diff --git a/litellm/router.py b/litellm/router.py
index 20af2e5649e..f6f31e7bec3 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -5106,6 +5106,36 @@ class Router(DeprecatedRouterMembers):
         if "tool_choice" not in kwargs and dep_params.get("tool_choice") is not None:
             kwargs["tool_choice"] = dep_params["tool_choice"]
 
+    @staticmethod
+    def _apply_max_output_tokens_cap_to_request(
+        deployment: Mapping[str, object],
+        kwargs: dict[str, object],  # mutable-ok: the shared request mapping is updated in place
+    ) -> None:
+        """
+        Lower caller-requested completion token budgets to the deployment's
+        max_output_tokens_cap, when set (see litellm_params.max_output_tokens_cap).
+
+        Only lowers what the request already carries: a smaller caller budget is
+        respected, and requests without an output budget are untouched (a default
+        belongs in router default_litellm_params). Applies to the OpenAI token
+        budget fields so provider translation can normalize it afterwards.
+        """
+        dep_params_raw: Final[object] = deployment.get("litellm_params", {}) or {}
+        dep_params: Final = (
+            dep_params_raw
+            if isinstance(dep_params_raw, Mapping)
+            else dep_params_raw.model_dump(exclude_none=True)
+        )
+        cap: Final[object] = dep_params.get("max_output_tokens_cap")
+        if not isinstance(cap, int) or isinstance(cap, bool) or cap <= 0:
+            return
+        for name in ("max_tokens", "max_completion_tokens", "max_output_tokens"):
+            requested = kwargs.get(name)
+            if isinstance(requested, bool) or not isinstance(requested, int):
+                continue
+            if requested > cap:
+                kwargs[name] = cap  # rebind-ok: the clamped budget rides the shared request mapping to the provider call
+
     def _update_kwargs_with_deployment(
         self,
         deployment: dict,
@@ -5114,10 +5144,11 @@ class Router(DeprecatedRouterMembers):
         splits_stream_timeout: bool = False,
     ) -> None:
         """
-        5 jobs:
+        6 jobs:
         - Adds selected deployment, model_info and api_base to kwargs["metadata"] (used for logging)
         - Adds default litellm params to kwargs, if set.
         - Merges tools from deployment with request (proxy-configured tools + request tools).
+        - Lowers caller-requested completion token budgets to the deployment's max_output_tokens_cap, when set.
         - On a fallback hop, drops the encrypted reasoning this deployment cannot decrypt, keeping its summary.
         - On a Responses continuation, sends the partial response as prefill where this deployment takes one.
         """
@@ -5316,6 +5347,7 @@ class Router(DeprecatedRouterMembers):
         ):
             kwargs[STREAM_USAGE_INJECTED_FIELD] = True
         self._update_kwargs_with_default_litellm_params(kwargs=kwargs, metadata_variable_name=metadata_variable_name)
+        Router._apply_max_output_tokens_cap_to_request(deployment=deployment, kwargs=kwargs)
         hop_kwargs: Final = _FALLBACK_HOP_ADAPTER.validate_python(kwargs)
         if _is_fallback_hop(hop_kwargs):
             EncryptedContentAffinityCheck.strip_reasoning_the_targets_cannot_decrypt(
diff --git a/litellm/types/router.py b/litellm/types/router.py
index f927ae0475b..bcc79009b19 100644
--- a/litellm/types/router.py
+++ b/litellm/types/router.py
@@ -724,6 +724,7 @@ class LiteLLM_Params(GenericLiteLLMParams):
         def __init__(self, *, model: str, **data: object) -> None: ...  # kwargs-ok: provider fields vary by model
 
     model: str
+    max_output_tokens_cap: int | None = None
     model_config = ConfigDict(extra="allow", arbitrary_types_allowed=True)
 
     def __contains__(self, key) -> bool:
diff --git a/tests/unit/proxy/test_credential_slot_registry.py b/tests/unit/proxy/test_credential_slot_registry.py
index 6332038feb8..61d1f3b6c7d 100644
--- a/tests/unit/proxy/test_credential_slot_registry.py
+++ b/tests/unit/proxy/test_credential_slot_registry.py
@@ -128,6 +128,7 @@ DEPLOYMENT_PARAM_CLASSIFICATION: Final[Mapping[str, Classification]] = MappingPr
         "litellm_credential_name": NotSecret("name of a credentials table entry, not a credential"),
         "default_api_key_tpm_limit": NotSecret("rate limit number"),
         "default_api_key_rpm_limit": NotSecret("rate limit number"),
+        "max_output_tokens_cap": NotSecret("max completion-token budget, not a credential"),
         "valkey_password": Unplanted(),
         "anthropic_identity_token": Unplanted(),
         "anthropic_identity_token_file": Unplanted(),
@@ -156,6 +157,7 @@ REQUEST_BODY_PARAM_CLASSIFICATION: Final[Mapping[str, Classification]] = Mapping
         "litellm_credential_name": NotSecret("name of a credentials table entry, not a credential"),
         "default_api_key_tpm_limit": NotSecret("rate limit number"),
         "default_api_key_rpm_limit": NotSecret("rate limit number"),
+        "max_output_tokens_cap": NotSecret("max completion-token budget, not a credential"),
     }
 )
 
diff --git a/tests/unit/test_router/test_max_output_tokens_cap.py b/tests/unit/test_router/test_max_output_tokens_cap.py
new file mode 100644
index 00000000000..72650173d21
--- /dev/null
+++ b/tests/unit/test_router/test_max_output_tokens_cap.py
@@ -0,0 +1,128 @@
+"""
+Unit tests for per-deployment litellm_params.max_output_tokens_cap.
+
+The cap only lowers output-token budgets the caller already requested; smaller
+caller budgets win, and requests without any budget field are left alone (a
+default budget belongs in router default_litellm_params).
+"""
+
+import pytest
+
+from litellm import Router
+from litellm.types.router import LiteLLM_Params
+
+MODEL_LIST = [
+    {
+        "model_name": "capped-model",
+        "litellm_params": {
+            "model": "openai/capped-model",
+            "api_base": "http://localhost:9911/v1",
+            "api_key": "sk-not-real",
+            "max_output_tokens_cap": 500,
+        },
+    },
+    {
+        "model_name": "uncapped-model",
+        "litellm_params": {
+            "model": "openai/uncapped-model",
+            "api_base": "http://localhost:9911/v1",
+            "api_key": "sk-not-real",
+        },
+    },
+]
+
+BUDGET_FIELDS = ("max_tokens", "max_completion_tokens", "max_output_tokens")
+
+
+def _deployment(model_name: str) -> dict:
+    for entry in MODEL_LIST:
+        if entry["model_name"] == model_name:
+            return entry
+    raise ValueError(model_name)
+
+
+def _apply_capped(kwargs: dict) -> dict:
+    Router._apply_max_output_tokens_cap_to_request(deployment=_deployment("capped-model"), kwargs=kwargs)
+    return kwargs
+
+
+@pytest.mark.parametrize("field", BUDGET_FIELDS)
+def test_cap_lowers_oversized_budget(field):
+    kwargs = _apply_capped({field: 999_999})
+    assert kwargs[field] == 500
+
+
+@pytest.mark.parametrize("field", BUDGET_FIELDS)
+def test_cap_keeps_smaller_budget(field):
+    kwargs = _apply_capped({field: 200})
+    assert kwargs[field] == 200
+
+
+def test_cap_lowers_every_oversized_budget_in_one_request():
+    kwargs = _apply_capped(
+        {
+            "max_tokens": 999_999,
+            "max_completion_tokens": 50_000,
+            "max_output_tokens": 10_000,
+        }
+    )
+    assert kwargs["max_tokens"] == 500
+    assert kwargs["max_completion_tokens"] == 500
+    assert kwargs["max_output_tokens"] == 500
+
+
+def test_request_without_budget_is_untouched():
+    kwargs = _apply_capped({"messages": [{"role": "user", "content": "hi"}]})
+    assert "max_tokens" not in kwargs
+    assert "max_completion_tokens" not in kwargs
+    assert "max_output_tokens" not in kwargs
+
+
+def test_uncapped_deployment_is_untouched():
+    kwargs = {"max_tokens": 999_999}
+    Router._apply_max_output_tokens_cap_to_request(deployment=_deployment("uncapped-model"), kwargs=kwargs)
+    assert kwargs["max_tokens"] == 999_999
+
+
+def test_non_int_cap_values_are_ignored():
+    for bad_cap in ("500", 500.0, True, 0, -1, None):
+        deployment = {
+            "model_name": "capped-model",
+            "litellm_params": {"model": "openai/capped-model", "max_output_tokens_cap": bad_cap},
+        }
+        kwargs = {"max_tokens": 999_999}
+        Router._apply_max_output_tokens_cap_to_request(deployment=deployment, kwargs=kwargs)
+        assert kwargs["max_tokens"] == 999_999, bad_cap
+
+
+def test_pydantic_deployment_params_are_supported():
+    deployment = {
+        "model_name": "capped-model",
+        "litellm_params": LiteLLM_Params(
+            model="openai/capped-model",
+            api_base="http://localhost:9911/v1",
+            api_key="sk-not-real",
+            max_output_tokens_cap=500,
+        ),
+    }
+    kwargs = {"max_tokens": 999_999}
+    Router._apply_max_output_tokens_cap_to_request(deployment=deployment, kwargs=kwargs)
+    assert kwargs["max_tokens"] == 500
+
+
+def test_cap_applies_after_default_litellm_params_at_deployment_time():
+    """
+    End to end through Router._update_kwargs_with_deployment: a default
+    max_tokens from router default_litellm_params must also be clamped, so the
+    cap is a hard ceiling for every path that adds a budget.
+    """
+    router = Router(
+        model_list=MODEL_LIST,
+        default_litellm_params={"max_tokens": 999_999},
+    )
+    kwargs = {
+        "model": "capped-model",
+        "messages": [{"role": "user", "content": "hi"}],
+    }
+    router._update_kwargs_with_deployment(deployment=_deployment("capped-model"), kwargs=kwargs)
+    assert kwargs["max_tokens"] == 500  # default applied, then capped