fix(langchain): skip priority-tier keys when subtracting token detail counts (#1549)

Author: Br1an67

langfuse/langchain/CallbackHandler.py

@@ -1189,6 +1189,10 @@ def _parse_usage_model(usage: Union[pydantic.BaseModel, dict]) -> Any:
             for key, value in input_token_details.items():
                 usage_model[f"input_{key}"] = value
 
+                # Skip priority-tier keys as they are not exclusive sub-categories
+                if key == "priority" or key.startswith("priority_"):
+                    continue
+
                 if "input" in usage_model:
                     usage_model["input"] = max(0, usage_model["input"] - value)
 
@@ -1198,6 +1202,10 @@ def _parse_usage_model(usage: Union[pydantic.BaseModel, dict]) -> Any:
             for key, value in output_token_details.items():
                 usage_model[f"output_{key}"] = value
 
+                # Skip priority-tier keys as they are not exclusive sub-categories
+                if key == "priority" or key.startswith("priority_"):
+                    continue
+
                 if "output" in usage_model:
                     usage_model["output"] = max(0, usage_model["output"] - value)
 

tests/test_parse_usage_model.py

@@ -0,0 +1,34 @@
+from langfuse.langchain.CallbackHandler import _parse_usage_model
+
+
+def test_standard_tier_input_token_details():
+    """Standard tier: audio and cache_read are subtracted from input."""
+    usage = {
+        "input_tokens": 13,
+        "output_tokens": 1,
+        "total_tokens": 14,
+        "input_token_details": {"audio": 0, "cache_read": 3},
+        "output_token_details": {"audio": 0},
+    }
+    result = _parse_usage_model(usage)
+    assert result["input"] == 10  # 13 - 0 (audio) - 3 (cache_read)
+    assert result["output"] == 1  # 1 - 0 (audio)
+    assert result["total"] == 14
+
+
+def test_priority_tier_not_subtracted():
+    """Priority tier: 'priority' and 'priority_*' keys must NOT be subtracted."""
+    usage = {
+        "input_tokens": 13,
+        "output_tokens": 1,
+        "total_tokens": 14,
+        "input_token_details": {"audio": 0, "priority_cache_read": 0, "priority": 13},
+        "output_token_details": {"audio": 0, "priority_reasoning": 0, "priority": 1},
+    }
+    result = _parse_usage_model(usage)
+    assert result["input"] == 13  # priority keys not subtracted
+    assert result["output"] == 1
+    assert result["total"] == 14
+    # Priority keys are still stored with prefixed names
+    assert result["input_priority"] == 13
+    assert result["output_priority"] == 1