diff --git a/env.example b/env.example
index a45b158..552c40b 100644
--- a/env.example
+++ b/env.example
@@ -28,6 +28,9 @@ LLM_API_KEY=sk-...
 # Optional custom API base
 # BUB_API_BASE=https://openrouter.ai/api/v1
 
+# Use OpenAI Responses API (opt-in; keeps completions as default)
+# BUB_USE_RESPONSES=true
+
 # ---------------------------------------------------------------------------
 # Optional Ollama web tools override
 # ---------------------------------------------------------------------------
diff --git a/src/bub/config/settings.py b/src/bub/config/settings.py
index 504b885..a82a0f1 100644
--- a/src/bub/config/settings.py
+++ b/src/bub/config/settings.py
@@ -24,6 +24,7 @@ class Settings(BaseSettings):
     model: str = "openrouter:qwen/qwen3-coder-next"
     api_key: str | None = None
     api_base: str | None = None
+    use_responses: bool = False
     ollama_api_key: str | None = None
     ollama_api_base: str | None = None
     llm_api_key: str | None = Field(default=None, validation_alias="LLM_API_KEY")
diff --git a/src/bub/integrations/republic_client.py b/src/bub/integrations/republic_client.py
index 7d4efc9..1fda733 100644
--- a/src/bub/integrations/republic_client.py
+++ b/src/bub/integrations/republic_client.py
@@ -30,6 +30,7 @@ def build_llm(settings: Settings, store: FileTapeStore) -> LLM:
         settings.model,
         api_key=settings.resolved_api_key,
         api_base=settings.api_base,
+        use_responses=settings.use_responses,
         tape_store=store,
         context=default_tape_context(),
         client_args=client_args,