diff --git a/openpilot/starpilot/flm/live_tracking_response.py b/openpilot/starpilot/flm/live_tracking_response.py
index 3a4df3fb2e..7bf546af73 100644
--- a/openpilot/starpilot/flm/live_tracking_response.py
+++ b/openpilot/starpilot/flm/live_tracking_response.py
@@ -138,11 +138,11 @@ def _source_key(context):
 _VALID_SOURCE_CONTEXTS = OrderedDict()
 
 
-def validate_source_context(context):
+def _validated_source_key(context):
   key = _source_key(context)
   if key in _VALID_SOURCE_CONTEXTS:
     _VALID_SOURCE_CONTEXTS.move_to_end(key)
-    return context
+    return key
   context.binding.validate()
   if (
     context.version != SOURCE_VERSION
@@ -165,6 +165,11 @@ def validate_source_context(context):
   _VALID_SOURCE_CONTEXTS[key] = None
   if len(_VALID_SOURCE_CONTEXTS) > 8:
     _VALID_SOURCE_CONTEXTS.popitem(last=False)
+  return key
+
+
+def validate_source_context(context):
+  _validated_source_key(context)
   return context
 
 
@@ -424,11 +429,23 @@ class ResponseWitness:
 def _validate_raw_witness(witness, binding, now_ns, *, content=True):
   if type(witness) is not ResponseWitness:
     raise ValueError('fresh source physical residual witness required')
-  cert = validate_certificate(witness.certificate) if content else witness.certificate
+  owned = _owned(witness, ResponseWitness, _WITNESS_FIELDS)
+  cert = owned['certificate']
+  source_key = _validated_source_key(cert) if content and type(cert) is TrackingSourceContext else None
+  if content and source_key is None:
+    cert = validate_certificate(cert)
   source_only = type(cert) is TrackingSourceContext
+  # Share immutable values only within this call. Every new call still checks
+  # the actual dictionaries/accessors, expected binding and original clocks.
+  cert_binding = cert.binding
+  cert_values = source_key[1] if source_key is not None else _binding_values(cert_binding)
+  expected = cert_values if binding is cert_binding else _binding_values(binding)
+  actual_binding = owned['binding']
+  actual = (cert_values if actual_binding is cert_binding else
+            expected if actual_binding is binding else _binding_values(actual_binding))
   if (
-    _binding_values(witness.binding) != _binding_values(binding)
-    or _binding_values(cert.binding) != _binding_values(binding)
+    actual != expected
+    or cert_values != expected
     or any(
       type(v) is not int
       for v in (
diff --git a/openpilot/starpilot/flm/tests/test_witness_binding_values.py b/openpilot/starpilot/flm/tests/test_witness_binding_values.py
new file mode 100644
index 0000000000..72ed2ef529
--- /dev/null
+++ b/openpilot/starpilot/flm/tests/test_witness_binding_values.py
@@ -0,0 +1,35 @@
+"""Per-call binding validation deduplicates identities, never clocks or grants."""
+from dataclasses import replace
+import pytest
+from openpilot.starpilot.flm import live_tracking_response as response
+from openpilot.starpilot.flm.tests.test_tracking_source_context import context
+
+
+@pytest.mark.parametrize('same_witness,same_expected', [(True, True), (False, True), (True, False), (False, False)])
+def test_each_distinct_binding_validated_once_per_witness_call(monkeypatch, same_witness, same_expected):
+  certificate = context()
+  now = 10_000_000_000
+  actual = certificate.binding if same_witness else replace(certificate.binding)
+  expected = certificate.binding if same_expected else replace(certificate.binding)
+  raw = response.ResponseWitness(certificate, actual, now-certificate.lag_ns,
+    now-certificate.lag_ns, now, now-350_000_000, 8, None, now+100_000_000)
+  calls = []
+  original = response._binding_values
+  def measured(value):
+    calls.append(value)
+    return original(value)
+  monkeypatch.setattr(response, '_binding_values', measured)
+  assert response.validate_response_witness(raw, expected, now) is raw
+  assert len(calls) == len({id(actual), id(expected), id(certificate.binding)})
+
+
+def test_binding_deduplication_does_not_reuse_a_previous_call():
+  certificate = context()
+  now = 10_000_000_000
+  raw = response.ResponseWitness(certificate, certificate.binding, now-certificate.lag_ns,
+    now-certificate.lag_ns, now, now-350_000_000, 8, None, now+100_000_000)
+  assert response.validate_response_witness(raw, certificate.binding, now) is raw
+  with pytest.raises(ValueError):
+    response.validate_response_witness(raw, certificate.binding, now+100_000_001)
+  with pytest.raises(ValueError):
+    response.validate_response_witness(raw, replace(certificate.binding, source_epoch='0'*64), now)
diff --git a/prebuilt.json b/prebuilt.json
index 4d0fa511d0..23437ff0dc 100644
--- a/prebuilt.json
+++ b/prebuilt.json
@@ -1 +1 @@
-{"protected_inventory_sha256": "7f8eb67a69cd1ecbdcbabd4305fd8e2cb8c86c0e1185710d118e22210091159a", "schema_version": 1}
+{"protected_inventory_sha256": "df20c562268a9a77c5f28cebfefaf91594010416c0a50ef59bdcf8f3bc759bb5", "schema_version": 1}