diff --git a/artemis/llm/router.py b/artemis/llm/router.py
index f2e6b42b6..a56cc34d9 100644
--- a/artemis/llm/router.py
+++ b/artemis/llm/router.py
@@ -22,6 +22,7 @@
 from enum import StrEnum
 import hashlib
 import os
+import re
 from typing import Any
 
 from langchain_core.language_models.chat_models import BaseChatModel
@@ -383,6 +384,11 @@ def create_model(cls, endpoint: ModelEndpoint) -> BaseChatModel:
             }
             if endpoint.reasoning_effort:
                 kwargs["reasoning_effort"] = endpoint.reasoning_effort
+            # Some OpenAI-compatible endpoints serve function tools only on the Responses API (e.g. GPT-6.x on
+            # Amazon Bedrock). Opt in per model with ARTEMIS_OPENAI_RESPONSES_API, a regex on the model name.
+            responses_models = os.environ.get("ARTEMIS_OPENAI_RESPONSES_API")
+            if responses_models and re.search(responses_models, endpoint.model_name or ""):
+                kwargs["use_responses_api"] = True
             return ChatOpenAI(**{k: v for k, v in kwargs.items() if v is not None})
 
         else:
diff --git a/tests/unit/test_model_factory_responses_api.py b/tests/unit/test_model_factory_responses_api.py
new file mode 100644
index 000000000..9ca424ded
--- /dev/null
+++ b/tests/unit/test_model_factory_responses_api.py
@@ -0,0 +1,42 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""ARTEMIS_OPENAI_RESPONSES_API opts matching OpenAI-compatible models into the Responses API."""
+
+from unittest.mock import patch
+
+from artemis.llm.router import ModelEndpoint, ModelFactory, ModelProvider
+
+
+def _kwargs(model_name: str) -> dict:
+    with patch("langchain_openai.ChatOpenAI") as chat_openai:
+        ModelFactory.create_model(
+            ModelEndpoint(provider=ModelProvider.CUSTOM, model_name=model_name)
+        )
+    return chat_openai.call_args.kwargs
+
+
+def test_matching_model_uses_the_responses_api(monkeypatch):
+    monkeypatch.setenv("ARTEMIS_OPENAI_RESPONSES_API", r"openai\.gpt-6")
+    assert _kwargs("global.openai.gpt-6.1-sol")["use_responses_api"] is True
+
+
+def test_non_matching_model_keeps_chat_completions(monkeypatch):
+    monkeypatch.setenv("ARTEMIS_OPENAI_RESPONSES_API", r"openai\.gpt-6")
+    assert "use_responses_api" not in _kwargs("qwen.qwen3-vl-235b-a22b")
+
+
+def test_unset_opt_in_changes_nothing(monkeypatch):
+    monkeypatch.delenv("ARTEMIS_OPENAI_RESPONSES_API", raising=False)
+    assert "use_responses_api" not in _kwargs("global.openai.gpt-6.1-sol")