diff --git a/src/pipeline/gates.py b/src/pipeline/gates.py
index ddd894e3..a7bd8062 100644
--- a/src/pipeline/gates.py
+++ b/src/pipeline/gates.py
@@ -225,11 +225,44 @@ def check(self, recipe: RecipeSpec, ctx: GateContext) -> GateResult:
         return GateResult("regression", True, "at parity with registry")
 
 
+
+
+class BudgetGate(BaseGate):
+    """C3: declared performance budgets vs actual index values.
+
+    The index entry may declare perf budgets (size_mb today; latency
+    budgets ride the fixture decode in CI). A declared budget that the
+    actual artifact violates blocks the gate — regressions are release
+    failures, not notes."""
+
+    name = "budgets"
+
+    def check(self, recipe: RecipeSpec, ctx: GateContext) -> GateResult:
+        entry = (ctx.extra or {}).get("index_entry") or {}
+        perf = entry.get("perf") or {}
+        size_mb = perf.get("size_mb")
+        if size_mb is None:
+            return GateResult(self.name, True, "no perf budgets declared")
+        size = entry.get("size")
+        if size is None:
+            return GateResult(self.name, False,
+                              "perf.size_mb declared but index has no size")
+        actual_mb = size / 1_000_000
+        if actual_mb > float(size_mb):
+            return GateResult(self.name, False,
+                              f"artifact {actual_mb:.1f} MB exceeds the "
+                              f"declared {float(size_mb):.1f} MB budget")
+        return GateResult(self.name, True,
+                          f"{actual_mb:.1f} MB within the "
+                          f"{float(size_mb):.1f} MB budget")
+
+
 register_gate(QualityGate())
 register_gate(ParityGate())
 register_gate(LicenseGate())
 register_gate(ConformanceGate())
 register_gate(RegressionGate())
+register_gate(BudgetGate())
 
 
 def evaluate(
diff --git a/tests/test_pipeline_plan_gate.py b/tests/test_pipeline_plan_gate.py
index a4c702aa..13163f5a 100644
--- a/tests/test_pipeline_plan_gate.py
+++ b/tests/test_pipeline_plan_gate.py
@@ -157,6 +157,7 @@ def test_gate_results_files_end_to_end(tmp_path: Path) -> None:
         "license": True,
         "conformance": False,
         "regression": True,
+        "budgets": True,
     }
 
 
diff --git a/tests/test_pipeline_registry.py b/tests/test_pipeline_registry.py
index 8c0ff945..5ca84445 100644
--- a/tests/test_pipeline_registry.py
+++ b/tests/test_pipeline_registry.py
@@ -158,3 +158,20 @@ def test_license_policy_is_encapsulated() -> None:
     })
     strict = type(DEFAULT_LICENSE_POLICY)(allow_waivers=False)
     assert strict.blocked(restricted), "policies vary without core edits"
+
+
+def test_budget_gate_enforces_declared_size() -> None:
+    from pipeline.gates import BudgetGate, GateContext
+
+    gate = BudgetGate()
+    over = gate.check(None, GateContext(extra={"index_entry": {
+        "size": 100_000_000, "perf": {"size_mb": 50}}}))
+    assert not over.passed
+
+    ok = gate.check(None, GateContext(extra={"index_entry": {
+        "size": 40_000_000, "perf": {"size_mb": 50}}}))
+    assert ok.passed
+
+    no_budget = gate.check(None, GateContext(extra={"index_entry": {
+        "size": 1}}))
+    assert no_budget.passed  # nothing declared -> nothing to enforce