## The problem
Issue langchain-ai/langsmith-sdk#666 (closed, 11 comments): 401 Unauthorized when following langsmith tracing instructions. Set LANGCHAIN_TRACING_V2=true, LANGCHAIN_ENDPOINT='https://api.smith.langchain.com', LANGCHAIN_API_KEY. Still getting auth errors.
## What to do
[sahellebusch (reporter)]: If you get 401s after following the tracing setup docs, check which key you pasted: it must be the regular LangSmith API key (LANGCHAIN_API_KEY), not the LangChain Hub key. The reporter was using the Hub key by mistake and everything worked once swapped.