diff --git a/litellm/proxy/litellm_pre_call_utils.py b/litellm/proxy/litellm_pre_call_utils.py
index 15d1876e5a2..9ddc7ce2caf 100644
--- a/litellm/proxy/litellm_pre_call_utils.py
+++ b/litellm/proxy/litellm_pre_call_utils.py
@@ -45,6 +45,7 @@ _EXPLICIT_SESSION_HEADERS = frozenset({"x-litellm-trace-id", "x-litellm-session-
 # Session-id values must be non-empty strings of alphanumerics, hyphens, or underscores
 # (covers UUIDs and most common session-id formats).
 _SESSION_ID_VALUE_RE = re.compile(r"^[a-zA-Z0-9_\-]{8,}$")
+_ANTHROPIC_SESSION_ID_VALUE_RE = re.compile(r"^[a-zA-Z0-9_\-]+$")
 
 
 def _sanitize_for_log(value: Any) -> str:
@@ -426,6 +427,30 @@ def get_chain_id_from_headers(headers: Optional[Dict[str, str]]) -> Optional[str
     )
 
 
+def _get_anthropic_session_id_from_metadata(metadata: object) -> str | None:
+    if not isinstance(metadata, dict):
+        return None
+
+    user_id = metadata.get("user_id")
+    if isinstance(user_id, dict):
+        session_id = user_id.get("session_id")
+        if isinstance(session_id, str) and _ANTHROPIC_SESSION_ID_VALUE_RE.fullmatch(session_id):
+            return session_id
+        return None
+    if not isinstance(user_id, str):
+        return None
+
+    session_marker = "_session_"
+    session_marker_index = user_id.rfind(session_marker)
+    if session_marker_index == -1:
+        return None
+
+    session_id = user_id[session_marker_index + len(session_marker) :]
+    if not session_id or not _ANTHROPIC_SESSION_ID_VALUE_RE.fullmatch(session_id):
+        return None
+    return session_id
+
+
 def is_claude_code_user_agent(user_agent: str) -> bool:
     """Claude Code identifies itself as ``claude-cli/<version> ...``; the IDE
     extensions and the Agent SDK run through the same CLI and share that prefix."""
@@ -935,6 +960,15 @@ class LiteLLMProxyRequestSetup:
             data["litellm_session_id"] = chain_id
             data["litellm_trace_id"] = chain_id
             verbose_proxy_logger.debug(f"Extracted chain_id from header (trace-id/session-id): {chain_id}")
+        else:
+            body_metadata = data.get("metadata")
+            session_id = _get_anthropic_session_id_from_metadata(body_metadata)
+            if session_id:
+                metadata_from_headers["session_id"] = session_id
+                data["litellm_session_id"] = session_id
+                if isinstance(body_metadata, dict) and isinstance(body_metadata.get("user_id"), dict):
+                    body_metadata["user_id"] = session_id
+                verbose_proxy_logger.debug("Extracted session_id from Anthropic metadata.user_id")
 
         if isinstance(data[_metadata_variable_name], dict):
             data[_metadata_variable_name].update(metadata_from_headers)
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 d2b8b7ec23d..47879ee96ad 100644
--- a/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
+++ b/tests/test_litellm/proxy/test_litellm_pre_call_utils.py
@@ -2560,6 +2560,108 @@ def test_add_litellm_metadata_from_request_headers_generic_session_id_header():
     assert data["litellm_trace_id"] == "e96634a3-fa28-4083-b354-55542e2dca01"
 
 
+def test_add_litellm_metadata_from_anthropic_user_id_sets_session_id():
+    data = {
+        "metadata": {
+            "user_id": "user_abc123_account__session_e96634a3-fa28-4083-b354-55542e2dca01"
+        }
+    }
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={}, data=data, _metadata_variable_name="metadata"
+    )
+    assert data["metadata"]["session_id"] == "e96634a3-fa28-4083-b354-55542e2dca01"
+    assert data["litellm_session_id"] == "e96634a3-fa28-4083-b354-55542e2dca01"
+    assert "litellm_trace_id" not in data
+
+
+def test_add_litellm_metadata_from_anthropic_user_id_dict_sets_session_id():
+    data = {
+        "metadata": {
+            "user_id": {
+                "device_id": "device",
+                "account_uuid": "account",
+                "session_id": "sess_4f8c1d2a-1234",
+            }
+        }
+    }
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={}, data=data, _metadata_variable_name="metadata"
+    )
+    assert data["metadata"]["user_id"] == "sess_4f8c1d2a-1234"
+    assert data["metadata"]["session_id"] == "sess_4f8c1d2a-1234"
+    assert data["litellm_session_id"] == "sess_4f8c1d2a-1234"
+    assert "litellm_trace_id" not in data
+
+
+def test_add_litellm_metadata_from_headers_session_id_beats_anthropic_user_id():
+    data = {
+        "metadata": {
+            "user_id": "user_abc123_account__session_body-session-id",
+        }
+    }
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={"x-litellm-session-id": "header-session-id"},
+        data=data,
+        _metadata_variable_name="metadata",
+    )
+    assert data["metadata"]["session_id"] == "header-session-id"
+    assert data["litellm_session_id"] == "header-session-id"
+    assert data["litellm_trace_id"] == "header-session-id"
+
+
+def test_add_litellm_metadata_from_headers_session_id_beats_anthropic_user_id_dict():
+    data = {
+        "metadata": {
+            "user_id": {
+                "session_id": "body-session-id",
+            }
+        }
+    }
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={"x-litellm-session-id": "header-session-id"},
+        data=data,
+        _metadata_variable_name="metadata",
+    )
+    assert data["metadata"]["session_id"] == "header-session-id"
+    assert data["litellm_session_id"] == "header-session-id"
+    assert data["litellm_trace_id"] == "header-session-id"
+
+
+@pytest.mark.parametrize(
+    "user_id",
+    [
+        "user_abc123_account__session_",
+        "user_abc123_account_",
+        "user_abc123_account__session_invalid!",
+    ],
+)
+def test_add_litellm_metadata_from_anthropic_user_id_ignores_invalid_session_id(user_id: str):
+    data = {"metadata": {"user_id": user_id}}
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={}, data=data, _metadata_variable_name="metadata"
+    )
+    assert data == {"metadata": {"user_id": user_id}}
+
+
+@pytest.mark.parametrize(
+    "user_id",
+    [
+        {},
+        {"session_id": 123},
+        {"session_id": "invalid session id"},
+        {"session_id": ""},
+    ],
+)
+def test_add_litellm_metadata_from_anthropic_user_id_dict_ignores_invalid_session_id(
+    user_id: object,
+):
+    data = {"metadata": {"user_id": user_id}}
+    LiteLLMProxyRequestSetup.add_litellm_metadata_from_request_headers(
+        headers={}, data=data, _metadata_variable_name="metadata"
+    )
+    assert data == {"metadata": {"user_id": user_id}}
+
+
 def test_add_litellm_metadata_from_request_headers_explicit_header_beats_generic():
     """Explicit x-litellm-trace-id wins over a generic x-*-session-id header."""
     headers = {