diff --git a/.env.sample b/.env.sample
index 6fee2d2..e770b53 100644
--- a/.env.sample
+++ b/.env.sample
@@ -25,7 +25,7 @@ AZURE_TENANT_ID=
 AZURE_OPENAI_KEY=
 # Needed for OpenAI.com:
 OPENAICOM_KEY=YOUR-OPENAI-API-KEY
-OPENAICOM_CHAT_MODEL=gpt-3.5-turbo
+OPENAICOM_CHAT_MODEL=gpt-5.4
 OPENAICOM_EMBED_MODEL=text-embedding-3-large
 OPENAICOM_EMBED_DIMENSIONS=1024
 OPENAICOM_EMBEDDING_COLUMN=embedding_3l
diff --git a/infra/main.bicep b/infra/main.bicep
index ea80075..b465a05 100644
--- a/infra/main.bicep
+++ b/infra/main.bicep
@@ -354,7 +354,7 @@ var webAppEnv = union(azureOpenAIKeyEnv, openAIComKeyEnv, [
   }
   {
     name: 'OPENAICOM_CHAT_MODEL'
-    value: openAIChatHost == 'openaicom' ? 'gpt-3.5-turbo' : ''
+    value: openAIChatHost == 'openaicom' ? 'gpt-5.4' : ''
   }
   {
     name: 'OPENAI_EMBED_HOST'
diff --git a/src/backend/fastapi_app/dependencies.py b/src/backend/fastapi_app/dependencies.py
index fdd7063..575b4a3 100644
--- a/src/backend/fastapi_app/dependencies.py
+++ b/src/backend/fastapi_app/dependencies.py
@@ -65,7 +65,7 @@ async def common_parameters():
         openai_embed_model = os.getenv("OLLAMA_EMBED_MODEL") or "nomic-embed-text"
     else:
         openai_chat_deployment = None
-        openai_chat_model = os.getenv("OPENAICOM_CHAT_MODEL") or "gpt-3.5-turbo"
+        openai_chat_model = os.getenv("OPENAICOM_CHAT_MODEL") or "gpt-5.4"
     return FastAPIAppContext(
         openai_chat_model=openai_chat_model,
         openai_embed_model=openai_embed_model,
diff --git a/tests/conftest.py b/tests/conftest.py
index 4400685..6820784 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -97,7 +97,7 @@ def mock_session_env_openai(monkeypatch_session):
         monkeypatch_session.setenv("OPENAI_CHAT_HOST", "openai")
         monkeypatch_session.setenv("OPENAI_EMBED_HOST", "openai")
         monkeypatch_session.setenv("OPENAICOM_KEY", "fakekey")
-        monkeypatch_session.setenv("OPENAICOM_CHAT_MODEL", "gpt-3.5-turbo")
+        monkeypatch_session.setenv("OPENAICOM_CHAT_MODEL", "gpt-5.4")
         monkeypatch_session.setenv("OPENAICOM_EMBED_MODEL", "text-embedding-3-large")
         monkeypatch_session.setenv("OPENAICOM_EMBED_DIMENSIONS", "1024")
         monkeypatch_session.setenv("OPENAICOM_EMBEDDING_COLUMN", "embedding_3l")
diff --git a/tests/test_dependencies.py b/tests/test_dependencies.py
index 1c4d90d..135b799 100644
--- a/tests/test_dependencies.py
+++ b/tests/test_dependencies.py
@@ -26,13 +26,20 @@ async def test_get_common_parameters_ollama(mock_session_env_ollama):
 @pytest.mark.asyncio
 async def test_get_common_parameters_openai(mock_session_env_openai):
     result = await common_parameters()
-    assert result.openai_chat_model == "gpt-3.5-turbo"
+    assert result.openai_chat_model == "gpt-5.4"
     assert result.openai_embed_model == "text-embedding-3-large"
     assert result.openai_embed_dimensions == 1024
     assert result.openai_chat_deployment is None
     assert result.openai_embed_deployment is None
 
 
+@pytest.mark.asyncio
+async def test_get_common_parameters_openai_default_chat_model(mock_session_env_openai, monkeypatch):
+    monkeypatch.delenv("OPENAICOM_CHAT_MODEL", raising=False)
+    result = await common_parameters()
+    assert result.openai_chat_model == "gpt-5.4"
+
+
 @pytest.mark.asyncio
 async def test_get_azure_credential(mock_session_env, mock_azure_credential):
     result = await get_azure_credential()