From 0128081e17c2002c67ce22a348bd571e0f505952 Mon Sep 17 00:00:00 2001
From: Sahil <sahilkhan.jodhpur786@gmail.com>
Date: Tue, 7 Apr 2026 03:31:45 +0530
Subject: [PATCH] fix: ensure session_id stays consistent when body sets
 trace_id but not session_id

---
 litellm/proxy/litellm_pre_call_utils.py       | 23 +++++++++++--------
 .../proxy/test_litellm_pre_call_utils.py      |  1 +
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/litellm/proxy/litellm_pre_call_utils.py b/litellm/proxy/litellm_pre_call_utils.py
index 22546a92af3..52979222b4b 100644
--- a/litellm/proxy/litellm_pre_call_utils.py
+++ b/litellm/proxy/litellm_pre_call_utils.py
@@ -660,20 +660,25 @@ class LiteLLMProxyRequestSetup:
         if chain_id:
             metadata_from_headers["trace_id"] = chain_id
             metadata_from_headers["session_id"] = chain_id
-            # Only prefer body trace_id on litellm_metadata routes (/v1/messages, threads, etc.)
+            # Only prefer body values on litellm_metadata routes (/v1/messages, threads, etc.)
             # On /chat/completions, metadata["trace_id"] belongs to observability tools
             # (e.g. LangFuse) and should not override the header chain ID.
             _body_trace_id: Optional[str] = None
+            _body_session_id: Optional[str] = None
             if _metadata_variable_name == "litellm_metadata":
                 _body_metadata = data.get(_metadata_variable_name)
-                _body_trace_id = (
-                    _body_metadata.get("trace_id")
-                    if isinstance(_body_metadata, dict)
-                    else None
-                )
-            effective_id = _body_trace_id or chain_id
-            data["litellm_session_id"] = effective_id
-            data["litellm_trace_id"] = effective_id
+                if isinstance(_body_metadata, dict):
+                    _body_trace_id = _body_metadata.get("trace_id")
+                    _body_session_id = _body_metadata.get("session_id")
+            effective_trace_id = _body_trace_id or chain_id
+            # session_id mirrors trace_id when not explicitly set in the body
+            effective_session_id = _body_session_id or _body_trace_id or chain_id
+            data["litellm_session_id"] = effective_session_id
+            data["litellm_trace_id"] = effective_trace_id
+            # Sync metadata_from_headers so the merge loop below injects
+            # consistent values when the body doesn't set these keys.
+            metadata_from_headers["trace_id"] = effective_trace_id
+            metadata_from_headers["session_id"] = effective_session_id
             verbose_proxy_logger.debug(
                 f"Extracted chain_id from header (trace-id/session-id): {chain_id}"
             )
diff --git a/tests/test_litellm/proxy/test_litellm_pre_call_utils.py b/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
index 55f0ae7c9cf..7853f467bab 100644
--- a/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
+++ b/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
@@ -1972,6 +1972,7 @@ class TestAddLitellmMetadataFromRequestHeaders:
         )
 
         assert result["litellm_metadata"]["trace_id"] == "from-body"
+        assert result["litellm_metadata"]["session_id"] == "from-body"  # must mirror trace_id
         assert result["litellm_session_id"] == "from-body"
         assert result["litellm_trace_id"] == "from-body"