Your shopping-agent vendor has an August 31 cart deadline
This affects custom agents that call two old Storefront MCP cart tools. Ask the integration owner for an endpoint inventory and passed cart tests.
· UpdatedAugust 22, 2026
The question
Does the August 31 cart deadline affect my store?
- This applies when
- A developer or vendor says your custom shopping agent needs cart migration work before August 31, 2026, or a cart test loses line items after an update. [Source 1]
- Nothing to do right now
- Take no migration action when no custom agent integration calls Storefront MCP get_cart or update_cart; standard Shopify storefront behavior is outside this deprecation. [Source 1]
- Why this matters
- Shopify says the deprecated tools will be maintained only through August 31, 2026. An unmigrated cart integration loses a stated support boundary after that date. [Source 1] [Source 2]
- What to do
- Ask the integration owner whether the app calls get_cart or update_cart at the Storefront MCP endpoint. If it does, require migration and verification before August 31, 2026. [Source 1] [Source 2]
- How to know you're done
- You obtain written evidence that no old get_cart or update_cart calls remain and that full-cart behavior passes on the UCP endpoint, or confirmation that the deadline is irrelevant. [Source 1] [Source 2]
- What this doesn't prove
- A code inventory and passing test do not guarantee post-deadline uptime or live orders, and Shopify has not stated that the old tools will shut down at a specific time. [Source 1]
- Sources checked
- August 22, 2026
- Changed
- June 24, 2026
- Deadline
- August 31, 2026
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 is a technical deadline for the person or team that maintains a custom agent integration. It is not 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 says the deprecated tools will be maintained through August 31, 2026.
This deadline affects integrations that call the old tools. It does not require a standard Shopify merchant to install a new storefront feature. Shopify has not stated what exact failure begins on September 1, so the supported claim is the end of the maintenance window, not a guaranteed shutdown time.
What changes
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. The tools conform to the UCP cart capability identified in Shopify’s documentation as version 2026-04-08.
What the integration owner needs to change
Shopify’s migration instructions require more than an endpoint swap:
- Move
get_cartandupdate_cartcalls to Cart MCP. - Send a
metaobject containingucp-agent.profilewith every request. - Send a UUID in
meta["idempotency-key"]forcancel_cart. - Treat
update_cartas a full replacement. Send the completeline_itemsarray with every update. - 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.
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:
- An endpoint and tool inventory confirming whether any
get_cartorupdate_cartcall 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 post-deadline uptime or live orders. Shopify has stated the end of maintenance, not a specific shutdown time.