diff --git a/docs/openapi.json b/docs/openapi.json
index 82ada88a9..f5695f94a 100644
--- a/docs/openapi.json
+++ b/docs/openapi.json
@@ -355,7 +355,7 @@
                             }
                         ]
                     },
-                    "400": {
+                    "401": {
                         "description": "Missing or invalid credentials provided by client",
                         "content": {
                             "application/json": {
@@ -375,6 +375,9 @@
                             }
                         }
                     },
+                    "404": {
+                        "description": "Requested model or provider not found"
+                    },
                     "429": {
                         "description": "The quota has been exceeded",
                         "content": {
diff --git a/src/app/endpoints/query.py b/src/app/endpoints/query.py
index 4993da1a6..2fbef609e 100644
--- a/src/app/endpoints/query.py
+++ b/src/app/endpoints/query.py
@@ -80,7 +80,7 @@
             }
         ],
     },
-    400: {
+    401: {
         "description": "Missing or invalid credentials provided by client",
         "model": UnauthorizedResponse,
     },
@@ -88,6 +88,9 @@
         "description": "Client does not have permission to access conversation",
         "model": ForbiddenResponse,
     },
+    404: {
+        "description": "Requested model or provider not found",
+    },
     429: {
         "description": "The quota has been exceeded",
         "model": QuotaExceededResponse,
@@ -486,6 +489,17 @@ def select_model_and_provider_id(
     Raises:
         HTTPException: If no suitable LLM model is found or the selected model is not available.
     """
+    # If no models are available, raise an exception
+    if not models:
+        message = "No models available"
+        logger.error(message)
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail={
+                "response": constants.UNABLE_TO_PROCESS_RESPONSE,
+                "cause": message,
+            },
+        )
     # If model_id and provider_id are provided in the request, use them
 
     # If model_id is not provided in the request, check the configuration
@@ -516,10 +530,10 @@ def select_model_and_provider_id(
             model_label = model_id.split("/", 1)[1] if "/" in model_id else model_id
             return model_id, model_label, provider_id
         except (StopIteration, AttributeError) as e:
-            message = "No LLM model found in available models"
+            message = "No models available"
             logger.error(message)
             raise HTTPException(
-                status_code=status.HTTP_400_BAD_REQUEST,
+                status_code=status.HTTP_404_NOT_FOUND,
                 detail={
                     "response": constants.UNABLE_TO_PROCESS_RESPONSE,
                     "cause": message,
@@ -536,7 +550,7 @@ def select_model_and_provider_id(
         message = f"Model {model_id} from provider {provider_id} not found in available models"
         logger.error(message)
         raise HTTPException(
-            status_code=status.HTTP_400_BAD_REQUEST,
+            status_code=status.HTTP_404_NOT_FOUND,
             detail={
                 "response": constants.UNABLE_TO_PROCESS_RESPONSE,
                 "cause": message,
diff --git a/src/authentication/jwk_token.py b/src/authentication/jwk_token.py
index e10bf81a9..f9365f0c7 100644
--- a/src/authentication/jwk_token.py
+++ b/src/authentication/jwk_token.py
@@ -142,12 +142,12 @@ async def __call__(self, request: Request) -> AuthTuple:
             ) from exc
         except DecodeError as exc:
             raise HTTPException(
-                status_code=status.HTTP_400_BAD_REQUEST,
+                status_code=status.HTTP_401_UNAUTHORIZED,
                 detail="Invalid token: decode error",
             ) from exc
         except JoseError as exc:
             raise HTTPException(
-                status_code=status.HTTP_400_BAD_REQUEST,
+                status_code=status.HTTP_401_UNAUTHORIZED,
                 detail="Invalid token: unknown error",
             ) from exc
         except Exception as exc:
diff --git a/src/authentication/utils.py b/src/authentication/utils.py
index c92898ac2..57ba51288 100644
--- a/src/authentication/utils.py
+++ b/src/authentication/utils.py
@@ -15,12 +15,12 @@ def extract_user_token(headers: Headers) -> str:
     """
     authorization_header = headers.get("Authorization")
     if not authorization_header:
-        raise HTTPException(status_code=400, detail="No Authorization header found")
+        raise HTTPException(status_code=401, detail="No Authorization header found")
 
     scheme_and_token = authorization_header.strip().split()
     if len(scheme_and_token) != 2 or scheme_and_token[0].lower() != "bearer":
         raise HTTPException(
-            status_code=400, detail="No token found in Authorization header"
+            status_code=401, detail="No token found in Authorization header"
         )
 
     return scheme_and_token[1]
diff --git a/tests/e2e/config/no-models-run.yaml b/tests/e2e/config/no-models-run.yaml
new file mode 100644
index 000000000..d5686c832
--- /dev/null
+++ b/tests/e2e/config/no-models-run.yaml
@@ -0,0 +1,30 @@
+---
+# A run configuration for lightspeed-stack that defines no models.
+# Used for E2E testing.
+llm:
+  mode: "library"
+  model_name: ""
+  model_provider: ""
+  api_key: "EMPTY"
+  parameters:
+    max_new_tokens: 256
+  server:
+    host: "0.0.0.0"
+    port: 8080
+    url: "http://llama-stack:8080"
+lightspeed_stack:
+  server:
+    host: "0.0.0.0"
+    port: 8008
+  logging:
+    level: "INFO"
+    style: "default"
+  model_defaults:
+    provider: "openai"
+    model: "gpt-4-turbo"
+  providers:
+    - name: "openai"
+      api_key: "EMPTY"
+      url: "http://llama-stack:8080"
+      type: "openai"
+      models: []
diff --git a/tests/e2e/features/authorized_noop_token.feature b/tests/e2e/features/authorized_noop_token.feature
index 1169c6090..8c67d4732 100644
--- a/tests/e2e/features/authorized_noop_token.feature
+++ b/tests/e2e/features/authorized_noop_token.feature
@@ -11,7 +11,7 @@ Feature: Authorized endpoint API tests for the noop-with-token authentication mo
      """
      {"placeholder":"abc"}
      """
-     Then The status code of the response is 400
+     Then The status code of the response is 401
       And The body of the response is the following
           """
             {"detail": "No Authorization header found"}
diff --git a/tests/e2e/features/conversations.feature b/tests/e2e/features/conversations.feature
index dfbea8fe8..9619961c5 100644
--- a/tests/e2e/features/conversations.feature
+++ b/tests/e2e/features/conversations.feature
@@ -34,7 +34,7 @@ Feature: conversations endpoint API tests
     And I store conversation details
     And I remove the auth header
      When I access REST API endpoint "conversations" using HTTP GET method
-     Then The status code of the response is 400
+     Then The status code of the response is 401
      And The body of the response is the following
         """
         {
@@ -100,7 +100,7 @@ Feature: conversations endpoint API tests
     And I store conversation details
     And I remove the auth header
      When I use REST API conversation endpoint with conversation_id from above using HTTP GET method
-     Then The status code of the response is 400
+     Then The status code of the response is 401
      And The body of the response is the following
       """
       {
diff --git a/tests/e2e/features/environment.py b/tests/e2e/features/environment.py
index 45f22cbb8..2a0c5f0de 100644
--- a/tests/e2e/features/environment.py
+++ b/tests/e2e/features/environment.py
@@ -78,6 +78,8 @@ def before_scenario(context: Context, scenario: Scenario) -> None:
         context.scenario_config = (
             "tests/e2e/configuration/lightspeed-stack-invalid-feedback-storage.yaml"
         )
+    if "no_models" in scenario.effective_tags:
+        context.scenario_config = "tests/e2e/config/no-models-run.yaml"
 
 
 def after_scenario(context: Context, scenario: Scenario) -> None:
diff --git a/tests/e2e/features/feedback.feature b/tests/e2e/features/feedback.feature
index 18a997147..060beab9b 100644
--- a/tests/e2e/features/feedback.feature
+++ b/tests/e2e/features/feedback.feature
@@ -108,7 +108,7 @@ Feature: feedback endpoint API tests
      And The body of the response is the following
         """
         {
-            "detail": "Forbidden: User is not authorized to access this resource"
+            "detail": "Forbidden: Feedback is disabled"
         }   
         """
 
@@ -246,7 +246,6 @@ Feature: feedback endpoint API tests
   Scenario: Check if feedback endpoint is not working when not authorized
     Given The system is in default state
     And A new conversation is initialized
-    And I remove the auth header
      When I submit the following feedback for the conversation created before
         """
         {
@@ -256,14 +255,11 @@ Feature: feedback endpoint API tests
             "user_question": "Sample Question"
         }
         """
-     Then The status code of the response is 400
+     Then The status code of the response is 401
      And The body of the response is the following
         """
         {
-            "detail": {
-                        "cause": "Missing or invalid credentials provided by client",
-                        "response": "Unauthorized"
-            }
+            "detail": "No Authorization header found"
         }
         """
 
@@ -271,14 +267,11 @@ Feature: feedback endpoint API tests
     Given The system is in default state
     And I remove the auth header
      When The feedback is enabled
-     Then The status code of the response is 400
+     Then The status code of the response is 401
      And The body of the response is the following
         """
         {
-            "detail": {
-                        "cause": "Missing or invalid credentials provided by client",
-                        "response": "Unauthorized"
-            }
+            "detail": "No Authorization header found"
         }
         """
 
diff --git a/tests/e2e/features/query.feature b/tests/e2e/features/query.feature
index 585546fb2..e4b5ddf81 100644
--- a/tests/e2e/features/query.feature
+++ b/tests/e2e/features/query.feature
@@ -53,12 +53,36 @@ Feature: Query endpoint API tests
      """
      {"query": "Write a simple code for reversing string"}
      """
-      Then The status code of the response is 400
+      Then The status code of the response is 401
       And The body of the response is the following
           """
           {"detail": "No Authorization header found"}
           """
 
+  Scenario: Check if LLM responds to sent question with error when authenticated with invalid token
+    Given The system is in default state
+    And I set the Authorization header to Bearer invalid
+    When I use "query" to ask question with authorization header
+     """
+     {"query": "Write a simple code for reversing string"}
+     """
+      Then The status code of the response is 401
+      And The body of the response is the following
+          """
+          {"detail":"Invalid token: decode error"}
+          """
+
+  Scenario: Check if LLM responds to sent question with error when model does not exist
+    Given The system is in default state
+    And I set the Authorization header to Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6Ikpva
+    When I use "query" to ask question with authorization header
+     """
+     {"query": "Write a simple code for reversing string", "model": "does-not-exist", "provider": "does-not-exist"}
+     """
+      Then The status code of the response is 404
+      And The body of the response contains Model does-not-exist from provider does-not-exist not found in available models
+
+
   Scenario: Check if LLM responds to sent question with error when attempting to access conversation
     Given The system is in default state
      And I set the Authorization header to Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6Ikpva
@@ -138,3 +162,4 @@ Scenario: Check if LLM responds for query request with error for missing query
     }
     """
     Then The status code of the response is 200
+
diff --git a/tests/e2e/features/streaming_query.feature b/tests/e2e/features/streaming_query.feature
index 27196ccb7..0f74e1739 100644
--- a/tests/e2e/features/streaming_query.feature
+++ b/tests/e2e/features/streaming_query.feature
@@ -126,7 +126,7 @@ Feature: streaming_query endpoint API tests
      """
      {"query": "Say hello"}
      """
-      Then The status code of the response is 400
+      Then The status code of the response is 401
       And The body of the response is the following
           """
           {"detail": "No Authorization header found"}
diff --git a/tests/integration/test_openapi_json.py b/tests/integration/test_openapi_json.py
index 8fe1c689f..adf616e04 100644
--- a/tests/integration/test_openapi_json.py
+++ b/tests/integration/test_openapi_json.py
@@ -129,7 +129,7 @@ def test_servers_section_present_from_url(spec_from_url: dict[str, Any]) -> None
         ("/v1/shields", "get", {"200", "500"}),
         ("/v1/providers", "get", {"200", "500"}),
         ("/v1/providers/{provider_id}", "get", {"200", "404", "422", "500"}),
-        ("/v1/query", "post", {"200", "400", "403", "500", "422"}),
+        ("/v1/query", "post", {"200", "401", "403", "404", "500", "422"}),
         ("/v1/streaming_query", "post", {"200", "400", "401", "403", "422", "500"}),
         ("/v1/config", "get", {"200", "503"}),
         ("/v1/feedback", "post", {"200", "401", "403", "500", "422"}),
@@ -185,7 +185,7 @@ def test_paths_and_responses_exist_from_file(
         ("/v1/shields", "get", {"200", "500"}),
         ("/v1/providers", "get", {"200", "500"}),
         ("/v1/providers/{provider_id}", "get", {"200", "404", "422", "500"}),
-        ("/v1/query", "post", {"200", "400", "403", "500", "422"}),
+        ("/v1/query", "post", {"200", "401", "403", "404", "500", "422"}),
         ("/v1/streaming_query", "post", {"200", "400", "401", "403", "422", "500"}),
         ("/v1/config", "get", {"200", "503"}),
         ("/v1/feedback", "post", {"200", "401", "403", "500", "422"}),
diff --git a/tests/unit/app/endpoints/test_authorized.py b/tests/unit/app/endpoints/test_authorized.py
index ab92cb32c..d67c168b9 100644
--- a/tests/unit/app/endpoints/test_authorized.py
+++ b/tests/unit/app/endpoints/test_authorized.py
@@ -55,12 +55,12 @@ async def test_authorized_dependency_unauthorized() -> None:
     headers_no_auth = Headers({})
     with pytest.raises(HTTPException) as exc_info:
         extract_user_token(headers_no_auth)
-    assert exc_info.value.status_code == 400
+    assert exc_info.value.status_code == 401
     assert exc_info.value.detail == "No Authorization header found"
 
     # Test case 2: Invalid Authorization header format (400 error from extract_user_token)
     headers_invalid_auth = Headers({"Authorization": "InvalidFormat"})
     with pytest.raises(HTTPException) as exc_info:
         extract_user_token(headers_invalid_auth)
-    assert exc_info.value.status_code == 400
+    assert exc_info.value.status_code == 401
     assert exc_info.value.detail == "No token found in Authorization header"
diff --git a/tests/unit/app/endpoints/test_query.py b/tests/unit/app/endpoints/test_query.py
index 9b10d970e..2b215fa0d 100644
--- a/tests/unit/app/endpoints/test_query.py
+++ b/tests/unit/app/endpoints/test_query.py
@@ -459,7 +459,7 @@ def test_select_model_and_provider_id_no_available_models(
             mock_client.models.list(), query_request.model, query_request.provider
         )
 
-    assert "No LLM model found in available models" in str(exc_info.value)
+    assert "No models available" in str(exc_info.value)
 
 
 def test_validate_attachments_metadata() -> None:
diff --git a/tests/unit/authentication/test_jwk_token.py b/tests/unit/authentication/test_jwk_token.py
index 4a08294fe..613c821e6 100644
--- a/tests/unit/authentication/test_jwk_token.py
+++ b/tests/unit/authentication/test_jwk_token.py
@@ -302,7 +302,7 @@ async def test_no_bearer(
     with pytest.raises(HTTPException) as exc_info:
         await dependency(not_bearer_token_request)
 
-    assert exc_info.value.status_code == 400
+    assert exc_info.value.status_code == 401
     assert exc_info.value.detail == "No token found in Authorization header"
 
 
diff --git a/tests/unit/authentication/test_noop_with_token.py b/tests/unit/authentication/test_noop_with_token.py
index b18ae7a16..8fcd684b8 100644
--- a/tests/unit/authentication/test_noop_with_token.py
+++ b/tests/unit/authentication/test_noop_with_token.py
@@ -81,7 +81,7 @@ async def test_noop_with_token_auth_dependency_no_token() -> None:
     with pytest.raises(HTTPException) as exc_info:
         await dependency(request)
 
-    assert exc_info.value.status_code == 400
+    assert exc_info.value.status_code == 401
     assert exc_info.value.detail == "No Authorization header found"
 
 
@@ -102,5 +102,5 @@ async def test_noop_with_token_auth_dependency_no_bearer() -> None:
     with pytest.raises(HTTPException) as exc_info:
         await dependency(request)
 
-    assert exc_info.value.status_code == 400
+    assert exc_info.value.status_code == 401
     assert exc_info.value.detail == "No token found in Authorization header"
diff --git a/tests/unit/authentication/test_utils.py b/tests/unit/authentication/test_utils.py
index ee1d34dc8..5b1949ffd 100644
--- a/tests/unit/authentication/test_utils.py
+++ b/tests/unit/authentication/test_utils.py
@@ -19,7 +19,7 @@ def test_extract_user_token_no_header() -> None:
     try:
         extract_user_token(headers)
     except HTTPException as exc:
-        assert exc.status_code == 400
+        assert exc.status_code == 401
         assert exc.detail == "No Authorization header found"
 
 
@@ -29,5 +29,5 @@ def test_extract_user_token_invalid_format() -> None:
     try:
         extract_user_token(headers)
     except HTTPException as exc:
-        assert exc.status_code == 400
+        assert exc.status_code == 401
         assert exc.detail == "No token found in Authorization header"