personalized Upgrade Guide in Admin to enumerate customizations and compatible apps. Use it to shorten discovery. Where to find it.

Phase 2: Replacement Paths (Legacy → Extensible)

Additional scripts → Web Pixels & App Pixels: Move measurement to Customer events. Configure server‑side events for ad platforms (e.g., Meta CAPI via Shopify’s Enhanced/Maximum data‑sharing modes). Pixels & customer events · Meta data‑sharing levels.
DOM injections on Thank you / Order status → App blocks: Rebuild with app blocks / targets rather than addContentBox or custom HTML. Order status page targets.
In‑checkout UI code → Checkout UI Extensions (Plus): Use component + target APIs instead of editing templates. Checkout UI extensions API.
Post‑purchase hacks → Post‑purchase extension: Implement supported upsell flows. Post‑purchase overview.
Discount logic in liquid/js → Shopify Functions (Discounts): Implement rules with the Discount Function API.
Subscriptions (Recharge) customizations: Verify checkout‑integration compatibility and move SMS/opt‑ins out of checkout if required. Recharge compatibility notes.

Fast‑path apps: For simple field adds, limits, or method ordering, try Shopify’s Checkout Blocks. Many survey/upsell vendors (Fairing, Rebuy, Zipify OCU) ship compliant app blocks.

Phase 3: Tracking & Attribution (GA4/Meta)

GA4 via Pixel/GTM: Install GA4 using a custom pixel or GTM configured through Customer events (Extensibility). Validate event names and parameters. GA4 via CE/GTM.
Meta Pixel + CAPI: Use Shopify’s Enhanced/Maximum settings to enable Conversions API alongside the pixel for resilient purchase events. Confirm server event receipt in Events Manager. Meta data sharing.
Deduplicate: Ensure event_id/fbp/fbc mapping to avoid double counting. (See vendor‑maintained guides, e.g., Analyzify’s CAPI guide.)
Thank you / Order status events: Recreate purchase/refund events with app pixels and blocks instead of Additional Scripts. Upgrade steps.

Phase 4: Testing Matrix (Don’t Ship Blind)

Test before publish and again after rollout:

Functional: discounts, gift cards, subscriptions, Shop Pay, dynamic shipping/payment options, multi‑currency.
Failure paths: payment decline, stockout after payment, partial capture/refund.
Attribution: GA4 purchase/refund, Meta Purchase CAPI + pixel, deduped counts across browsers and iOS Safari.
Performance: LCP/FID shifts on the information/shipping/payment steps and on Thank you / Order status.
Security & PII: Confirm no deprecated PII access on legacy pages after upgrade.

Use Shopify’s preview + placement references for Order status targets to validate block render positions. Order status targets.

Phase 5: Launch & Monitor

Staged rollout: enable by market/channel → watch revenue & attribution deltas.
Logging: centralize app/pixel errors; alert on attribution drops.
Governance: weekly review of apps/permissions; maintain a change log.
Rollback levers: keep pre‑migration theme/app versions and be ready to disable specific blocks/extensions—not the whole checkout—if a KPI regresses.

Common Pitfalls (and Fixes)

Assuming non‑Plus can use in‑checkout UI targets → many are Plus‑only; move non‑Plus customizations to Thank you / Order status blocks or the Online Store. Plus requirement note.
Trying to keep Additional Scripts → it’s deprecated; move logic to pixels or app blocks. Deprecation context.
Server events not arriving → confirm CAPI status and event match keys; common misconfigs are documented by the community. Example thread.
Post‑purchase hacks → replace with the supported extension to avoid breakage. Post‑purchase extension.

FAQ

Do we lose features in Extensibility? Some bespoke tweaks require app alternatives, but you gain security, performance, Shop Pay compatibility, and upgrade‑safety. Extensibility benefits.

How do we ensure attribution continuity across devices? Use Web/App Pixels and enable server‑side events (CAPI). Validate using Events Manager and GA4 DebugView; set up de‑duplication keys. Pixels & CAPI · Meta settings.

What breaks most often? Legacy DOM hooks and global objects on Thank you / Order status, additional scripts, and post‑purchase hacks; rebuild with blocks, pixels, and extensions. Upgrade steps.

Is there a minimal rollback plan? Keep tagged pre‑migration states; define thresholds that auto‑disable specific extensions/blocks if conversion or pixel integrity drops (don’t revert the whole checkout). General guidance.

Copy‑Paste Checklist

Export the Admin Upgrade Guide list, map each item to: block / UI extension / pixel / function.
Install/enable Checkout Blocks (for simple fields/limits/order).
Rebuild surveys/upsells using vendor app blocks (e.g., Fairing, Rebuy, Zipify OCU).
Move GA4 to Customer events (custom pixel or GTM). Validate with GA4 DebugView. How‑to.
Enable Meta CAPI (Enhanced/Maximum). Verify server events + deduplication. Meta guide.
QA Thank you / Order status events & blocks across browsers; ensure no PII leaks from legacy pages. Scope.
Stage rollout by market; add alerting on KPI deltas.

Related resources

Shopify: Checkout UI extensions · Pixels & customer events · Order status page targets · Post‑purchase extensions.
Practical how‑tos & analysis: Analytics Mania – GA4 via Extensibility, Analyzify – CAPI/Pixel, Digital Position – deadline explainer.

This guide intentionally hyperlinks source phrases (e.g., Upgrade guide, Pixels, UI extensions) so your team can jump straight into the right docs while keeping your checkout upgrade‑safe and measurable.