Platform change Automation and permissions Do this before August 31, 2026

The August 31, 2026 cart deadline has passed. Did it affect my store?

Shopify's maintenance window for two old Storefront MCP cart tools ended. The docs still list them. Ask the integration owner for evidence.

· Updated September 11, 2026

When this applies
A developer or vendor quoted cart migration work for the August 31, 2026 deadline, or a test cart lost line items after an update. [1]
When this does not apply
Take no migration action when no custom agent integration calls Storefront MCP get_cart or update_cart; standard Shopify storefront behavior was never inside this deprecation. [1]
Why this matters
Shopify's stated maintenance window for the deprecated tools ended on August 31, 2026. An unmigrated cart integration now runs with no stated support boundary. [1] [2]
What to do, or not do
Ask the integration owner whether the app still calls get_cart or update_cart at the Storefront MCP endpoint. If it does, require the migration and a passed full-cart test now, not before a date that has gone. [1] [2]
What you'll see when it's done
You hold written evidence that no old get_cart or update_cart calls remain and that full-cart behavior passes on the Cart MCP endpoint, or confirmation that the store has no affected integration. [1] [2]
What this result does not prove
A code inventory and a passing test do not guarantee uptime or live orders, and Shopify has published neither a shutdown time nor a removal notice on the Storefront MCP tools. [1] [3]
Sources checked
September 11, 2026
Changed
June 24, 2026
Deadline
August 31, 2026

When a third party is worth paying for, and what you do not have to buy

When paid help is worth it
Paid help is worth it only when a custom shopping agent you own still calls the deprecated cart tools, and its developer has to migrate and verify it. [1] [2]
What you do not have to buy
Shopify publishes the deprecation, the elapsed date, and the replacement cart tools, so learning about this is not a monitoring product to buy. [1] [2]

You may have received a migration estimate from a shopping-agent vendor, or a test cart may have lost line items after an update. This was a technical deadline for the person or team that maintains a custom agent integration. It was never a setup task for a merchant using Shopify’s standard storefront and admin.

Shopify deprecated get_cart and update_cart on the Storefront MCP endpoint in favour of its UCP-conforming Cart MCP tools. The June 24, 2026 changelog said the deprecated tools would be maintained until August 31, 2026. That date has passed.

What the documentation shows on September 11, 2026 is narrower than a shutdown. Shopify’s Storefront MCP documentation still lists get_cart, update_cart, and search_shop_policies_and_faqs as the standard tools on /api/mcp, with no removal notice, and no later changelog entry extended or retracted the date. The supported statement is that the maintenance window closed and the replacement is Cart MCP. Nobody should tell a merchant the old tools stopped working.

What changed

The deprecated calls use:

https://{shop}.myshopify.com/api/mcp

The replacement Cart MCP tools use:

https://{shop-domain}/api/ucp/mcp

Shopify supplies create_cart, get_cart, update_cart, and cancel_cart at the replacement endpoint. Shopify’s Cart MCP documentation states that Cart MCP implements the UCP cart capability dev.ucp.shopping.cart at version 2026-08-25. The June 2026 announcement named 2026-04-08, so an integration written from the announcement should be checked against the current schemas rather than against the announcement text.

What the integration owner needed to change

Shopify’s migration instructions require more than an endpoint swap:

  1. Move get_cart and update_cart calls to Cart MCP.
  2. Send a meta object in every request, carrying ucp-agent with the agent’s UCP profile URI for capability negotiation.
  3. Send a UUID in meta["idempotency-key"] for cancel_cart.
  4. Treat update_cart as a full replacement. It uses PUT semantics, each request replaces the cart’s whole state, an omitted field is removed, and there is no server-side merge.
  5. Validate the integration against the current request and response schemas in Shopify’s Cart MCP documentation.

The full-replacement behavior is the main regression risk. Code that sends one changed line item as a patch can discard the rest of the cart when moved without adjusting its request construction. Attribution sits inside the same trap: because the cart object is replaced, attribution has to be resent on every update to survive it.

What evidence the merchant should request

A merchant using only Shopify’s standard storefront and admin has no migration step. A merchant using a custom shopping agent, assistant, or integration should ask the person or team that maintains it for two artifacts, dated now rather than promised against a date that has gone:

  • An endpoint and tool inventory confirming whether any get_cart or update_cart call still targets /api/mcp.
  • A dated test record showing add, update, remove, and cancel on Cart MCP plus the handoff to Checkout MCP, including a multi-line cart that keeps every unmodified line.

The observable result is written confirmation that no old calls remain and the full-cart test passes, or confirmation that the store has no affected integration. This evidence does not guarantee uptime or live orders. Shopify stated the end of maintenance and has published no shutdown time.

Sources

  1. Storefront MCP cart tools deprecation
  2. Cart MCP
  3. Storefront MCP server