diff --git a/openapi_python_sdk/client.py b/openapi_python_sdk/client.py
index 18b6341..4ba5211 100644
--- a/openapi_python_sdk/client.py
+++ b/openapi_python_sdk/client.py
@@ -1,4 +1,5 @@
 import json
+import threading
 from typing import Any, Dict
 
 import httpx
@@ -15,13 +16,33 @@ class Client:
     """
 
     def __init__(self, token: str, client: Any = None, timeout: float = 30.0):
-        self.client = client if client is not None else httpx.Client(timeout=timeout)
+        self._client = client
+        self._thread_local = threading.local()
+        self.timeout = timeout
         self.auth_header: str = f"Bearer {token}"
         self.headers: Dict[str, str] = {
             "Authorization": self.auth_header,
             "Content-Type": "application/json",
         }
 
+    @property
+    def client(self) -> Any:
+        """
+        Thread-safe access to the underlying HTTP client.
+        If a custom client was provided at initialization, it is returned.
+        Otherwise, a thread-local httpx.Client is created and returned.
+        """
+        if self._client is not None:
+            return self._client
+
+        if not hasattr(self._thread_local, "client"):
+            self._thread_local.client = httpx.Client(timeout=self.timeout)
+        return self._thread_local.client
+
+    @client.setter
+    def client(self, value: Any):
+        self._client = value
+
     def __enter__(self):
         """Enable use as a synchronous context manager."""
         return self
diff --git a/openapi_python_sdk/oauth_client.py b/openapi_python_sdk/oauth_client.py
index f6a418d..a3be9db 100644
--- a/openapi_python_sdk/oauth_client.py
+++ b/openapi_python_sdk/oauth_client.py
@@ -1,4 +1,5 @@
 import base64
+import threading
 from typing import Any, Dict, List
 
 import httpx
@@ -13,7 +14,9 @@ class OauthClient:
     """
 
     def __init__(self, username: str, apikey: str, test: bool = False, client: Any = None, timeout: float = 30.0):
-        self.client = client if client is not None else httpx.Client(timeout=timeout)
+        self._client = client
+        self._thread_local = threading.local()
+        self.timeout = timeout
         self.url: str = TEST_OAUTH_BASE_URL if test else OAUTH_BASE_URL
         self.auth_header: str = (
             "Basic " + base64.b64encode(f"{username}:{apikey}".encode("utf-8")).decode()
@@ -23,6 +26,23 @@ def __init__(self, username: str, apikey: str, test: bool = False, client: Any =
             "Content-Type": "application/json",
         }
 
+    @property
+    def client(self) -> Any:
+        """
+        Thread-safe access to the underlying HTTP client.
+        If a custom client was provided at initialization, it is returned.
+        Otherwise, a thread-local httpx.Client is created and returned.
+        """
+        if self._client is not None:
+            return self._client
+        if not hasattr(self._thread_local, "client"):
+            self._thread_local.client = httpx.Client(timeout=self.timeout)
+        return self._thread_local.client
+
+    @client.setter
+    def client(self, value: Any):
+        self._client = value
+
     def __enter__(self):
         """Enable use as a synchronous context manager."""
         return self
diff --git a/tests/test_thread_safety.py b/tests/test_thread_safety.py
new file mode 100644
index 0000000..5763084
--- /dev/null
+++ b/tests/test_thread_safety.py
@@ -0,0 +1,65 @@
+import threading
+import unittest
+
+import httpx
+
+from openapi_python_sdk import Client, OauthClient
+
+
+class TestThreadSafety(unittest.TestCase):
+    def test_oauth_client_thread_safety(self):
+        oauth = OauthClient(username="user", apikey="key")
+
+        clients = []
+        def get_client():
+            clients.append(oauth.client)
+
+        threads = [threading.Thread(target=get_client) for _ in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        # Each thread should have gotten a unique client instance
+        self.assertEqual(len(clients), 5)
+        self.assertEqual(len(set(id(c) for c in clients)), 5)
+
+    def test_client_thread_safety(self):
+        client = Client(token="tok")
+
+        clients = []
+        def get_client():
+            clients.append(client.client)
+
+        threads = [threading.Thread(target=get_client) for _ in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        # Each thread should have gotten a unique client instance
+        self.assertEqual(len(clients), 5)
+        self.assertEqual(len(set(id(c) for c in clients)), 5)
+
+    def test_shared_client_injection_still_works(self):
+        # If we explicitly pass a client, it SHOULD be shared (backward compatibility)
+        shared_engine = httpx.Client()
+        oauth = OauthClient(username="user", apikey="key", client=shared_engine)
+
+        clients = []
+        def get_client():
+            clients.append(oauth.client)
+
+        threads = [threading.Thread(target=get_client) for _ in range(5)]
+        for t in threads:
+            t.start()
+        for t in threads:
+            t.join()
+
+        # All threads should have the SAME instance because it was injected
+        self.assertEqual(len(clients), 5)
+        self.assertEqual(len(set(id(c) for c in clients)), 1)
+        self.assertEqual(id(clients[0]), id(shared_engine))
+
+if __name__ == "__main__":
+    unittest.main()