diff --git a/litellm/anthropic_interface/exceptions/exception_mapping_utils.py b/litellm/anthropic_interface/exceptions/exception_mapping_utils.py
index d8198e41239..af58b14ac57 100644
--- a/litellm/anthropic_interface/exceptions/exception_mapping_utils.py
+++ b/litellm/anthropic_interface/exceptions/exception_mapping_utils.py
@@ -23,6 +23,7 @@ ANTHROPIC_ERROR_TYPE_MAP: Final[dict[int, AnthropicErrorType]] = {
     403: "permission_error",
     404: "not_found_error",
     413: "request_too_large",
+    422: "invalid_request_error",
     429: "rate_limit_error",
     500: "api_error",
     529: "overloaded_error",
diff --git a/litellm/proxy/anthropic_endpoints/endpoints.py b/litellm/proxy/anthropic_endpoints/endpoints.py
index 3d2f89be15f..eacc7815cab 100644
--- a/litellm/proxy/anthropic_endpoints/endpoints.py
+++ b/litellm/proxy/anthropic_endpoints/endpoints.py
@@ -13,8 +13,6 @@ from typing_extensions import ReadOnly, TypedDict
 
 import litellm
 from litellm.anthropic_interface.exceptions import (
-    AnthropicErrorDetail,
-    AnthropicErrorResponse,
     AnthropicExceptionMapping,
 )
 from litellm.integrations.custom_guardrail import ModifyResponseException
@@ -36,13 +34,14 @@ from litellm.proxy.common_request_processing import (
     resolve_counted_tool_fields,
     resolve_litellm_call_id,
 )
-from litellm.proxy.common_utils.error_body_call_id import error_body_call_id
+from litellm.proxy.common_utils.anthropic_error_payload import (
+    anthropic_error_json_response,
+)
 from litellm.proxy.common_utils.http_parsing_utils import (  # noqa: F401  # legacy module exports
     _read_request_body,  # pyright: ignore[reportPrivateUsage,reportUnusedImport]  # backwards-compatible package export
     read_request_body,
 )
 from litellm.proxy.common_utils.openai_error_payload import (
-    LITELLM_CALL_ID_HEADER,
     error_status_code,
     openai_error_param,
     openai_error_type,
@@ -55,44 +54,13 @@ from litellm.router import Router
 router: Final = APIRouter()
 
 
-def _with_provider_specific_fields(exc: ProxyException, detail: AnthropicErrorDetail) -> AnthropicErrorDetail:
-    if not exc.provider_specific_fields:
-        return detail
-    with_fields: Final[AnthropicErrorDetail] = {**detail, "provider_specific_fields": exc.provider_specific_fields}
-    return with_fields
-
-
-def _anthropic_error_detail(
-    exc: ProxyException, detail: AnthropicErrorDetail, call_id: str | None
-) -> AnthropicErrorDetail:
-    if call_id is None:
-        return _with_provider_specific_fields(exc, detail)
-    with_call_id: Final[AnthropicErrorDetail] = {
-        **_with_provider_specific_fields(exc, detail),
-        "litellm_call_id": call_id,
-    }
-    return with_call_id
-
-
 def _anthropic_error_json_response(exc: ProxyException, request: Request) -> JSONResponse:
-    from litellm.proxy.proxy_server import (
-        _close_dangling_otel_server_span,  # pyright: ignore[reportPrivateUsage]  # proxy_server keeps the span-close helper private; error JSONResponses returned by the route must stamp the OTel server span like the global ProxyException handler does
-        general_settings_view,
-    )
+    """The Anthropic error envelope for a failure raised inside a Messages handler.
 
-    status_code: Final = int(exc.code) if exc.code is not None and exc.code.isdigit() else 500
-    _close_dangling_otel_server_span(request, status_code, exc=exc)
-    envelope: Final = AnthropicExceptionMapping.transform_to_anthropic_error(
-        status_code=status_code,
-        raw_message=exc.message,
-        request_id=request.headers.get("x-request-id"),
-    )
-    body_call_id: Final = error_body_call_id(general_settings_view(), exc.headers.get(LITELLM_CALL_ID_HEADER))
-    content: Final[AnthropicErrorResponse] = {
-        **envelope,
-        "error": _anthropic_error_detail(exc, envelope["error"], body_call_id),
-    }
-    return JSONResponse(status_code=status_code, content=content, headers=exc.headers)
+    Delegates to the shared renderer so a failure raised here and one raised by the auth
+    layer before the handler (see the central ProxyException handler) answer identically.
+    """
+    return anthropic_error_json_response(exc, request)
 
 
 _TOKEN_COUNT_FIELDS: Final = ("model", "messages", "tools", "system")
diff --git a/litellm/proxy/common_utils/anthropic_error_payload.py b/litellm/proxy/common_utils/anthropic_error_payload.py
new file mode 100644
index 00000000000..d303e96427d
--- /dev/null
+++ b/litellm/proxy/common_utils/anthropic_error_payload.py
@@ -0,0 +1,110 @@
+"""Renders the Anthropic error envelope for the Messages routes, wherever the failure is raised.
+
+The central ``ProxyException`` handler answers every route with OpenAI's ``{"error": {...}}``
+body, which an Anthropic SDK cannot read. Auth, key, budget and model-access failures are
+raised by ``user_api_key_auth`` before the Messages handler runs, so the envelope is picked
+from the request route rather than inside the handler.
+"""
+
+from collections.abc import Mapping
+from typing import Final
+
+from fastapi import Request, status
+from fastapi.responses import JSONResponse
+
+from litellm.anthropic_interface.exceptions import (
+    AnthropicErrorDetail,
+    AnthropicErrorResponse,
+    AnthropicExceptionMapping,
+)
+from litellm.proxy._types import ProxyException
+from litellm.proxy.common_utils.error_body_call_id import error_body_call_id
+from litellm.proxy.common_utils.openai_error_payload import LITELLM_CALL_ID_HEADER
+
+ANTHROPIC_MESSAGES_ROUTES: Final[frozenset[str]] = frozenset(
+    {
+        "/v1/messages",
+        "/v1/messages/count_tokens",
+        "/claude_code_gateway/v1/messages",
+        "/claude_code_gateway/v1/messages/count_tokens",
+    }
+)
+
+
+def is_anthropic_messages_route(route: str) -> bool:
+    """True for the Messages routes, whose callers read the Anthropic error envelope.
+
+    Narrower than ``LiteLLMRoutes.anthropic_routes``: the Skills and marketplace routes there
+    answer their own body shape, and ``/anthropic/v1/messages`` relays the upstream response.
+    """
+    return route in ANTHROPIC_MESSAGES_ROUTES
+
+
+def anthropic_error_status_code(exc: ProxyException) -> int:
+    """The exception's stringified ``code`` as a status, else 500.
+
+    ``ProxyException.__init__`` stringifies ``code``, so a code-less exception holds the
+    literal ``"None"``, which must not be parsed as a status.
+    """
+    code: Final = exc.code
+    if code.isdigit():
+        return int(code)
+    return status.HTTP_500_INTERNAL_SERVER_ERROR
+
+
+def _with_provider_specific_fields(exc: ProxyException, detail: AnthropicErrorDetail) -> AnthropicErrorDetail:
+    if not exc.provider_specific_fields:
+        return detail
+    with_fields: Final[AnthropicErrorDetail] = {**detail, "provider_specific_fields": exc.provider_specific_fields}
+    return with_fields
+
+
+def _anthropic_error_detail(
+    exc: ProxyException, detail: AnthropicErrorDetail, call_id: str | None
+) -> AnthropicErrorDetail:
+    if call_id is None:
+        return _with_provider_specific_fields(exc, detail)
+    with_call_id: Final[AnthropicErrorDetail] = {
+        **_with_provider_specific_fields(exc, detail),
+        "litellm_call_id": call_id,
+    }
+    return with_call_id
+
+
+def anthropic_error_content(
+    exc: ProxyException,
+    status_code: int,
+    request_id: str | None,
+    general_settings: Mapping[str, object],
+) -> AnthropicErrorResponse:
+    """The Anthropic ``{"type": "error", "error": {...}}`` body for ``exc``, typed by status."""
+    envelope: Final = AnthropicExceptionMapping.transform_to_anthropic_error(
+        status_code=status_code,
+        raw_message=exc.message,
+        request_id=request_id,
+    )
+    body_call_id: Final = error_body_call_id(general_settings, exc.headers.get(LITELLM_CALL_ID_HEADER))
+    content: Final[AnthropicErrorResponse] = {
+        **envelope,
+        "error": _anthropic_error_detail(exc, envelope["error"], body_call_id),
+    }
+    return content
+
+
+def anthropic_error_json_response(exc: ProxyException, request: Request) -> JSONResponse:
+    """The Anthropic error response for a Messages request, span close included.
+
+    Shared by the Messages handlers and the central handler, so a failure raised before the
+    handler and one raised inside it answer identically.
+    """
+    from litellm.proxy.proxy_server import (
+        _close_dangling_otel_server_span,  # pyright: ignore[reportPrivateUsage]  # proxy_server keeps the span-close helper private; a JSONResponse returned instead of a raised error must stamp the OTel server span like the global ProxyException handler does
+        general_settings_view,
+    )
+
+    status_code: Final = anthropic_error_status_code(exc)
+    _close_dangling_otel_server_span(request, status_code, exc=exc)
+    content: Final = anthropic_error_content(
+        exc, status_code, request.headers.get("x-request-id"), general_settings_view()
+    )
+    return JSONResponse(status_code=status_code, content=content, headers=exc.headers)
diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index bc79becf7bb..0b60d969265 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -402,6 +402,7 @@ from litellm.proxy.auth.auth_object_prefetch import AUTH_OBJECTS_TARGET
 from litellm.proxy.auth.auth_utils import (
     MAX_REQUEST_SIZE_MB_SETTING,
     check_response_size_is_safe,
+    get_request_route,
     is_request_body_safe,
     log_model_access_denial,
     log_once_if_budget_reservation_disabled,
@@ -465,6 +466,10 @@ from litellm.proxy.common_request_processing import (  # noqa: F401, RUF100  # l
     sse_error_payload,
     ttft_keepalive_interval,
 )
+from litellm.proxy.common_utils.anthropic_error_payload import (
+    anthropic_error_json_response,
+    is_anthropic_messages_route,
+)
 from litellm.proxy.common_utils.auth_cache_invalidation_pubsub import (
     AuthCacheInvalidationSubscriber,
 )
@@ -2184,6 +2189,8 @@ async def openai_exception_handler(request: Request, exc: ProxyException):
     # NOTE: DO NOT MODIFY THIS, its crucial to map to Openai exceptions
     log_model_access_denial(exc)
     headers: Final = exc.headers
+    if is_anthropic_messages_route(get_request_route(request)):
+        return anthropic_error_json_response(exc, request)
     error_dict: Final = with_call_id(
         JSON_OBJECT.validate_python(exc.to_dict()),
         error_body_call_id(general_settings_view(), headers.get(LITELLM_CALL_ID_HEADER)),
diff --git a/tests/integration/authorization/_hidden_alias_budget.py b/tests/integration/authorization/_hidden_alias_budget.py
index bee2a585cff..5b4bec18b94 100644
--- a/tests/integration/authorization/_hidden_alias_budget.py
+++ b/tests/integration/authorization/_hidden_alias_budget.py
@@ -150,6 +150,13 @@ def error_type(response: httpx.Response) -> str:
     return str(object_value(JSON_OBJECT.validate_json(response.content)["error"])["type"])
 
 
+def budget_refusal_error_type(route: str) -> str:
+    """The ``error.type`` a budget refusal carries on a route label from ``ROUTES``: the
+    Anthropic envelope on Messages (its budget refusal is raised in
+    ``user_api_key_auth``), the OpenAI ``budget_exceeded`` type on the other routes."""
+    return "invalid_request_error" if route == "messages" else "budget_exceeded"
+
+
 def settle(
     send: Callable[[str], httpx.Response], status: int, *, burst: int = GATEWAY_BURST, seconds: float = 60
 ) -> None:
diff --git a/tests/integration/authorization/test_alias_chain_budget_waiver.py b/tests/integration/authorization/test_alias_chain_budget_waiver.py
index 0908fa0691c..e9d922d14f9 100644
--- a/tests/integration/authorization/test_alias_chain_budget_waiver.py
+++ b/tests/integration/authorization/test_alias_chain_budget_waiver.py
@@ -44,6 +44,7 @@ from integration.authorization._hidden_alias_budget import (
     async_anthropic_client,
     async_openai_client,
     base_url,
+    budget_refusal_error_type,
     error_type,
     fresh_chat,
     fresh_message,
@@ -191,17 +192,18 @@ def _assert_refused(
     key: str,
     model: str,
     prefix: str,
+    route: str = "chat",
     send: Callable[[Gateway, str, str, str], httpx.Response] = fresh_chat,
 ) -> None:
     marker: Final = f"{prefix}-" + uuid.uuid4().hex
     refused: Final = send(candidate, model, key, marker)
-    assert _refusal(refused) == (BUDGET_EXCEEDED, "budget_exceeded"), refused.text
+    assert _refusal(refused) == (BUDGET_EXCEEDED, budget_refusal_error_type(route)), refused.text
     assert upstream_hits(upstream_requests(rig.gateway.upstream_url), marker) == 0
 
 
 def _assert_refused_on_every_route(rig: ChainRig, candidate: Gateway, key: str, model: str) -> None:
     for route, send in ROUTES:
-        _assert_refused(rig, candidate, key, model, f"refused-{route}", send)
+        _assert_refused(rig, candidate, key, model, f"refused-{route}", route, send)
 
 
 def _assert_provider_failure(response: httpx.Response) -> None:
diff --git a/tests/integration/authorization/test_claude_code_gateway_oauth.py b/tests/integration/authorization/test_claude_code_gateway_oauth.py
index a80eeacad46..700816c8d31 100644
--- a/tests/integration/authorization/test_claude_code_gateway_oauth.py
+++ b/tests/integration/authorization/test_claude_code_gateway_oauth.py
@@ -474,15 +474,14 @@ def test_device_authorization_polls_complete_sso_and_mints_a_model_restricted_be
             )
             assert model_b_response.status_code == 403, model_b_response.text
             assert _JSON_OBJECT.validate_json(model_b_response.content) == {
+                "type": "error",
                 "error": {
+                    "type": "permission_error",
                     "message": (
                         f"The requested model '{model_b}' is not available for this API key, or the model name is "
                         "invalid. Check the models available to you and try again."
                     ),
-                    "type": "team_model_access_denied",
-                    "param": "model",
-                    "code": "403",
-                }
+                },
             }, model_b_response.text
             assert upstream.drain() == ()
 
diff --git a/tests/integration/authorization/test_cli_sso_login_ui_disabled.py b/tests/integration/authorization/test_cli_sso_login_ui_disabled.py
index a53fbfacf4c..fd4c7246801 100644
--- a/tests/integration/authorization/test_cli_sso_login_ui_disabled.py
+++ b/tests/integration/authorization/test_cli_sso_login_ui_disabled.py
@@ -695,9 +695,11 @@ def test_cli_session_token_is_denied_once_its_team_budget_is_exhausted(
             key=key,
         )
         assert refused.status_code == 422, f"{refused.status_code} {refused.text}"
-        error: Final = object_value(JSON_OBJECT.validate_json(refused.content)["error"])
-        assert error["type"] == "budget_exceeded", refused.text
-        assert error["code"] == "422", refused.text
+        body: Final = JSON_OBJECT.validate_json(refused.content)
+        assert body["type"] == "error", refused.text
+        error: Final = object_value(body["error"])
+        assert error["type"] == "invalid_request_error", refused.text
+        assert "param" not in error and "code" not in error, refused.text
         message: Final = string_value(error["message"])
         assert "Budget has been exceeded!" in message, refused.text
         assert f"Team={team}" in message, refused.text
diff --git a/tests/integration/authorization/test_hidden_alias_budget_bypass.py b/tests/integration/authorization/test_hidden_alias_budget_bypass.py
index 51b36c145d3..e9e55a6aaf7 100644
--- a/tests/integration/authorization/test_hidden_alias_budget_bypass.py
+++ b/tests/integration/authorization/test_hidden_alias_budget_bypass.py
@@ -38,6 +38,7 @@ from integration.authorization._hidden_alias_budget import (
     async_anthropic_client,
     async_openai_client,
     base_url,
+    budget_refusal_error_type,
     chat_statuses,
     clear_provider_script,
     error_type,
@@ -599,7 +600,7 @@ def _assert_refused_like_target(rig: AliasRig, candidate: Gateway, key: str, sha
         target_marker: Final = f"target-{route}-" + uuid.uuid4().hex
         via_shadow: Final = send(candidate, shadow, key, shadow_marker)
         by_name: Final = send(candidate, target, key, target_marker)
-        assert _refusal(by_name) == (BUDGET_EXCEEDED, "budget_exceeded"), by_name.text
+        assert _refusal(by_name) == (BUDGET_EXCEEDED, budget_refusal_error_type(route)), by_name.text
         assert via_shadow.status_code == by_name.status_code, via_shadow.text
         assert error_type(via_shadow) == error_type(by_name), via_shadow.text
         observed: Final = upstream_requests(rig.gateway.upstream_url)
@@ -621,7 +622,7 @@ def _assert_refused_on_every_route(rig: AliasRig, candidate: Gateway, key: str,
         marker: Final = f"chain-{route}-" + uuid.uuid4().hex
         refused: Final = send(candidate, model, key, marker)
         assert refused.status_code == BUDGET_EXCEEDED, refused.text
-        assert error_type(refused) == "budget_exceeded", refused.text
+        assert error_type(refused) == budget_refusal_error_type(route), refused.text
         assert upstream_hits(upstream_requests(rig.gateway.upstream_url), marker) == 0
 
 
@@ -828,9 +829,9 @@ def _deployment_id(rig: AliasRig, name: str) -> str:
     return identities[0]
 
 
-def _assert_budget_refusal(status_code: int, body: str) -> None:
+def _assert_budget_refusal(status_code: int, body: str, route: str = "chat") -> None:
     assert status_code == BUDGET_EXCEEDED, body
-    assert "budget_exceeded" in body, body
+    assert budget_refusal_error_type(route) in body, body
 
 
 def _assert_no_served_row(key: str, marker: str) -> None:
@@ -881,7 +882,7 @@ async def test_exhausted_key_is_refused_on_shadowing_alias_through_streamed_anth
                     extra_headers=spend_marker(marker),
                 ) as stream:
                     await stream.get_final_message()
-        _assert_budget_refusal(refused.value.status_code, str(refused.value.body))
+        _assert_budget_refusal(refused.value.status_code, str(refused.value.body), route="messages")
         assert upstream_hits(upstream_requests(rig.gateway.upstream_url), marker) == 0
 
 
diff --git a/tests/integration/authorization/test_unknown_key_generic_401.py b/tests/integration/authorization/test_unknown_key_generic_401.py
index 8e6ff3fa3ab..7826c11bec8 100644
--- a/tests/integration/authorization/test_unknown_key_generic_401.py
+++ b/tests/integration/authorization/test_unknown_key_generic_401.py
@@ -50,7 +50,23 @@ class _ErrorResponse(BaseModel):
     error: _ProxyError
 
 
+class _AnthropicErrorDetail(BaseModel):
+    model_config = ConfigDict(frozen=True, extra="forbid")
+
+    type: str
+    message: str
+
+
+class _AnthropicErrorResponse(BaseModel):
+    model_config = ConfigDict(frozen=True)
+
+    type: str
+    error: _AnthropicErrorDetail
+
+
 GENERIC_ERROR: Final = _ProxyError(message=GENERIC_MESSAGE, type="token_not_found_in_db", param="key", code="401")
+MESSAGES_PATH: Final = "/v1/messages"
+ANTHROPIC_GENERIC_ERROR: Final = _AnthropicErrorDetail(type="authentication_error", message=GENERIC_MESSAGE)
 
 
 @dataclass(frozen=True, slots=True)
@@ -119,6 +135,23 @@ def _assert_generic_refusal(response: httpx.Response, *secrets: str) -> None:
         assert secret not in response.text, response.text
 
 
+def _assert_messages_refusal(response: httpx.Response, *secrets: str) -> None:
+    assert response.status_code == 401, response.text
+    body: Final = _AnthropicErrorResponse.model_validate_json(response.content)
+    assert body.type == "error", response.text
+    assert body.error == ANTHROPIC_GENERIC_ERROR, response.text
+    for secret in secrets:
+        assert secret not in response.text, response.text
+
+
+def _assert_refusal(path: str, response: httpx.Response, *secrets: str) -> None:
+    """The Messages routes answer the Anthropic envelope, every other route the OpenAI one."""
+    if path == MESSAGES_PATH:
+        _assert_messages_refusal(response, *secrets)
+    else:
+        _assert_generic_refusal(response, *secrets)
+
+
 def _side(gateway: Gateway, peer: Gateway, side: Side) -> Gateway:
     return gateway if side == "gateway" else peer
 
@@ -129,7 +162,10 @@ def test_an_unknown_key_gets_the_generic_401_without_reaching_the_provider(
     gateway: Gateway, peer: Gateway, provider: SharedProvider, route: str, side: Side
 ) -> None:
     key: Final = _unknown_key()
-    _assert_generic_refusal(_send(_side(gateway, peer, side), ROUTES[route], key), key, key[-4:], _digest(key))
+    request_route: Final = ROUTES[route]
+    _assert_refusal(
+        request_route.path, _send(_side(gateway, peer, side), request_route, key), key, key[-4:], _digest(key)
+    )
     assert provider.received() == ()
 
 
@@ -183,8 +219,9 @@ def test_two_different_unknown_keys_in_both_headers_get_the_generic_401_naming_n
     bearer: Final = _unknown_key()
     api_key: Final = _unknown_key()
     headers: Final = {**_headers("authorization", bearer), **_headers("x-api-key", api_key)}
-    for path, body in (("/v1/chat/completions", CHAT), ("/v1/messages", MESSAGES)):
-        _assert_generic_refusal(
+    for path, body in (("/v1/chat/completions", CHAT), (MESSAGES_PATH, MESSAGES)):
+        _assert_refusal(
+            path,
             gateway.client.post(path, json=dict(body), headers=headers),
             bearer,
             api_key,
@@ -359,16 +396,15 @@ async def _send_async(client: httpx.AsyncClient, route: _Route, key: str) -> htt
     )
 
 
-async def _burst(owned: OwnedProxy, keys: tuple[str, ...]) -> tuple[httpx.Response, ...]:
+async def _burst(owned: OwnedProxy, keys: tuple[str, ...]) -> tuple[tuple[_Route, httpx.Response], ...]:
+    """Each key's response paired with the route it was sent on, so the caller asserts the
+    envelope the route actually answered with."""
+    routes: Final = tuple(ROUTES[BURST_ROUTES[index % len(BURST_ROUTES)]] for index in range(len(keys)))
     async with httpx.AsyncClient(base_url=str(owned.gateway.client.base_url), timeout=60, trust_env=False) as client:
-        return tuple(
-            await asyncio.gather(
-                *(
-                    _send_async(client, ROUTES[BURST_ROUTES[index % len(BURST_ROUTES)]], key)
-                    for index, key in enumerate(keys)
-                )
-            )
+        responses: Final = await asyncio.gather(
+            *(_send_async(client, route, key) for route, key in zip(routes, keys, strict=True))
         )
+    return tuple(zip(routes, responses, strict=True))
 
 
 def _log_after(owned: OwnedProxy, offset: int) -> str:
@@ -397,7 +433,7 @@ async def test_a_burst_across_a_worker_kill_answers_every_unknown_key_with_the_g
             lambda text: all(_console_line(key) in text for key in keys),
             30,
         )
-    for response, key in zip((*during, *after), keys, strict=True):
-        _assert_generic_refusal(response, key, _digest(key))
+    for (route, response), key in zip((*during, *after), keys, strict=True):
+        _assert_refusal(route.path, response, key, _digest(key))
     assert [window.count(_console_line(key)) for key in keys] == [1] * len(keys)
     assert [key for key in keys if key in window] == []
diff --git a/tests/integration/messages_endpoint/providers/anthropic/test_anthropic_gateway_wire.py b/tests/integration/messages_endpoint/providers/anthropic/test_anthropic_gateway_wire.py
index e159573e9fd..0f0f1e7676c 100644
--- a/tests/integration/messages_endpoint/providers/anthropic/test_anthropic_gateway_wire.py
+++ b/tests/integration/messages_endpoint/providers/anthropic/test_anthropic_gateway_wire.py
@@ -268,15 +268,14 @@ def test_enabled_gateway_count_tokens_alias_matches_native_count_tokens_route(en
         )
         assert restricted_response.status_code == 403, restricted_response.text
         assert _JSON_OBJECT.validate_json(restricted_response.content) == {
+            "type": "error",
             "error": {
+                "type": "permission_error",
                 "message": (
                     f"The requested model '{restricted_model}' is not available for this API key, or the model name "
                     "is invalid. Check the models available to you and try again."
                 ),
-                "type": "key_model_access_denied",
-                "param": "model",
-                "code": "403",
-            }
+            },
         }, restricted_response.text
         assert wire.drain() == ()
 
@@ -285,15 +284,14 @@ def test_enabled_gateway_count_tokens_alias_matches_native_count_tokens_route(en
 def test_enabled_gateway_refuses_model_outside_virtual_key(enabled_gateway: Gateway) -> None:
     result: Final = _restricted_model_responses(enabled_gateway)
     expected_body: Final = {
+        "type": "error",
         "error": {
+            "type": "permission_error",
             "message": (
                 f"The requested model '{result[4]}' is not available for this API key, or the model name is invalid. "
                 "Check the models available to you and try again."
             ),
-            "type": "key_model_access_denied",
-            "param": "model",
-            "code": "403",
-        }
+        },
     }
     assert result[0] == result[2] == 403, (result[1], result[3])
     assert _JSON_OBJECT.validate_json(result[1]) == expected_body, result[1]
diff --git a/tests/integration/spend/test_end_user_budget_enforcement.py b/tests/integration/spend/test_end_user_budget_enforcement.py
index 02c8aee8f5e..92259d463b9 100644
--- a/tests/integration/spend/test_end_user_budget_enforcement.py
+++ b/tests/integration/spend/test_end_user_budget_enforcement.py
@@ -258,9 +258,20 @@ def _observed(upstream: httpx.Client) -> list[JsonValue]:
     return requests
 
 
-def _denial_error(denied: httpx.Response) -> dict[str, JsonValue]:
+def _denial_error(denied: httpx.Response, route: str) -> dict[str, JsonValue]:
     assert denied.status_code == 422, denied.text
-    return object_value(object_value(denied.json())["error"])
+    if route == "/v1/messages":
+        body: Final = object_value(denied.json())
+        assert body["type"] == "error", denied.text
+        anthropic_error: Final = object_value(body["error"])
+        assert anthropic_error["type"] == "invalid_request_error", denied.text
+        assert "param" not in anthropic_error and "code" not in anthropic_error, denied.text
+        return anthropic_error
+    openai_error: Final = object_value(object_value(denied.json())["error"])
+    assert openai_error["type"] == "budget_exceeded", denied.text
+    assert openai_error["param"] is None
+    assert openai_error["code"] == "422"
+    return openai_error
 
 
 def _prove_end_user_budget_lockout(
@@ -304,8 +315,7 @@ def _prove_end_user_budget_lockout(
     upstream.delete("/__observations").raise_for_status()
     denied: Final = _send(gateway, spelling, deployment, key, end_user_id, f"denied {end_user_id}")
     assert _observed(upstream) == [], denied.text
-    error: Final = _denial_error(denied)
-    assert error["type"] == "budget_exceeded", denied.text
+    error: Final = _denial_error(denied, spelling.route)
     matched: Final = re.fullmatch(
         rf"ExceededBudget: End User={re.escape(end_user_id)} over budget\. "
         rf"Spend=([-+]?(?:\d+(?:\.\d*)?|\.\d+)(?:[eE][-+]?\d+)?), Budget=0\.05",
diff --git a/tests/integration/spend/test_end_user_spend_without_proxy_user.py b/tests/integration/spend/test_end_user_spend_without_proxy_user.py
index 94884717092..3e455f9aa4f 100644
--- a/tests/integration/spend/test_end_user_spend_without_proxy_user.py
+++ b/tests/integration/spend/test_end_user_spend_without_proxy_user.py
@@ -120,6 +120,19 @@ def _assert_budget_refusal(response: httpx.Response, end_user: str) -> None:
     ]
 
 
+def _assert_messages_budget_refusal(response: httpx.Response, end_user: str) -> None:
+    """A budget refusal on /v1/messages keeps its 422 but answers the Anthropic envelope."""
+    assert response.status_code == 422, response.text
+    body: Final = _json_object(response.content)
+    assert body["type"] == "error", response.text
+    error: Final = object_value(body["error"])
+    assert error["type"] == "invalid_request_error"
+    assert "param" not in error and "code" not in error, response.text
+    assert str(error["message"]).startswith(f"ExceededBudget: End User={end_user} over budget. Spend="), error[
+        "message"
+    ]
+
+
 def _json_object(raw: bytes) -> dict[str, JsonValue]:
     return _JSON_OBJECT.validate_json(raw)
 
@@ -345,7 +358,7 @@ def test_anthropic_messages_metadata_user_id_is_charged_and_budget_enforced(gate
             json={**body, "messages": [{"role": "user", "content": f"again {uuid.uuid4().hex}"}]},
             headers={"x-api-key": key, "anthropic-version": "2023-06-01"},
         )
-        _assert_budget_refusal(denied, end_user)
+        _assert_messages_budget_refusal(denied, end_user)
         assert _observed(upstream) == []
 
 
diff --git a/tests/unit/anthropic_interface/exceptions/test_exception_mapping_utils.py b/tests/unit/anthropic_interface/exceptions/test_exception_mapping_utils.py
index 0d8e7674e7d..5c40bfafa08 100644
--- a/tests/unit/anthropic_interface/exceptions/test_exception_mapping_utils.py
+++ b/tests/unit/anthropic_interface/exceptions/test_exception_mapping_utils.py
@@ -63,10 +63,17 @@ class TestCreateErrorResponse:
         )
         assert response["request_id"] == "req_123"
 
-    def test_unknown_status_defaults_to_api_error(self):
-        """Test unknown status code defaults to api_error."""
-        response = AnthropicExceptionMapping.create_error_response(418, "I'm a teapot")
-        assert response["error"]["type"] == "api_error"
+    @pytest.mark.parametrize(
+        ("status_code", "expected_error_type"),
+        [(422, "invalid_request_error"), (418, "api_error"), (502, "api_error"), (599, "api_error")],
+    )
+    def test_a_budget_status_is_a_request_error_and_a_status_the_table_does_not_name_is_api_error(
+        self, status_code: int, expected_error_type: str
+    ):
+        """The proxy's budget status is a caller-fault request error, so the table names 422.
+        A status the table does not name, such as a 418 or a 5xx, keeps api_error."""
+        response = AnthropicExceptionMapping.create_error_response(status_code, "scripted status")
+        assert response["error"]["type"] == expected_error_type
 
 
 class TestExtractErrorMessage:
diff --git a/tests/unit/proxy/proxy_server/test_exception_handlers.py b/tests/unit/proxy/proxy_server/test_exception_handlers.py
index f6efdecc884..6b994e326ca 100644
--- a/tests/unit/proxy/proxy_server/test_exception_handlers.py
+++ b/tests/unit/proxy/proxy_server/test_exception_handlers.py
@@ -168,6 +168,159 @@ async def test_openai_exception_handler_never_fabricates_a_call_id(monkeypatch):
     assert "litellm_call_id" not in body["error"]
 
 
+# ---------------------------------------------------------------------------
+# openai_exception_handler: Anthropic envelope on the Messages routes
+# ---------------------------------------------------------------------------
+
+
+def _model_access_denied_exception():
+    """The 403 can_team_access_model raises: OpenAI type team_model_access_denied, param model."""
+    return ProxyException(
+        message="Team not allowed to access model. Tried to access gpt-5.6",
+        type="team_model_access_denied",
+        param="model",
+        code=403,
+    )
+
+
+_MESSAGES_ROUTES: Final = (
+    "/v1/messages",
+    "/v1/messages/count_tokens",
+    "/claude_code_gateway/v1/messages",
+    "/claude_code_gateway/v1/messages/count_tokens",
+)
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("path", _MESSAGES_ROUTES)
+async def test_openai_exception_handler_answers_the_anthropic_envelope_on_the_messages_routes(path):
+    """An auth failure raised before the Messages handler (user_api_key_auth) must reach an
+    Anthropic SDK as {"type": "error", "error": {...}}, not the OpenAI {"error": {...}} body."""
+    response = await openai_exception_handler(request=_make_request(path=path), exc=_model_access_denied_exception())
+    body = json.loads(response.body)
+
+    assert response.status_code == 403
+    assert body == {
+        "type": "error",
+        "error": {
+            "type": "permission_error",
+            "message": "Team not allowed to access model. Tried to access gpt-5.6",
+        },
+    }
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "status_code,anthropic_type",
+    [
+        (401, "authentication_error"),
+        (403, "permission_error"),
+        (404, "not_found_error"),
+        (429, "rate_limit_error"),
+    ],
+)
+async def test_openai_exception_handler_maps_messages_failures_to_anthropic_error_types(status_code, anthropic_type):
+    """The Anthropic error type follows the HTTP status, so a bad key, a denied model, an
+    unknown model and a rate limit each read the way an Anthropic client expects."""
+    exc = ProxyException(message="denied", type="key_model_access_denied", param="model", code=status_code)
+
+    response = await openai_exception_handler(request=_make_request(path="/v1/messages"), exc=exc)
+
+    assert response.status_code == status_code
+    assert json.loads(response.body)["error"]["type"] == anthropic_type
+
+
+@pytest.mark.asyncio
+async def test_openai_exception_handler_keeps_the_status_of_a_budget_failure_on_messages():
+    """A budget failure carries the proxy's own budget status; the Messages route must keep
+    it and answer the Anthropic envelope rather than the OpenAI body."""
+    exc = ProxyException(message="Budget exceeded", type="budget_exceeded", param=None, code=422)
+
+    response = await openai_exception_handler(request=_make_request(path="/v1/messages/count_tokens"), exc=exc)
+    body = json.loads(response.body)
+
+    assert response.status_code == 422
+    assert body["type"] == "error"
+    assert body["error"]["type"] == "invalid_request_error"
+    assert body["error"]["message"] == "Budget exceeded"
+    assert "param" not in body["error"] and "code" not in body["error"]
+
+
+@pytest.mark.asyncio
+async def test_openai_exception_handler_keeps_the_openai_envelope_off_the_messages_routes():
+    """The envelope is chosen by route, so OpenAI routes are untouched."""
+    response = await openai_exception_handler(
+        request=_make_request(path="/v1/chat/completions"), exc=_model_access_denied_exception()
+    )
+    body = json.loads(response.body)
+
+    assert response.status_code == 403
+    assert body == {
+        "error": {
+            "message": "Team not allowed to access model. Tried to access gpt-5.6",
+            "type": "team_model_access_denied",
+            "param": "model",
+            "code": "403",
+        }
+    }
+
+
+@pytest.mark.asyncio
+async def test_openai_exception_handler_keeps_the_openai_envelope_on_other_anthropic_routes():
+    """The Skills and marketplace routes are not Messages routes and answer their own body."""
+    response = await openai_exception_handler(
+        request=_make_request(path="/v1/skills"), exc=_model_access_denied_exception()
+    )
+    body = json.loads(response.body)
+
+    assert response.status_code == 403
+    assert "type" not in body
+    assert body["error"]["type"] == "team_model_access_denied"
+
+
+@pytest.mark.asyncio
+async def test_openai_exception_handler_messages_route_copies_the_call_id_when_opted_in(monkeypatch):
+    """The Messages envelope carries error.litellm_call_id under the same opt-in as the
+    OpenAI envelope, so an Anthropic SDK's e.body still names the request to look up."""
+    monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {"include_call_id_in_error_body": True})
+    exc = ProxyException(
+        message="denied",
+        type="team_model_access_denied",
+        param="model",
+        code=403,
+        headers={"x-litellm-call-id": "call-8302"},
+        provider_specific_fields={"guardrail": "keyword-block"},
+    )
+
+    response = await openai_exception_handler(request=_make_request(path="/v1/messages"), exc=exc)
+    body = json.loads(response.body)
+
+    assert response.headers["x-litellm-call-id"] == "call-8302"
+    assert body["error"] == {
+        "type": "permission_error",
+        "message": "denied",
+        "provider_specific_fields": {"guardrail": "keyword-block"},
+        "litellm_call_id": "call-8302",
+    }
+
+
+@pytest.mark.asyncio
+async def test_a_messages_request_with_no_key_answers_the_anthropic_authentication_error(client, monkeypatch):
+    """End to end through the real user_api_key_auth: a /v1/messages request with no
+    credential is rejected before the handler, and the SDK must see Anthropic's
+    authentication_error envelope, not OpenAI's {"error": {...}} body."""
+    monkeypatch.setattr("litellm.proxy.proxy_server.master_key", "test-master-key")
+    monkeypatch.setattr("litellm.proxy.proxy_server.general_settings", {})
+
+    response = client.post("/v1/messages", json={"model": "gpt-4", "messages": [{"role": "user", "content": "hi"}]})
+    body = response.json()
+
+    assert response.status_code == 401
+    assert body["type"] == "error"
+    assert body["error"]["type"] == "authentication_error"
+    assert "param" not in body["error"]
+
+
 # ---------------------------------------------------------------------------
 # _close_dangling_otel_server_span
 # ---------------------------------------------------------------------------