From 75d95ec68e9435f4b83fb57501bc43bb87feb450 Mon Sep 17 00:00:00 2001
From: Raphael Fakhri <153192858+RaphaelFakhri@users.noreply.github.com>
Date: Tue, 3 Nov 2026 13:19:55 +0000
Subject: [PATCH] fix(client): copy custom headers before adding the session id

---
 src/deepgram/client.py                        | 20 +++++++++----------
 .../test_client_construction_and_helpers.py   | 13 ++++++++++++
 2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/src/deepgram/client.py b/src/deepgram/client.py
index 56e98d11..e1deb7ad 100644
--- a/src/deepgram/client.py
+++ b/src/deepgram/client.py
@@ -99,11 +99,11 @@ def __init__(self, *args, **kwargs) -> None:
         # Use provided session_id or generate one
         final_session_id = session_id if session_id is not None else str(uuid.uuid4())
 
-        # Ensure headers object exists for pass-through custom headers
-        headers: Optional[Dict[str, str]] = kwargs.get("headers")
-        if headers is None:
-            headers = {}
-            kwargs["headers"] = headers
+        # Copy pass-through custom headers so the session header below does not
+        # mutate the caller's dict (a dict shared by several clients would
+        # otherwise make every client send the last client's session id).
+        headers: Dict[str, str] = dict(kwargs.get("headers") or {})
+        kwargs["headers"] = headers
 
         # Ensure every request has a session identifier header
         headers["x-deepgram-session-id"] = final_session_id
@@ -183,11 +183,11 @@ def __init__(self, *args, **kwargs) -> None:
         # Use provided session_id or generate one
         final_session_id = session_id if session_id is not None else str(uuid.uuid4())
 
-        # Ensure headers object exists for pass-through custom headers
-        headers: Optional[Dict[str, str]] = kwargs.get("headers")
-        if headers is None:
-            headers = {}
-            kwargs["headers"] = headers
+        # Copy pass-through custom headers so the session header below does not
+        # mutate the caller's dict (a dict shared by several clients would
+        # otherwise make every client send the last client's session id).
+        headers: Dict[str, str] = dict(kwargs.get("headers") or {})
+        kwargs["headers"] = headers
 
         # Ensure every request has a session identifier header
         headers["x-deepgram-session-id"] = final_session_id
diff --git a/tests/custom/test_client_construction_and_helpers.py b/tests/custom/test_client_construction_and_helpers.py
index eb72c9d3..4a124488 100644
--- a/tests/custom/test_client_construction_and_helpers.py
+++ b/tests/custom/test_client_construction_and_helpers.py
@@ -62,6 +62,19 @@ def test_client_generates_session_id_and_opts_out_of_redaction(client_cls: typin
     assert client.session_id  # auto-generated UUID
 
 
+@pytest.mark.parametrize("client_cls", [DeepgramClient, AsyncDeepgramClient])
+def test_clients_sharing_a_headers_dict_keep_their_own_session_id(client_cls: typing.Any) -> None:
+    shared_headers = {"X-Custom": "value"}
+    first = client_cls(environment=_environment(), api_key="k", headers=shared_headers)
+    second = client_cls(environment=_environment(), api_key="k", headers=shared_headers)
+
+    for client in (first, second):
+        sent = client._client_wrapper.get_headers()
+        assert sent["x-deepgram-session-id"] == client.session_id
+        assert sent["X-Custom"] == "value"
+    assert shared_headers == {"X-Custom": "value"}
+
+
 @pytest.mark.parametrize("client_cls", [DeepgramClient, AsyncDeepgramClient])
 def test_client_with_transport_factory_disables_reconnect(client_cls: typing.Any) -> None:
     from deepgram.transport import restore_transport