diff --git a/pyproject.toml b/pyproject.toml
index fa72313..6a9cb63 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -81,7 +81,8 @@ reportImplicitStringConcatenation = false
 [tool.pytest.ini_options]
 markers = [
     "functional: mark a test as a functional test",
-    "e2e: mark a test as an end-to-end test which asserts expected scores for known inputs. These tests should only be considered authoritative against the live classifier."
+    "e2e: mark a test as an end-to-end test which asserts expected scores for known inputs. These tests should only be considered authoritative against the live classifier.",
+    "soak: mark a test as a soak test that runs many requests over a longer duration to validate stability and performance."
 ]
 addopts = "--strict-markers"
 
diff --git a/tests/functional/conftest.py b/tests/functional/conftest.py
index 750723a..895fab9 100644
--- a/tests/functional/conftest.py
+++ b/tests/functional/conftest.py
@@ -79,23 +79,25 @@ async def credential_helper() -> CredentialHelper:
     _ = load_dotenv()
     client_id = os.environ["OAUTH_CLIENT_ID"]
     client_secret = os.environ["OAUTH_CLIENT_SECRET"]
-    auth_url = os.getenv(
-        "OAUTH_AUTH_URL", "https://crispthinking.auth0.com/oauth/token"
-    )
-    audience = os.getenv("OAUTH_AUDIENCE", "crisp-athena-live")
+    auth_url = os.getenv("OAUTH_AUTH_URL")
+    audience = os.getenv("OAUTH_AUDIENCE")
 
     # Create credential helper
-    return CredentialHelper(
-        client_id=client_id,
-        client_secret=client_secret,
-        auth_url=auth_url,
-        audience=audience,
-    )
+    kwargs: dict[str, str] = {
+        "client_id": client_id,
+        "client_secret": client_secret,
+    }
+    if auth_url:
+        kwargs["auth_url"] = auth_url
+    if audience:
+        kwargs["audience"] = audience
+
+    return CredentialHelper(proactive_refresh_threshold=0.25, **kwargs)
 
 
 def _load_options() -> AthenaOptions:
     _ = load_dotenv()
-    host = os.getenv("ATHENA_HOST", "localhost")
+    host = os.getenv("ATHENA_HOST")
 
     deployment_id = f"functional-test-{uuid.uuid4()}"
     if len(deployment_id) > MAX_DEPLOYMENT_ID_LENGTH:
@@ -104,8 +106,7 @@ def _load_options() -> AthenaOptions:
     affiliate = os.environ["ATHENA_TEST_AFFILIATE"]
 
     # Run classification with OAuth authentication
-    return AthenaOptions(
-        host=host,
+    opts = AthenaOptions(
         resize_images=True,
         deployment_id=deployment_id,
         compress_images=True,
@@ -115,6 +116,11 @@ def _load_options() -> AthenaOptions:
         compression_quality=2,
     )
 
+    if host:
+        opts.host = host
+
+    return opts
+
 
 @pytest.fixture
 def athena_options() -> AthenaOptions:
diff --git a/tests/functional/test_classify_single_soak.py b/tests/functional/test_classify_single_soak.py
new file mode 100644
index 0000000..5cdcfe2
--- /dev/null
+++ b/tests/functional/test_classify_single_soak.py
@@ -0,0 +1,66 @@
+import grpc
+import pytest
+
+from common_utils.image_generation import create_test_image
+from resolver_athena_client.client.athena_client import AthenaClient
+from resolver_athena_client.client.athena_options import AthenaOptions
+from resolver_athena_client.client.channel import (
+    CredentialHelper,
+    create_channel_with_credentials,
+)
+from resolver_athena_client.client.models import ImageData
+
+SOAK_ITERATIONS = 1000
+MIN_HASH_CHECK_SUCCESS_RATE = 0.95
+
+
+@pytest.mark.asyncio
+@pytest.mark.functional
+@pytest.mark.soak
+async def test_classify_single_hash_check_soak(
+    athena_options: AthenaOptions, credential_helper: CredentialHelper
+) -> None:
+    """Soak test: classify images and assert hash check result exists."""
+
+    channel = await create_channel_with_credentials(
+        athena_options.host, credential_helper
+    )
+
+    async with AthenaClient(channel, athena_options) as client:
+        successes = 0
+        failures: list[str] = []
+
+        for i in range(SOAK_ITERATIONS):
+            image_bytes = create_test_image()
+            image_data = ImageData(image_bytes)
+
+            try:
+                result = await client.classify_single(image_data)
+            except grpc.aio.AioRpcError as e:
+                failures.append(
+                    f"Iteration {i}: gRPC error {e.code()} - {e.details()}"
+                )
+                continue
+
+            if result.error.code:
+                failures.append(
+                    f"Iteration {i}: error {result.error.code}"
+                    f" - {result.error.message}"
+                )
+                continue
+
+            found_hash_check = any(
+                c.label.startswith("KnownCSAM-") for c in result.classifications
+            )
+            if found_hash_check:
+                successes += 1
+            else:
+                failures.append(
+                    f"Iteration {i}: no KnownCSAM- classification found"
+                )
+
+        success_rate = successes / SOAK_ITERATIONS
+        assert success_rate >= MIN_HASH_CHECK_SUCCESS_RATE, (
+            f"Hash check success rate {success_rate:.1%} is below 95%. "
+            f"{len(failures)} failures:\n" + "\n".join(failures[:20])
+        )