base_url

Base URL for API requests.

Resolution order (first match wins):

1. Explicit base_url kwarg.
2. Env var OPENAI_API_BASE (read by LangChain at init).
3. The LangSmith LLM gateway, when env var LANGSMITH_GATEWAY is set.
4. Env var OPENAI_BASE_URL (read by the underlying openai SDK client).