diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0681e9e24..8f2eef7c2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 6.4.1 - 2025-08-06
+
+- fix: Always pass project API key in `remote_config` requests for deterministic project routing
+
 # 6.4.0 - 2025-08-05
 
 - feat: support Vertex AI for Gemini
diff --git a/posthog/client.py b/posthog/client.py
index 143d4630b..323e81bee 100644
--- a/posthog/client.py
+++ b/posthog/client.py
@@ -1644,6 +1644,7 @@ def get_remote_config_payload(self, key: str):
         try:
             return remote_config(
                 self.personal_api_key,
+                self.api_key,
                 self.host,
                 key,
                 timeout=self.feature_flags_request_timeout_seconds,
diff --git a/posthog/request.py b/posthog/request.py
index 8680c83e5..2b97872f4 100644
--- a/posthog/request.py
+++ b/posthog/request.py
@@ -132,12 +132,16 @@ def flags(
 
 
 def remote_config(
-    personal_api_key: str, host: Optional[str] = None, key: str = "", timeout: int = 15
+    personal_api_key: str,
+    project_api_key: str,
+    host: Optional[str] = None,
+    key: str = "",
+    timeout: int = 15,
 ) -> Any:
     """Get remote config flag value from remote_config API endpoint"""
     return get(
         personal_api_key,
-        f"/api/projects/@current/feature_flags/{key}/remote_config/",
+        f"/api/projects/@current/feature_flags/{key}/remote_config?token={project_api_key}",
         host,
         timeout,
     )
diff --git a/posthog/test/test_client.py b/posthog/test/test_client.py
index c9507e054..5e9328e2e 100644
--- a/posthog/test/test_client.py
+++ b/posthog/test/test_client.py
@@ -2,13 +2,13 @@
 import unittest
 from datetime import datetime
 from uuid import uuid4
-from posthog.contexts import get_context_session_id, set_context_session, new_context
 
 import mock
 import six
 from parameterized import parameterized
 
 from posthog.client import Client
+from posthog.contexts import get_context_session_id, new_context, set_context_session
 from posthog.request import APIError
 from posthog.test.test_utils import FAKE_TEST_API_KEY
 from posthog.types import FeatureFlag, LegacyFlagMetadata
@@ -2057,7 +2057,7 @@ def test_set_context_session_with_page_explicit_properties(self):
 
     def test_set_context_session_override_in_capture(self):
         """Test that explicit session ID overrides context session ID in capture"""
-        from posthog.contexts import set_context_session, new_context
+        from posthog.contexts import new_context, set_context_session
 
         with mock.patch("posthog.client.batch_post") as mock_post:
             client = Client(FAKE_TEST_API_KEY, on_error=self.set_fail, sync_mode=True)
@@ -2158,6 +2158,7 @@ def test_get_remote_config_payload_works_without_poller(self, patch_remote_confi
         self.assertEqual(result, {"test": "payload"})
         patch_remote_config.assert_called_once_with(
             "test-personal-key",
+            FAKE_TEST_API_KEY,
             client.host,
             "test-flag",
             timeout=client.feature_flags_request_timeout_seconds,
@@ -2282,9 +2283,7 @@ def test_get_feature_flag_result_with_empty_string_payload(self, patch_batch_pos
                             }
                         ]
                     },
-                    "payloads": {
-                        "empty-variant": ""  # Empty string payload
-                    },
+                    "payloads": {"empty-variant": ""},  # Empty string payload
                 },
             }
         ]
diff --git a/posthog/version.py b/posthog/version.py
index d17cba7e3..d66a32095 100644
--- a/posthog/version.py
+++ b/posthog/version.py
@@ -1,4 +1,4 @@
-VERSION = "6.4.0"
+VERSION = "6.4.1"
 
 if __name__ == "__main__":
     print(VERSION, end="")  # noqa: T201
diff --git a/remote_config_example.py b/remote_config_example.py
new file mode 100644
index 000000000..ec5506fea
--- /dev/null
+++ b/remote_config_example.py
@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+"""
+Simple test script for PostHog remote config endpoint.
+"""
+
+import posthog
+
+# Initialize PostHog client
+posthog.api_key = "phc_..."
+posthog.personal_api_key = "phs_..."  # or "phx_..."
+posthog.host = "http://localhost:8000"  # or "https://us.posthog.com"
+posthog.debug = True
+
+
+def test_remote_config():
+    """Test remote config payload retrieval."""
+    print("Testing remote config endpoint...")
+
+    # Test feature flag key - replace with an actual flag key from your project
+    flag_key = "unencrypted-remote-config-setting"
+
+    try:
+        # Get remote config payload
+        payload = posthog.get_remote_config_payload(flag_key)
+        print(f"✅ Success! Remote config payload for '{flag_key}': {payload}")
+
+    except Exception as e:
+        print(f"❌ Error getting remote config: {e}")
+
+
+if __name__ == "__main__":
+    test_remote_config()