diff --git a/litellm/router_strategy/complexity_router/README.md b/litellm/router_strategy/complexity_router/README.md
index cf7bde93360..3aea7a6e482 100644
--- a/litellm/router_strategy/complexity_router/README.md
+++ b/litellm/router_strategy/complexity_router/README.md
@@ -29,10 +29,10 @@ The weighted sum is mapped to tiers using configurable boundaries:
 
 | Tier | Score Range | Boundary key below it | Typical Use |
 |------|-------------|-----------------------|-------------|
-| SIMPLE | < 0.15 | - | Basic questions, greetings |
-| MEDIUM | 0.15 - 0.35 | `simple_medium` | Standard queries |
-| COMPLEX | 0.35 - 0.60 | `medium_complex` | Technical, multi-part requests |
-| REASONING | > 0.60 | `complex_reasoning` | Chain-of-thought, analysis |
+| SIMPLE | < 0.10 | - | Basic questions, greetings |
+| MEDIUM | 0.10 - 0.25 | `simple_medium` | Standard queries |
+| COMPLEX | 0.25 - 0.50 | `medium_complex` | Technical, multi-part requests |
+| REASONING | > 0.50 | `complex_reasoning` | Chain-of-thought, analysis |
 
 Tier names are defaults you can rename with [`tier_labels`](#renaming-the-tiers). The three `tier_boundaries` keys are named after those defaults but they are scorer knobs, not tiers: each one names the gap between two rungs and is persisted by name on every routing decision, so they stay `simple_medium` / `medium_complex` / `complex_reasoning` no matter what you call the tiers. The column above tells a renamed deployment which knob it is turning.
 
@@ -120,9 +120,9 @@ model_list:
         
         # Tier boundaries (normalized scores)
         tier_boundaries:
-          simple_medium: 0.15
-          medium_complex: 0.35
-          complex_reasoning: 0.60
+          simple_medium: 0.10
+          medium_complex: 0.25
+          complex_reasoning: 0.50
         
         # Token count thresholds
         token_thresholds:
diff --git a/litellm/router_strategy/complexity_router/complexity_router.py b/litellm/router_strategy/complexity_router/complexity_router.py
index cbaba69f696..7420c3afb7c 100644
--- a/litellm/router_strategy/complexity_router/complexity_router.py
+++ b/litellm/router_strategy/complexity_router/complexity_router.py
@@ -48,6 +48,7 @@ from .config import (
     DEFAULT_REASONING_KEYWORDS,
     DEFAULT_SIMPLE_KEYWORDS,
     DEFAULT_TECHNICAL_KEYWORDS,
+    DEFAULT_TIER_BOUNDARIES,
     PLAN_MODE_SYSTEM_SENTINELS,
     PLAN_MODE_TAIL_SENTINELS,
     PLAN_MODE_TOOL_NAME,
@@ -1097,9 +1098,9 @@ class ComplexityRouter(CustomLogger):
         """
         boundaries: Final = self.config.tier_boundaries
         return StandardLoggingRoutingDecisionTierBoundaries(
-            simple_medium=boundaries.get("simple_medium", 0.15),
-            medium_complex=boundaries.get("medium_complex", 0.35),
-            complex_reasoning=boundaries.get("complex_reasoning", 0.60),
+            simple_medium=boundaries.get("simple_medium", DEFAULT_TIER_BOUNDARIES["simple_medium"]),
+            medium_complex=boundaries.get("medium_complex", DEFAULT_TIER_BOUNDARIES["medium_complex"]),
+            complex_reasoning=boundaries.get("complex_reasoning", DEFAULT_TIER_BOUNDARIES["complex_reasoning"]),
         )
 
     def _build_routing_decision(
diff --git a/litellm/router_strategy/complexity_router/config.py b/litellm/router_strategy/complexity_router/config.py
index d3c4bd7938b..10906f14bda 100644
--- a/litellm/router_strategy/complexity_router/config.py
+++ b/litellm/router_strategy/complexity_router/config.py
@@ -366,9 +366,9 @@ DEFAULT_DIMENSION_WEIGHTS: Final[dict[str, float]] = {
 # ─── Default Tier Boundaries ───
 
 DEFAULT_TIER_BOUNDARIES: Final[dict[str, float]] = {
-    "simple_medium": 0.15,  # Lower threshold to catch more MEDIUM cases
-    "medium_complex": 0.35,  # Lower threshold to catch technical COMPLEX cases
-    "complex_reasoning": 0.60,  # Reasoning tier reserved for explicit reasoning markers
+    "simple_medium": 0.10,
+    "medium_complex": 0.25,
+    "complex_reasoning": 0.50,
 }
 
 
diff --git a/tests/test_litellm/router_strategy/test_complexity_router.py b/tests/test_litellm/router_strategy/test_complexity_router.py
index 64b60c75f87..3e14c462f9e 100644
--- a/tests/test_litellm/router_strategy/test_complexity_router.py
+++ b/tests/test_litellm/router_strategy/test_complexity_router.py
@@ -37,6 +37,7 @@ from litellm.router_strategy.complexity_router.config import (
     DEFAULT_CLASSIFIER_CONTEXT_WINDOW_SIZE,
     DEFAULT_COMPLEXITY_CONFIG,
     DEFAULT_TECHNICAL_KEYWORDS,
+    DEFAULT_TIER_BOUNDARIES,
     ClassifierLLMConfig,
     ComplexityRouterConfig,
     ComplexityTier,
@@ -602,6 +603,44 @@ class TestPreRoutingHook:
         assert result.model == "o1-preview"  # REASONING tier model
 
 
+class TestEffectiveTierBoundaries:
+    """Test how configured boundaries resolve against the shipped defaults."""
+
+    def test_unconfigured_boundaries_resolve_to_the_shipped_defaults(self, mock_router_instance):
+        """A router with no tier_boundaries runs on DEFAULT_TIER_BOUNDARIES, not on stale literals."""
+        router = ComplexityRouter(
+            model_name="test-complexity-router",
+            litellm_router_instance=mock_router_instance,
+            complexity_router_config={"tiers": {"SIMPLE": "a", "MEDIUM": "b", "COMPLEX": "c", "REASONING": "d"}},
+        )
+        assert dict(router._effective_tier_boundaries()) == DEFAULT_TIER_BOUNDARIES
+
+    def test_partial_boundaries_fill_missing_keys_from_the_defaults(self, mock_router_instance):
+        """Overriding one boundary must not strand the other two on a second, drifting copy of the defaults."""
+        router = ComplexityRouter(
+            model_name="test-complexity-router",
+            litellm_router_instance=mock_router_instance,
+            complexity_router_config={
+                "tiers": {"SIMPLE": "a", "MEDIUM": "b", "COMPLEX": "c", "REASONING": "d"},
+                "tier_boundaries": {"simple_medium": 0.42},
+            },
+        )
+        assert dict(router._effective_tier_boundaries()) == {
+            "simple_medium": 0.42,
+            "medium_complex": DEFAULT_TIER_BOUNDARIES["medium_complex"],
+            "complex_reasoning": DEFAULT_TIER_BOUNDARIES["complex_reasoning"],
+        }
+
+    def test_defaults_stay_ordered_and_within_the_scoring_range(self):
+        """The tiers only all remain reachable while the boundaries ascend."""
+        simple_medium, medium_complex, complex_reasoning = (
+            DEFAULT_TIER_BOUNDARIES["simple_medium"],
+            DEFAULT_TIER_BOUNDARIES["medium_complex"],
+            DEFAULT_TIER_BOUNDARIES["complex_reasoning"],
+        )
+        assert 0 < simple_medium < medium_complex < complex_reasoning < 1
+
+
 class TestConfigOverrides:
     """Test configuration override functionality."""
 
@@ -5074,7 +5113,7 @@ class TestRoutingDecisionContents:
         assert isinstance(decision["score"], float)
         assert any("short" in signal for signal in decision["signals"])
         # The snapshot must reflect the CONFIGURED boundaries (the fixture overrides the
-        # 0.15/0.35/0.60 defaults), so a logged row stays truthful after config edits.
+        # shipped defaults), so a logged row stays truthful after config edits.
         assert decision["tier_boundaries"] == {
             "simple_medium": 0.25,
             "medium_complex": 0.50,
diff --git a/tests/test_litellm/router_strategy/test_quality_router.py b/tests/test_litellm/router_strategy/test_quality_router.py
index a54e95ff7a1..f55f557bbb5 100644
--- a/tests/test_litellm/router_strategy/test_quality_router.py
+++ b/tests/test_litellm/router_strategy/test_quality_router.py
@@ -408,7 +408,7 @@ class TestPreRoutingHook:
         request in the session, and carries no signal about how requests differ. Before
         the fix this system prompt alone supplied 5 codePresence + 2 technicalTerms
         keyword matches, saturating both dimensions and crossing the default
-        simple_medium boundary (0.15) purely from harness text, independent of the ask."""
+        simple_medium boundary purely from harness text, independent of the ask."""
         agent_system_prompt = (
             "You are Claude Code, Anthropic's official CLI for Claude.\n"
             "You are an interactive agent that helps users with software engineering tasks.\n\n"
diff --git a/ui/litellm-dashboard/src/components/add_model/ComplexityRouterConfig.test.tsx b/ui/litellm-dashboard/src/components/add_model/ComplexityRouterConfig.test.tsx
index 0a848ed7deb..ef3c954f630 100644
--- a/ui/litellm-dashboard/src/components/add_model/ComplexityRouterConfig.test.tsx
+++ b/ui/litellm-dashboard/src/components/add_model/ComplexityRouterConfig.test.tsx
@@ -69,10 +69,10 @@ describe("ComplexityRouterConfig", () => {
   it("should show score thresholds in the classification section", () => {
     renderWithProviders(<ComplexityRouterConfig {...baseProps} />);
     fireEvent.click(screen.getByText("Advanced: Classification Method"));
-    expect(screen.getByText(/Score < 0.15/)).toBeInTheDocument();
-    expect(screen.getByText(/Score 0.15 - 0.35/)).toBeInTheDocument();
-    expect(screen.getByText(/Score 0.35 - 0.60/)).toBeInTheDocument();
-    expect(screen.getByText(/Score > 0.60/)).toBeInTheDocument();
+    expect(screen.getByText(/Score < 0.10/)).toBeInTheDocument();
+    expect(screen.getByText(/Score 0.10 - 0.25/)).toBeInTheDocument();
+    expect(screen.getByText(/Score 0.25 - 0.50/)).toBeInTheDocument();
+    expect(screen.getByText(/Score > 0.50/)).toBeInTheDocument();
   });
 
   it("should default to heuristic and hide classifier model/timeout fields", () => {
diff --git a/ui/litellm-dashboard/src/components/add_model/HeuristicScoringConfig.test.tsx b/ui/litellm-dashboard/src/components/add_model/HeuristicScoringConfig.test.tsx
index 9dccd767e49..bc2c155711b 100644
--- a/ui/litellm-dashboard/src/components/add_model/HeuristicScoringConfig.test.tsx
+++ b/ui/litellm-dashboard/src/components/add_model/HeuristicScoringConfig.test.tsx
@@ -41,7 +41,7 @@ describe("HeuristicScoringConfig", () => {
   it("prefills the shipped defaults", async () => {
     await render(BASE);
 
-    expect(screen.getByLabelText("Simple to Medium")).toHaveValue("0.15");
+    expect(screen.getByLabelText("Simple to Medium")).toHaveValue("0.1");
     expect(screen.getByLabelText("Long above")).toHaveValue("400");
     expect(screen.getByTestId("dimension-weight-total")).toHaveTextContent("total 1.00");
   });
@@ -57,8 +57,8 @@ describe("HeuristicScoringConfig", () => {
 
     expect((onChange.mock.calls.at(-1)?.[0] as ComplexityRouterConfigValue).tier_boundaries).toEqual({
       simple_medium: 0.22,
-      medium_complex: 0.35,
-      complex_reasoning: 0.6,
+      medium_complex: 0.25,
+      complex_reasoning: 0.5,
     });
   });
 
@@ -184,7 +184,7 @@ describe("ClassificationMethodConfig scorer gating", () => {
 
     expect(screen.getByText(/Score < 0.22/)).toBeInTheDocument();
     expect(screen.getByText(/Score 0.44 - 0.66/)).toBeInTheDocument();
-    expect(screen.queryByText(/0.15/)).not.toBeInTheDocument();
+    expect(screen.queryByText(/0.10/)).not.toBeInTheDocument();
   });
 
   it("states the configured override floor in the reasoning-marker aside, not the boundary", () => {
@@ -196,7 +196,7 @@ describe("ClassificationMethodConfig scorer gating", () => {
   it("falls back to the Simple to Medium boundary when no override floor is set", () => {
     renderWithProviders(<ClassificationMethodConfig {...props} value={BASE} />);
 
-    expect(screen.getByText(/2\+ reasoning markers with a score of at least 0\.15/)).toBeInTheDocument();
+    expect(screen.getByText(/2\+ reasoning markers with a score of at least 0\.10/)).toBeInTheDocument();
   });
 
   it("renders a row for every scored dimension", async () => {
diff --git a/ui/litellm-dashboard/tests/mocks/complexityScorerDefaults.ts b/ui/litellm-dashboard/tests/mocks/complexityScorerDefaults.ts
index 3eb2d781213..507d8d65f72 100644
--- a/ui/litellm-dashboard/tests/mocks/complexityScorerDefaults.ts
+++ b/ui/litellm-dashboard/tests/mocks/complexityScorerDefaults.ts
@@ -10,7 +10,7 @@ import type { ComplexityScorerDefaults } from "@/components/networking";
  * which is how the failure path is covered.
  */
 export const SHIPPED_SCORER_DEFAULTS: ComplexityScorerDefaults = {
-  tier_boundaries: { simple_medium: 0.15, medium_complex: 0.35, complex_reasoning: 0.6 },
+  tier_boundaries: { simple_medium: 0.1, medium_complex: 0.25, complex_reasoning: 0.5 },
   token_thresholds: { simple: 15, complex: 400 },
   dimension_weights: {
     codePresence: 0.3,