diff --git a/.env.template b/.env.template
index 5d3d862..84167fa 100644
--- a/.env.template
+++ b/.env.template
@@ -1,5 +1,6 @@
 # To set API keys, copy this as .env and fill in the values
 # API keys are required to rewrite the VCR cassettes for the tests
 ANTHROPIC_API_KEY="anthropic_api_key"
+GEMINI_API_KEY="gemini_api_key"
 MISTRAL_API_KEY="mistral_api_key"
 OPENAI_API_KEY="openai_api_key"
diff --git a/pyproject.toml b/pyproject.toml
index 4326802..da3d8eb 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -91,6 +91,7 @@ markers = [
     "litellm_openai: Tests that query the OpenAI API via litellm. Requires the OPENAI_API_KEY environment variable to be set.",
     "mistral: Tests that query the Mistral API (via openai). Requires the MISTRAL_API_KEY environment variable to be set.",
     "openai: Tests that query the OpenAI API. Requires the OPENAI_API_KEY environment variable to be set.",
+    "openai_gemini: Tests that query the Gemini API via openai. Requires the GEMINI_API_KEY environment variable to be set.",
     "openai_ollama: Tests that query Ollama via openai. Requires ollama to be installed and running on localhost:11434.",
 ]
 
diff --git a/src/magentic/chat_model/openai_chat_model.py b/src/magentic/chat_model/openai_chat_model.py
index 468fd30..35bac9a 100644
--- a/src/magentic/chat_model/openai_chat_model.py
+++ b/src/magentic/chat_model/openai_chat_model.py
@@ -350,7 +350,10 @@ def update(self, item: ChatCompletionChunk) -> None:
                 tool_call_chunk.index = self._current_tool_call_index
         self._chat_completion_stream_state.handle_chunk(item)
         if item.usage:
-            assert not self.usage_ref
+            # Only keep the last usage
+            # Gemini openai-compatible API includes usage in all streamed chunks
+            # but OpenAI only includes this in the last chunk
+            self.usage_ref.clear()
             self.usage_ref.append(
                 Usage(
                     input_tokens=item.usage.prompt_tokens,
diff --git a/tests/chat_model/test_openai_chat_model_gemini.py b/tests/chat_model/test_openai_chat_model_gemini.py
new file mode 100644
index 0000000..c2ab7b0
--- /dev/null
+++ b/tests/chat_model/test_openai_chat_model_gemini.py
@@ -0,0 +1,52 @@
+import os
+
+import pytest
+
+from magentic.chat_model.message import UserMessage
+from magentic.chat_model.openai_chat_model import OpenaiChatModel
+
+
+@pytest.mark.parametrize(
+    ("prompt", "output_types", "expected_output_type"),
+    [
+        ("Say hello!", [str], str),
+        ("Return True.", [bool], bool),
+        ("Return [1, 2, 3, 4, 5]", [list[int]], list),
+        ("Return a list of fruit", [list[str]], list),
+    ],
+)
+@pytest.mark.openai_gemini
+def test_openai_chat_model_complete_gemini(prompt, output_types, expected_output_type):
+    chat_model = OpenaiChatModel(
+        "gemini-1.5-flash",
+        api_key=os.environ["GEMINI_API_KEY"],
+        base_url="https://generativelanguage.googleapis.com/v1beta/openai/",
+    )
+    message = chat_model.complete(
+        messages=[UserMessage(prompt)], output_types=output_types
+    )
+    assert isinstance(message.content, expected_output_type)
+
+
+@pytest.mark.parametrize(
+    ("prompt", "output_types", "expected_output_type"),
+    [
+        ("Say hello!", [str], str),
+        ("Return True.", [bool], bool),
+        ("Return [1, 2, 3, 4, 5]", [list[int]], list),
+        ("Return a list of fruit", [list[str]], list),
+    ],
+)
+@pytest.mark.openai_gemini
+async def test_openai_chat_model_acomplete_gemini(
+    prompt, output_types, expected_output_type
+):
+    chat_model = OpenaiChatModel(
+        "gemini-1.5-flash",
+        api_key=os.environ["GEMINI_API_KEY"],
+        base_url="https://generativelanguage.googleapis.com/v1beta/openai/",
+    )
+    message = await chat_model.acomplete(
+        messages=[UserMessage(prompt)], output_types=output_types
+    )
+    assert isinstance(message.content, expected_output_type)
diff --git a/tests/conftest.py b/tests/conftest.py
index 060f782..c4205e5 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -75,6 +75,7 @@ def pytest_collection_modifyitems(
         "litellm_openai",
         "mistral",
         "openai",
+        "openai_gemini",
         "openai_ollama",
     ]
     for item in items: