diff --git a/pyproject.toml b/pyproject.toml
index 8f8405dd..476c81df 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -25,6 +25,7 @@ markers = [
     "restapi: REST API admin endpoint tests",
     "serial: test mutates global platform state and must not run in parallel",
     "destructive: test restarts or drops global state (restart platform, drop search index). Excluded from default CI runs.",
+    "optional: test belongs to an unstable/optional backend module bundle. Exclude with `-m 'not optional'`.",
     "with_user(username): sign in as the given user for this test",
     "with_page_context(username): provide a Playwright page context for the given user",
     "with_cart(items): seed a cart with the given list of (productId, quantity) pairs",
diff --git a/tests/graphql/test_quote_create.py b/tests/graphql/test_quote_create.py
index 96bc4d76..b420cced 100644
--- a/tests/graphql/test_quote_create.py
+++ b/tests/graphql/test_quote_create.py
@@ -1,5 +1,6 @@
 import allure
 import pytest
+
 from core.clients import GraphQLClient
 from gql.operations import QuoteOperations
 from gql.types import Cart
@@ -10,6 +11,7 @@
 _USERNAME = "acme_store_employee_1@acme.com"
 
 
+@pytest.mark.optional
 @pytest.mark.graphql
 @pytest.mark.with_user(_USERNAME)
 @allure.feature("Quotes (GraphQL)")
@@ -32,6 +34,7 @@ def test_quote_create_empty(graphql_client: GraphQLClient, ctx: Context) -> None
         assert quote.items == []
 
 
+@pytest.mark.optional
 @pytest.mark.graphql
 @pytest.mark.with_user(_USERNAME)
 @pytest.mark.with_cart([(_PRODUCT_ID, _QUANTITY)])
diff --git a/tests/graphql/test_quote_update.py b/tests/graphql/test_quote_update.py
index 59a1eb4b..de07f52b 100644
--- a/tests/graphql/test_quote_update.py
+++ b/tests/graphql/test_quote_update.py
@@ -1,5 +1,6 @@
 import allure
 import pytest
+
 from core.clients import GraphQLClient
 from gql.operations import QuoteOperations
 from gql.types.cart import Cart
@@ -10,6 +11,7 @@
 _UPDATED_COMMENT = "Updated comment"
 
 
+@pytest.mark.optional
 @pytest.mark.graphql
 @pytest.mark.with_user(_USERNAME)
 @pytest.mark.with_cart([(_PRODUCT_ID, 1)])
@@ -34,15 +36,14 @@ def test_quote_update_items(
             quantity=_UPDATED_QUANTITY,
         )
 
-    with allure.step(
-        f"Verify proposal prices include quantity {_UPDATED_QUANTITY}"
-    ):
+    with allure.step(f"Verify proposal prices include quantity {_UPDATED_QUANTITY}"):
         updated_item = next(i for i in updated_quote.items if i.id == line_item.id)
         assert any(
             t.quantity == _UPDATED_QUANTITY for t in updated_item.proposal_prices
         )
 
 
+@pytest.mark.optional
 @pytest.mark.graphql
 @pytest.mark.with_user(_USERNAME)
 @pytest.mark.with_cart([(_PRODUCT_ID, 1)])