Merge pull request #42119 from BerriAI/litellm_default_policy_attachments

* feat(policy_engine): add default fallback policy attachments

A policy attachment with default: true applies only when no non-default
attachment matches the request, so an opt-in guardrail policy replaces the
fallback one instead of running alongside it. Supported in config.yaml,
/policies/attachments, the Admin UI Attachments tab and the resolver
(matched_via is prefixed with default:).

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(policy_engine): ignore inapplicable non-default attachments when selecting defaults

A non-default attachment whose policy is missing or whose condition does not match the request
no longer suppresses default attachments. The impact preview marks default counts as an upper bound

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* refactor(policy_engine): accept any sequence of policy names in condition matching

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

* fix(policy_engine): resolve policies once and apply fallback semantics in get_matching_policies

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

---------

Co-authored-by: yucheng <yucheng@berri.ai>
Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm-proxy-extras/litellm_proxy_extras/migrations/20260920041500_add_policy_attachment_is_default/migration.sql

@@ -0,0 +1 @@
+ALTER TABLE "LiteLLM_PolicyAttachmentTable" ADD COLUMN IF NOT EXISTS "is_default" BOOLEAN NOT NULL DEFAULT false;

litellm-proxy-extras/litellm_proxy_extras/schema.prisma

@@ -1419,6 +1419,7 @@ model LiteLLM_PolicyAttachmentTable {
   models           String[]  @default([])  // Model names or patterns
   tags             String[]  @default([])  // Tag patterns (e.g., ["healthcare", "prod-*"])
   priority         Int?                    // Explicit execution order
+  is_default       Boolean   @default(false)  // Applied only when no non-default attachment matches
   created_at       DateTime  @default(now())
   created_by       String?
   updated_at       DateTime  @default(now()) @updatedAt

litellm/proxy/_lazy_openapi_snapshot.json

@@ -34982,6 +34982,12 @@
         "PolicyAttachmentCreateRequest": {
           "description": "Request body for creating a policy attachment.",
           "properties": {
+            "default": {
+              "default": false,
+              "description": "Apply this attachment only when no non-default attachment matches the request.",
+              "title": "Default",
+              "type": "boolean"
+            },
             "keys": {
               "anyOf": [
                 {
@@ -35113,6 +35119,12 @@
               "description": "Who created the attachment.",
               "title": "Created By"
             },
+            "default": {
+              "default": false,
+              "description": "Apply this attachment only when no non-default attachment matches the request.",
+              "title": "Default",
+              "type": "boolean"
+            },
             "definition_location": {
               "default": "db",
               "description": "Where this attachment is defined: 'db' (database) or 'config' (config.yaml).",
@@ -37141,6 +37153,12 @@
         "PolicyAttachmentCreateRequest": {
           "description": "Request body for creating a policy attachment.",
           "properties": {
+            "default": {
+              "default": false,
+              "description": "Apply this attachment only when no non-default attachment matches the request.",
+              "title": "Default",
+              "type": "boolean"
+            },
             "keys": {
               "anyOf": [
                 {

litellm/proxy/litellm_pre_call_utils.py

@@ -3216,7 +3216,9 @@ def _match_and_track_policies(
     attachment_registry: Final = (
         attachment_registry_override if attachment_registry_override is not None else get_attachment_registry()
     )
-    matches_with_reasons: Final = attachment_registry.get_attached_policies_with_reasons(context)
+    matches_with_reasons: Final = attachment_registry.get_attached_policies_with_reasons(
+        context, PolicyMatcher.policy_applies(context, policies_override)
+    )
     matching_policy_names: Final = [m["policy_name"] for m in matches_with_reasons]
     policy_reasons: Final = {m["policy_name"]: m["matched_via"] for m in matches_with_reasons}
 

litellm/proxy/policy_engine/attachment_registry.py

@@ -5,6 +5,7 @@ Attachments define WHERE policies apply, separate from the policy definitions.
 This allows the same policy to be attached to multiple scopes.
 """
 
+from collections.abc import Callable
 from datetime import datetime, timezone
 from types import MappingProxyType
 from typing import TYPE_CHECKING, Any, Final, TypedDict
@@ -119,35 +120,49 @@ class AttachmentRegistry:
             models=attachment_data.get("models"),
             tags=attachment_data.get("tags"),
             priority=attachment_data.get("priority"),
+            default=attachment_data.get("default", False),
         )
 
-    def get_attached_policies(self, context: PolicyMatchContext) -> list[str]:
+    def get_attached_policies(
+        self,
+        context: PolicyMatchContext,
+        policy_applies: Callable[[str], bool] | None = None,
+    ) -> list[str]:
         """
         Get list of policy names attached to the given context.
 
         Args:
             context: The request context to match against
+            policy_applies: Optional predicate; attachments whose policy does not apply are ignored
 
         Returns:
             List of policy names that are attached to matching scopes
         """
-        return [r["policy_name"] for r in self.get_attached_policies_with_reasons(context)]
+        return [r["policy_name"] for r in self.get_attached_policies_with_reasons(context, policy_applies)]
 
-    def get_attached_policies_with_reasons(self, context: PolicyMatchContext) -> list[PolicyAttachmentMatch]:
+    def get_attached_policies_with_reasons(
+        self,
+        context: PolicyMatchContext,
+        policy_applies: Callable[[str], bool] | None = None,
+    ) -> list[PolicyAttachmentMatch]:
         """
         Get list of policy names and match reasons for the given context.
 
         Returns a list of dicts with 'policy_name' and 'matched_via' keys.
         The 'matched_via' describes which dimension caused the match.
+        Attachments whose policy fails `policy_applies` are dropped before defaults are considered.
         """
         from litellm.proxy.policy_engine.policy_matcher import PolicyMatcher
 
+        in_scope: Final = tuple(
+            attachment
+            for attachment in self._attachments
+            if PolicyMatcher.scope_matches(scope=attachment.to_policy_scope(), context=context)
+            and (policy_applies is None or policy_applies(attachment.policy))
+        )
+        non_default: Final = tuple(attachment for attachment in in_scope if not attachment.default)
         matching_attachments: Final = sorted(
-            (
-                attachment
-                for attachment in self._attachments
-                if PolicyMatcher.scope_matches(scope=attachment.to_policy_scope(), context=context)
-            ),
+            non_default or tuple(attachment for attachment in in_scope if attachment.default),
             key=_attachment_sort_key,
         )
         broadest_attachment_by_policy: Final = MappingProxyType(
@@ -169,6 +184,11 @@ class AttachmentRegistry:
     @staticmethod
     def _describe_match_reason(attachment: PolicyAttachment, context: PolicyMatchContext) -> str:
         """Describe why an attachment matched the context."""
+        reason: Final = AttachmentRegistry._describe_scope_match(attachment, context)
+        return f"default:{reason}" if attachment.default else reason
+
+    @staticmethod
+    def _describe_scope_match(attachment: PolicyAttachment, context: PolicyMatchContext) -> str:
         from litellm.proxy.policy_engine.policy_matcher import PolicyMatcher
 
         if attachment.is_global():
@@ -324,6 +344,7 @@ class AttachmentRegistry:
                     "models": attachment_request.models or [],
                     "tags": attachment_request.tags or [],
                     "priority": attachment_request.priority,
+                    "is_default": attachment_request.default,
                     "created_at": datetime.now(timezone.utc),
                     "updated_at": datetime.now(timezone.utc),
                     "created_by": created_by,
@@ -340,6 +361,7 @@ class AttachmentRegistry:
                 models=attachment_request.models,
                 tags=attachment_request.tags,
                 priority=attachment_request.priority,
+                default=attachment_request.default,
             )
             self.add_attachment(attachment)
 
@@ -352,6 +374,7 @@ class AttachmentRegistry:
                 models=created_attachment.models or [],
                 tags=created_attachment.tags or [],
                 priority=created_attachment.priority,
+                default=created_attachment.is_default,
                 created_at=created_attachment.created_at,
                 updated_at=created_attachment.updated_at,
                 created_by=created_attachment.created_by,
@@ -429,6 +452,7 @@ class AttachmentRegistry:
                 models=attachment.models or [],
                 tags=attachment.tags or [],
                 priority=attachment.priority,
+                default=attachment.is_default,
                 created_at=attachment.created_at,
                 updated_at=attachment.updated_at,
                 created_by=attachment.created_by,
@@ -468,6 +492,7 @@ class AttachmentRegistry:
                     models=a.models or [],
                     tags=a.tags or [],
                     priority=a.priority,
+                    default=a.is_default,
                     created_at=a.created_at,
                     updated_at=a.updated_at,
                     created_by=a.created_by,
@@ -502,6 +527,7 @@ class AttachmentRegistry:
                     models=(attachment_response.models if attachment_response.models else None),
                     tags=attachment_response.tags if attachment_response.tags else None,
                     priority=attachment_response.priority,
+                    default=attachment_response.default,
                 )
                 for attachment_response in attachments
             ]

litellm/proxy/policy_engine/policy_endpoints.py

@@ -61,6 +61,7 @@ def _config_attachment_to_db_response(index: int, attachment: PolicyAttachment)
         models=attachment.models or [],
         tags=attachment.tags or [],
         priority=attachment.priority,
+        default=attachment.default,
         definition_location="config",
     )
 

litellm/proxy/policy_engine/policy_matcher.py

@@ -7,6 +7,7 @@ apply to a given request based on team alias, key alias, and model.
 Policies are matched via policy_attachments which define WHERE each policy applies.
 """
 
+from collections.abc import Callable, Sequence
 from typing import Final
 
 from litellm._logging import verbose_proxy_logger
@@ -113,7 +114,7 @@ class PolicyMatcher:
             verbose_proxy_logger.debug("AttachmentRegistry not initialized, returning empty list")
             return []
 
-        return registry.get_attached_policies(context)
+        return registry.get_attached_policies(context, PolicyMatcher.policy_applies(context))
 
     @staticmethod
     def get_matching_policies_from_registry(
@@ -130,9 +131,31 @@ class PolicyMatcher:
         """
         return PolicyMatcher.get_matching_policies(context=context)
 
+    @staticmethod
+    def policy_applies(
+        context: PolicyMatchContext,
+        policies: dict[str, Policy] | None = None,
+    ) -> Callable[[str], bool]:
+        """Predicate telling whether a policy exists and its condition matches the context."""
+        resolved: Final = policies if policies is not None else PolicyMatcher._registry_policies()
+        return lambda policy_name: bool(
+            PolicyMatcher.get_policies_with_matching_conditions(
+                policy_names=(policy_name,),
+                context=context,
+                policies=resolved,
+            )
+        )
+
+    @staticmethod
+    def _registry_policies() -> dict[str, Policy]:
+        from litellm.proxy.policy_engine.policy_registry import get_policy_registry
+
+        registry: Final = get_policy_registry()
+        return registry.get_all_policies() if registry.is_initialized() else {}
+
     @staticmethod
     def get_policies_with_matching_conditions(
-        policy_names: list[str],
+        policy_names: Sequence[str],
         context: PolicyMatchContext,
         policies: dict[str, Policy] | None = None,
     ) -> list[str]:
@@ -152,17 +175,12 @@ class PolicyMatcher:
             List of policy names whose conditions match the context
         """
         from litellm.proxy.policy_engine.condition_evaluator import ConditionEvaluator
-        from litellm.proxy.policy_engine.policy_registry import get_policy_registry
 
-        if policies is None:
-            registry: Final = get_policy_registry()
-            if not registry.is_initialized():
-                return []
-            policies = registry.get_all_policies()
+        resolved: Final = policies if policies is not None else PolicyMatcher._registry_policies()
 
         matching_policies: Final = []
         for policy_name in policy_names:
-            policy = policies.get(policy_name)
+            policy = resolved.get(policy_name)
             if policy is None:
                 continue
             # Policy matches if it has no condition OR condition evaluates to True

litellm/proxy/policy_engine/policy_resolve_endpoints.py

@@ -265,7 +265,9 @@ async def resolve_policies_for_context(
         )
 
         # Get matching policies with reasons
-        match_results: Final = get_attachment_registry().get_attached_policies_with_reasons(context=context)
+        match_results: Final = get_attachment_registry().get_attached_policies_with_reasons(
+            context=context, policy_applies=PolicyMatcher.policy_applies(context)
+        )
 
         if not match_results:
             return PolicyResolveResponse(

litellm/proxy/policy_engine/response_retrieval.py

@@ -84,7 +84,9 @@ def _retrieval_context(
 
 
 def _post_call_pipelines_for_context(context: PolicyMatchContext) -> tuple[PolicyPipelines, Mapping[str, str]]:
-    matches: Final = get_attachment_registry().get_attached_policies_with_reasons(context)
+    matches: Final = get_attachment_registry().get_attached_policies_with_reasons(
+        context, PolicyMatcher.policy_applies(context)
+    )
     if not matches:
         return (), MappingProxyType({})
     applied_policy_names: Final = PolicyMatcher.get_policies_with_matching_conditions(

litellm/proxy/schema.prisma

@@ -1419,6 +1419,7 @@ model LiteLLM_PolicyAttachmentTable {
   models           String[]  @default([])  // Model names or patterns
   tags             String[]  @default([])  // Tag patterns (e.g., ["healthcare", "prod-*"])
   priority         Int?                    // Explicit execution order
+  is_default       Boolean   @default(false)  // Applied only when no non-default attachment matches
   created_at       DateTime  @default(now())
   created_by       String?
   updated_at       DateTime  @default(now()) @updatedAt

litellm/types/proxy/policy_engine/policy_types.py

@@ -294,6 +294,10 @@ class PolicyAttachment(BaseModel):
         le=2147483647,
         description="Explicit execution order, lower runs first. Prioritised attachments run before those without one.",
     )
+    default: bool = Field(
+        default=False,
+        description="Apply this attachment only when no non-default attachment matches the request.",
+    )
 
     model_config = ConfigDict(extra="forbid")
 

litellm/types/proxy/policy_engine/resolver_types.py

@@ -311,6 +311,10 @@ class PolicyAttachmentCreateRequest(BaseModel):
         le=2147483647,
         description="Explicit execution order, lower runs first. Prioritised attachments run before those without one.",
     )
+    default: bool = Field(
+        default=False,
+        description="Apply this attachment only when no non-default attachment matches the request.",
+    )
 
 
 class PolicyAttachmentDBResponse(BaseModel):
@@ -327,6 +331,10 @@ class PolicyAttachmentDBResponse(BaseModel):
         default=None,
         description="Explicit execution order, lower runs first. Prioritised attachments run before those without one.",
     )
+    default: bool = Field(
+        default=False,
+        description="Apply this attachment only when no non-default attachment matches the request.",
+    )
     created_at: datetime | None = Field(default=None, description="When the attachment was created.")
     updated_at: datetime | None = Field(default=None, description="When the attachment was last updated.")
     created_by: str | None = Field(default=None, description="Who created the attachment.")

schema.prisma

@@ -1419,6 +1419,7 @@ model LiteLLM_PolicyAttachmentTable {
   models           String[]  @default([])  // Model names or patterns
   tags             String[]  @default([])  // Tag patterns (e.g., ["healthcare", "prod-*"])
   priority         Int?                    // Explicit execution order
+  is_default       Boolean   @default(false)  // Applied only when no non-default attachment matches
   created_at       DateTime  @default(now())
   created_by       String?
   updated_at       DateTime  @default(now()) @updatedAt

tests/test_litellm/proxy/policy_engine/test_attachment_registry.py

@@ -14,7 +14,8 @@ from litellm.proxy.policy_engine.attachment_registry import (
     AttachmentRegistry,
     get_attachment_registry,
 )
-from litellm.types.proxy.policy_engine import PolicyMatchContext
+from litellm.proxy.policy_engine.policy_matcher import PolicyMatcher
+from litellm.types.proxy.policy_engine import Policy, PolicyCondition, PolicyGuardrails, PolicyMatchContext
 
 
 class TestGetAttachedPolicies:
@@ -30,9 +31,7 @@ class TestGetAttachedPolicies:
         )
 
         # Should match any context
-        context = PolicyMatchContext(
-            team_alias="any-team", key_alias="any-key", model="any-model"
-        )
+        context = PolicyMatchContext(team_alias="any-team", key_alias="any-key", model="any-model")
         attached = registry.get_attached_policies(context)
         assert "global-baseline" in attached
 
@@ -46,15 +45,11 @@ class TestGetAttachedPolicies:
         )
 
         # Match
-        context = PolicyMatchContext(
-            team_alias="healthcare-team", key_alias="key", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="healthcare-team", key_alias="key", model="gpt-4")
         assert "healthcare-policy" in registry.get_attached_policies(context)
 
         # No match - different team
-        context_other = PolicyMatchContext(
-            team_alias="finance-team", key_alias="key", model="gpt-4"
-        )
+        context_other = PolicyMatchContext(team_alias="finance-team", key_alias="key", model="gpt-4")
         assert "healthcare-policy" not in registry.get_attached_policies(context_other)
 
     def test_key_wildcard_pattern_attachment(self):
@@ -67,15 +62,11 @@ class TestGetAttachedPolicies:
         )
 
         # Match - key starts with dev-key-
-        context = PolicyMatchContext(
-            team_alias="team", key_alias="dev-key-123", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="team", key_alias="dev-key-123", model="gpt-4")
         assert "dev-policy" in registry.get_attached_policies(context)
 
         # No match - different prefix
-        context_prod = PolicyMatchContext(
-            team_alias="team", key_alias="prod-key-123", model="gpt-4"
-        )
+        context_prod = PolicyMatchContext(team_alias="team", key_alias="prod-key-123", model="gpt-4")
         assert "dev-policy" not in registry.get_attached_policies(context_prod)
 
     def test_model_specific_attachment(self):
@@ -92,9 +83,7 @@ class TestGetAttachedPolicies:
         assert "gpt4-policy" in registry.get_attached_policies(context)
 
         # No match
-        context_other = PolicyMatchContext(
-            team_alias="team", key_alias="key", model="gpt-3.5"
-        )
+        context_other = PolicyMatchContext(team_alias="team", key_alias="key", model="gpt-3.5")
         assert "gpt4-policy" not in registry.get_attached_policies(context_other)
 
     def test_model_wildcard_pattern(self):
@@ -107,15 +96,11 @@ class TestGetAttachedPolicies:
         )
 
         # Match
-        context = PolicyMatchContext(
-            team_alias="team", key_alias="key", model="bedrock/claude-3"
-        )
+        context = PolicyMatchContext(team_alias="team", key_alias="key", model="bedrock/claude-3")
         assert "bedrock-policy" in registry.get_attached_policies(context)
 
         # No match
-        context_other = PolicyMatchContext(
-            team_alias="team", key_alias="key", model="openai/gpt-4"
-        )
+        context_other = PolicyMatchContext(team_alias="team", key_alias="key", model="openai/gpt-4")
         assert "bedrock-policy" not in registry.get_attached_policies(context_other)
 
     def test_multiple_attachments_match_same_context(self):
@@ -129,9 +114,7 @@ class TestGetAttachedPolicies:
             ]
         )
 
-        context = PolicyMatchContext(
-            team_alias="healthcare-team", key_alias="key", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="healthcare-team", key_alias="key", model="gpt-4")
         attached = registry.get_attached_policies(context)
 
         # All three should match
@@ -277,9 +260,7 @@ class TestGetAttachedPolicies:
             ]
         )
 
-        context = PolicyMatchContext(
-            team_alias="healthcare-team", key_alias="key", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="healthcare-team", key_alias="key", model="gpt-4")
         attached = registry.get_attached_policies(context)
 
         # Should only appear once
@@ -288,9 +269,7 @@ class TestGetAttachedPolicies:
     def test_many_distinct_policies_resolve_in_linear_time(self):
         policy_count = 20_000
         registry = AttachmentRegistry()
-        registry.load_attachments(
-            [{"policy": f"policy-{index}", "scope": "*"} for index in range(policy_count)]
-        )
+        registry.load_attachments([{"policy": f"policy-{index}", "scope": "*"} for index in range(policy_count)])
         context = PolicyMatchContext(team_alias="team", key_alias="key", model="gpt-4")
 
         started = time.perf_counter()
@@ -318,9 +297,7 @@ class TestGetAttachedPolicies:
             ]
         )
 
-        context = PolicyMatchContext(
-            team_alias="finance-team", key_alias="key", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="finance-team", key_alias="key", model="gpt-4")
         attached = registry.get_attached_policies(context)
         assert attached == []
 
@@ -338,23 +315,15 @@ class TestGetAttachedPolicies:
         )
 
         # Match - both team and model match
-        context = PolicyMatchContext(
-            team_alias="healthcare-team", key_alias="key", model="gpt-4"
-        )
+        context = PolicyMatchContext(team_alias="healthcare-team", key_alias="key", model="gpt-4")
         assert "strict-policy" in registry.get_attached_policies(context)
 
         # No match - team matches but model doesn't
-        context_wrong_model = PolicyMatchContext(
-            team_alias="healthcare-team", key_alias="key", model="gpt-3.5"
-        )
-        assert "strict-policy" not in registry.get_attached_policies(
-            context_wrong_model
-        )
+        context_wrong_model = PolicyMatchContext(team_alias="healthcare-team", key_alias="key", model="gpt-3.5")
+        assert "strict-policy" not in registry.get_attached_policies(context_wrong_model)
 
         # No match - model matches but team doesn't
-        context_wrong_team = PolicyMatchContext(
-            team_alias="finance-team", key_alias="key", model="gpt-4"
-        )
+        context_wrong_team = PolicyMatchContext(team_alias="finance-team", key_alias="key", model="gpt-4")
         assert "strict-policy" not in registry.get_attached_policies(context_wrong_team)
 
 
@@ -527,6 +496,111 @@ class TestMatchAttribution:
         assert "catch-all" in attached
 
 
+class TestDefaultAttachments:
+    """`default: true` attachments apply only when no non-default attachment matches."""
+
+    @staticmethod
+    def _registry() -> AttachmentRegistry:
+        registry = AttachmentRegistry()
+        registry.load_attachments(
+            [
+                {"policy": "guardrail-y", "scope": "*", "default": True},
+                {"policy": "guardrail-x", "tags": ["opt-in"]},
+            ]
+        )
+        return registry
+
+    def test_opted_in_request_gets_only_the_opt_in_policy(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.2", tags=["opt-in"])
+
+        assert self._registry().get_attached_policies(context) == ["guardrail-x"]
+
+    def test_request_without_opt_in_falls_back_to_default_policy(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.2")
+
+        assert self._registry().get_attached_policies(context) == ["guardrail-y"]
+
+    def test_default_attachment_still_honors_its_own_scope(self):
+        registry = AttachmentRegistry()
+        registry.load_attachments([{"policy": "team-default", "teams": ["team-a"], "default": True}])
+
+        assert registry.get_attached_policies(PolicyMatchContext(team_alias="team-a", key_alias="k", model="m")) == [
+            "team-default"
+        ]
+        assert registry.get_attached_policies(PolicyMatchContext(team_alias="team-b", key_alias="k", model="m")) == []
+
+    def test_all_matching_defaults_apply_when_nothing_else_matches(self):
+        registry = AttachmentRegistry()
+        registry.load_attachments(
+            [
+                {"policy": "default-a", "scope": "*", "default": True},
+                {"policy": "default-b", "teams": ["team-a"], "default": True},
+                {"policy": "opt-in", "tags": ["opt-in"]},
+            ]
+        )
+        context = PolicyMatchContext(team_alias="team-a", key_alias="k", model="m")
+
+        assert registry.get_attached_policies(context) == ["default-a", "default-b"]
+
+    def test_non_default_attachments_remain_additive(self):
+        registry = AttachmentRegistry()
+        registry.load_attachments(
+            [
+                {"policy": "baseline", "scope": "*"},
+                {"policy": "opt-in", "tags": ["opt-in"]},
+                {"policy": "fallback", "scope": "*", "default": True},
+            ]
+        )
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="m", tags=["opt-in"])
+
+        assert registry.get_attached_policies(context) == ["baseline", "opt-in"]
+
+    def test_default_match_reason_is_labelled(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="m")
+
+        results = self._registry().get_attached_policies_with_reasons(context)
+
+        assert results == [{"policy_name": "guardrail-y", "matched_via": "default:scope:*"}]
+
+    def test_inapplicable_opt_in_policy_does_not_suppress_default(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.2", tags=["opt-in"])
+        policies = {
+            "guardrail-y": Policy(guardrails=PolicyGuardrails(add=["y"])),
+            "guardrail-x": Policy(guardrails=PolicyGuardrails(add=["x"]), condition=PolicyCondition(model="claude.*")),
+        }
+
+        results = self._registry().get_attached_policies_with_reasons(
+            context, PolicyMatcher.policy_applies(context, policies)
+        )
+
+        assert results == [{"policy_name": "guardrail-y", "matched_via": "default:scope:*"}]
+
+    def test_attachment_to_missing_policy_does_not_suppress_default(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.2", tags=["opt-in"])
+        policies = {"guardrail-y": Policy(guardrails=PolicyGuardrails(add=["y"]))}
+
+        assert self._registry().get_attached_policies(context, PolicyMatcher.policy_applies(context, policies)) == [
+            "guardrail-y"
+        ]
+
+    def test_applicable_opt_in_policy_still_wins_with_predicate(self):
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.2", tags=["opt-in"])
+        policies = {
+            "guardrail-y": Policy(guardrails=PolicyGuardrails(add=["y"])),
+            "guardrail-x": Policy(guardrails=PolicyGuardrails(add=["x"]), condition=PolicyCondition(model="gpt.*")),
+        }
+
+        assert self._registry().get_attached_policies(context, PolicyMatcher.policy_applies(context, policies)) == [
+            "guardrail-x"
+        ]
+
+    def test_default_defaults_to_false_when_omitted(self):
+        registry = AttachmentRegistry()
+        registry.load_attachments([{"policy": "p"}])
+
+        assert registry.get_all_attachments()[0].default is False
+
+
 class TestAttachmentRegistrySingleton:
     """Test global singleton behavior."""
 
@@ -557,6 +631,7 @@ def _make_db_attachment_row(
     scope: str | None = None,
     teams: list[str] | None = None,
     priority: int | None = None,
+    is_default: bool = False,
 ) -> MagicMock:
     row = MagicMock()
     row.attachment_id = attachment_id
@@ -567,6 +642,7 @@ def _make_db_attachment_row(
     row.models = []
     row.tags = []
     row.priority = priority
+    row.is_default = is_default
     row.created_at = datetime.now(timezone.utc)
     row.updated_at = datetime.now(timezone.utc)
     row.created_by = None
@@ -576,9 +652,7 @@ def _make_db_attachment_row(
 
 def _prisma_with_attachment_rows(rows: list[MagicMock]) -> MagicMock:
     prisma = MagicMock()
-    prisma.configure_mock(
-        **{"db.litellm_policyattachmenttable.find_many": AsyncMock(return_value=rows)}
-    )
+    prisma.configure_mock(**{"db.litellm_policyattachmenttable.find_many": AsyncMock(return_value=rows)})
     return prisma
 
 
@@ -629,6 +703,15 @@ class TestConfigAttachmentsPreservedAcrossDbSync:
 
         assert registry.get_all_attachments()[0].priority == 7
 
+    @pytest.mark.asyncio
+    async def test_sync_round_trips_db_attachment_default_flag(self):
+        registry = AttachmentRegistry()
+        db_row = _make_db_attachment_row(is_default=True)
+
+        await registry.sync_attachments_from_db(_prisma_with_attachment_rows([db_row]))
+
+        assert registry.get_all_attachments()[0].default is True
+
     @pytest.mark.asyncio
     async def test_clear_removes_config_snapshot_so_sync_does_not_resurrect(self):
         registry = AttachmentRegistry()

tests/test_litellm/proxy/policy_engine/test_policy_matcher.py

@@ -8,8 +8,11 @@ Tests:
 
 import pytest
 
+import litellm.proxy.policy_engine.attachment_registry as attachment_registry_module
+import litellm.proxy.policy_engine.policy_registry as policy_registry_module
 from litellm.proxy.policy_engine.attachment_registry import AttachmentRegistry
 from litellm.proxy.policy_engine.policy_matcher import PolicyMatcher
+from litellm.proxy.policy_engine.policy_registry import PolicyRegistry
 from litellm.types.proxy.policy_engine import (
     PolicyMatchContext,
     PolicyScope,
@@ -196,3 +199,48 @@ class TestPolicyMatcherWithAttachments:
         attached = registry.get_attached_policies(context)
 
         assert "healthcare-policy" not in attached
+
+
+def _global_registries(monkeypatch):
+    policies = PolicyRegistry()
+    policies.load_policies(
+        {
+            "guardrail-y": {"guardrails": {"add": ["y"]}},
+            "guardrail-x": {"guardrails": {"add": ["x"]}, "condition": {"model": "claude.*"}},
+        }
+    )
+    attachments = AttachmentRegistry()
+    attachments.load_attachments(
+        [
+            {"policy": "guardrail-x", "tags": ["opt-in"]},
+            {"policy": "guardrail-y", "scope": "*", "default": True},
+        ]
+    )
+    monkeypatch.setattr(policy_registry_module, "get_policy_registry", lambda: policies)
+    monkeypatch.setattr(attachment_registry_module, "get_attachment_registry", lambda: attachments)
+    return policies
+
+
+class TestGetMatchingPoliciesFallback:
+    def test_condition_failing_opt_in_falls_back_to_default(self, monkeypatch):
+        _global_registries(monkeypatch)
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.5", tags=["opt-in"])
+
+        assert PolicyMatcher.get_matching_policies(context=context) == ["guardrail-y"]
+
+    def test_condition_passing_opt_in_suppresses_default(self, monkeypatch):
+        _global_registries(monkeypatch)
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="claude-haiku", tags=["opt-in"])
+
+        assert PolicyMatcher.get_matching_policies(context=context) == ["guardrail-x"]
+
+    def test_policy_applies_reads_registry_once(self, monkeypatch):
+        policies = _global_registries(monkeypatch)
+        calls = []
+        original = policies.get_all_policies
+        monkeypatch.setattr(policies, "get_all_policies", lambda: calls.append(1) or original())
+        context = PolicyMatchContext(team_alias="t", key_alias="k", model="gpt-5.5", tags=["opt-in"])
+
+        PolicyMatcher.get_matching_policies(context=context)
+
+        assert len(calls) == 1

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/AttachmentTable.test.tsx

@@ -65,6 +65,19 @@ describe("AttachmentTable", () => {
     );
   });
 
+  it("should show a Default badge only for default attachments", () => {
+    const attachments = [
+      makeAttachment({ attachment_id: "att-def00001", policy_name: "fallback", default: true }),
+      makeAttachment({ attachment_id: "att-def00002", policy_name: "regular" }),
+    ];
+    renderWithProviders(<AttachmentTable {...defaultProps} attachments={attachments} />);
+    const rows = screen.getAllByRole("row").slice(1);
+    const fallbackRow = rows.find((row) => within(row).queryByText("fallback"));
+    const regularRow = rows.find((row) => within(row).queryByText("regular"));
+    expect(within(fallbackRow!).getByText("Default")).toBeInTheDocument();
+    expect(within(regularRow!).queryByText("Default")).not.toBeInTheDocument();
+  });
+
   it("should show skeleton rows when isLoading is true", () => {
     renderWithProviders(<AttachmentTable {...defaultProps} isLoading />);
     expect(screen.getAllByTestId("skeleton-row").length).toBeGreaterThan(0);

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/AttachmentTableColumns.tsx

@@ -181,6 +181,20 @@ export const getAttachmentTableColumns = ({
         <span className="font-mono text-xs">{row.original.priority}</span>
       ),
   },
+  {
+    id: "default",
+    accessorFn: (row) => (row.default ? 1 : 0),
+    meta: { title: "Default" },
+    header: ({ column }) => <DataTableSortHeader column={column} title="Default" />,
+    size: 100,
+    enableSorting: true,
+    cell: ({ row }) =>
+      row.original.default ? (
+        <StatusBadge tone="info" label="Default" tooltip="Applied only when no non-default attachment matches" />
+      ) : (
+        <span className="text-muted-foreground">-</span>
+      ),
+  },
   {
     id: "created_at",
     accessorFn: (row) => row.created_at ?? "",

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/add_attachment_form.test.tsx

@@ -237,6 +237,21 @@ describe("AddAttachmentForm", () => {
     expect(createAttachment).toHaveBeenCalledWith("test-token", { policy_name: "policy-alpha", scope: "*" });
   });
 
+  it("sends default: true when the Default switch is turned on", async () => {
+    const user = userEvent.setup();
+    const createAttachment = vi.fn().mockResolvedValue({});
+    renderWithProviders(<AddAttachmentForm {...defaultProps} createAttachment={createAttachment} />);
+    await selectPolicy(user, "policy-alpha");
+    await user.click(screen.getByRole("switch", { name: /default/i }));
+    await submit(user);
+    await waitFor(() => expect(createAttachment).toHaveBeenCalledTimes(1));
+    expect(createAttachment).toHaveBeenCalledWith("test-token", {
+      policy_name: "policy-alpha",
+      scope: "*",
+      default: true,
+    });
+  });
+
   it.each([
     ["2147483648", /at most 2147483647/i],
     ["-2147483649", /at least -2147483648/i],

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/add_attachment_form.tsx

@@ -11,6 +11,7 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { RadioGroup, RadioGroupItem } from "@/components/ui/radio-group";
 import { Separator } from "@/components/ui/separator";
+import { Switch } from "@/components/ui/switch";
 import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from "@/components/ui/tooltip";
 import { UiLoadingSpinner } from "@/components/ui/ui-loading-spinner";
 import { useZodForm } from "@/lib/forms/useZodForm";
@@ -38,6 +39,7 @@ interface AttachmentFormValues {
   models: string[];
   tags: string[];
   priority: number | null;
+  default: boolean;
 }
 
 const EMPTY_VALUES: AttachmentFormValues = {
@@ -47,6 +49,7 @@ const EMPTY_VALUES: AttachmentFormValues = {
   models: [],
   tags: [],
   priority: null,
+  default: false,
 };
 
 const INT32_MIN = -2147483648;
@@ -64,6 +67,7 @@ const attachmentShape = {
     .min(INT32_MIN, `Priority must be at least ${INT32_MIN}`)
     .max(INT32_MAX, `Priority must be at most ${INT32_MAX}`)
     .nullable(),
+  default: z.boolean(),
 };
 
 const buildAttachmentSchema = (scopeType: ScopeType, teamsLoaded: boolean, availableTeams: string[]) =>
@@ -453,9 +457,23 @@ const AddAttachmentForm: React.FC<AddAttachmentFormProps> = ({
                   />
                 )}
               </FormField>
+
+              <FormField
+                control={form.control}
+                name="default"
+                label={labelWithHint(
+                  "Default (fallback)",
+                  "A default attachment is applied only when no non-default attachment matches the request.",
+                )}
+                description="Use this for the guardrail everyone gets unless they opt in to another attachment."
+              >
+                {({ value, onChange, ref, ...field }) => (
+                  <Switch {...field} inputRef={ref} checked={value === true} onCheckedChange={onChange} />
+                )}
+              </FormField>
             </FieldGroup>
 
-            {impactResult && <ImpactPreviewAlert impactResult={impactResult} />}
+            {impactResult && <ImpactPreviewAlert impactResult={impactResult} isDefault={form.watch("default")} />}
 
             <div className="flex justify-end space-x-2 mt-4">
               <Button type="button" variant="secondary" onClick={handleClose}>

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/build_attachment_data.test.ts

@@ -80,6 +80,16 @@ describe("buildAttachmentData", () => {
     });
   });
 
+  describe("default", () => {
+    it.each(["global", "specific"] as const)("should send default: true for a %s scope", (scopeType) => {
+      expect(buildAttachmentData({ policy_name: "p", default: true }, scopeType).default).toBe(true);
+    });
+
+    it.each([undefined, false])("should omit default when it is %s", (value) => {
+      expect(buildAttachmentData({ policy_name: "p", default: value }, "specific")).not.toHaveProperty("default");
+    });
+  });
+
   describe("priority", () => {
     it.each(["global", "specific"] as const)("should include priority for a %s scope", (scopeType) => {
       expect(buildAttachmentData({ policy_name: "p", priority: 0 }, scopeType).priority).toBe(0);

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/build_attachment_data.ts

@@ -7,6 +7,7 @@ export interface AttachmentFormInput {
   models?: string[];
   tags?: string[];
   priority?: number | null;
+  default?: boolean;
 }
 
 export function buildAttachmentData(
@@ -25,5 +26,6 @@ export function buildAttachmentData(
     if (formValues.tags && formValues.tags.length > 0) data.tags = formValues.tags;
   }
   if (typeof formValues.priority === "number") data.priority = formValues.priority;
+  if (formValues.default === true) data.default = true;
   return data;
 }

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/impact_preview_alert.test.tsx

@@ -69,6 +69,17 @@ describe("ImpactPreviewAlert", () => {
       expect(screen.getByText(/1 key\b/i)).toBeInTheDocument();
     });
 
+    it("should present the counts as an upper bound for a default attachment", () => {
+      renderWithProviders(<ImpactPreviewAlert impactResult={specificImpact} isDefault />);
+      expect(screen.getByText(/would affect up to/i)).toBeInTheDocument();
+      expect(screen.getByText(/no non-default attachment matches/i)).toBeInTheDocument();
+    });
+
+    it("should not qualify the counts for a non-default attachment", () => {
+      renderWithProviders(<ImpactPreviewAlert impactResult={specificImpact} />);
+      expect(screen.queryByText(/up to/i)).not.toBeInTheDocument();
+    });
+
     it("should not show a key section when there are no sample keys", () => {
       const noKeys = { affected_keys_count: 0, affected_teams_count: 2, sample_keys: [], sample_teams: ["t1", "t2"] };
       renderWithProviders(<ImpactPreviewAlert impactResult={noKeys} />);

ui/litellm-dashboard/src/app/(dashboard)/policies/_components/impact_preview_alert.tsx

@@ -12,6 +12,7 @@ interface ImpactResult {
 
 interface ImpactPreviewAlertProps {
   impactResult: ImpactResult;
+  isDefault?: boolean;
 }
 
 interface SampleListProps {
@@ -32,8 +33,9 @@ const SampleList: React.FC<SampleListProps> = ({ label, samples, totalCount }) =
   </div>
 );
 
-const ImpactPreviewAlert: React.FC<ImpactPreviewAlertProps> = ({ impactResult }) => {
+const ImpactPreviewAlert: React.FC<ImpactPreviewAlertProps> = ({ impactResult, isDefault = false }) => {
   const isGlobal = impactResult.affected_keys_count === -1;
+  const qualifier = isDefault ? "up to " : "";
 
   return (
     <Alert className="mb-4">
@@ -47,7 +49,7 @@ const ImpactPreviewAlert: React.FC<ImpactPreviewAlertProps> = ({ impactResult })
         ) : (
           <div>
             <span>
-              This attachment would affect{" "}
+              This attachment would affect {qualifier}
               <strong>
                 {impactResult.affected_keys_count} key{impactResult.affected_keys_count !== 1 ? "s" : ""}
               </strong>{" "}
@@ -57,6 +59,11 @@ const ImpactPreviewAlert: React.FC<ImpactPreviewAlertProps> = ({ impactResult })
               </strong>
               .
             </span>
+            {isDefault && (
+              <div className="text-xs text-muted-foreground">
+                Default attachments only apply to requests no non-default attachment matches, so fewer may be affected.
+              </div>
+            )}
             {impactResult.sample_keys.length > 0 && (
               <SampleList
                 label="Keys"

ui/litellm-dashboard/src/components/policies/types.ts

@@ -45,6 +45,7 @@ export interface PolicyAttachment {
   models: string[];
   tags: string[];
   priority?: number | null;
+  default?: boolean;
   created_at?: string;
   updated_at?: string;
   created_by?: string;
@@ -80,6 +81,7 @@ export interface PolicyAttachmentCreateRequest {
   models?: string[];
   tags?: string[];
   priority?: number;
+  default?: boolean;
 }
 
 export interface PolicyListResponse {

ui/litellm-dashboard/src/lib/http/schema.d.ts

@@ -35239,6 +35239,12 @@ export interface components {
          * @description Request body for creating a policy attachment.
          */
         PolicyAttachmentCreateRequest: {
+            /**
+             * Default
+             * @description Apply this attachment only when no non-default attachment matches the request.
+             * @default false
+             */
+            default: boolean;
             /**
              * Keys
              * @description Key aliases or patterns this attachment applies to.
@@ -35295,6 +35301,12 @@ export interface components {
              * @description Who created the attachment.
              */
             created_by?: string | null;
+            /**
+             * Default
+             * @description Apply this attachment only when no non-default attachment matches the request.
+             * @default false
+             */
+            default: boolean;
             /**
              * Definition Location
              * @description Where this attachment is defined: 'db' (database) or 'config' (config.yaml).