I’m working with LangChain and I’m confused about which environment variable to set for the API key. In older tutorials, I found references to using LANGCHAIN_API_KEY, but the latest documents indicate that LANGSMITH_API_KEY is the new standard. Could someone clarify the difference between these two API key variables? Should I use the LANGSMITH_API_KEY for my current projects, or is there a reason to use both? Any insights would be helpful to ensure I’m following the right practices.
Both keys work, but use LANGSMITH_API_KEY for new projects. I learned this while debugging auth issues last quarter - LANGCHAIN_API_KEY just gets redirected to LangSmith anyway, which adds overhead. They split things up so LangSmith handles observability while LangChain stays the main framework. LANGSMITH_API_KEY connects directly without the redirect, so requests run faster. I saw about 50ms better trace initialization after switching. The docs mention both keys for backwards compatibility, but the infrastructure clearly prefers the LangSmith one.
Everyone’s right about LANGSMITH_API_KEY, but here’s what I learned migrating dozens of microservices at work.
The real pain hits when you’ve got multiple environments and teams using different variables. I spent weeks manually updating config files across dev, staging, and prod.
So I built an automation workflow that scans all our repos for old LANGCHAIN_API_KEY references and swaps them to LANGSMITH_API_KEY. It also updates CI/CD pipelines and deployment scripts.
Runs weekly and catches any new code still using the deprecated variable. Saves hours of manual work and kills those “why isn’t my tracing working” tickets.
Set up something similar to handle this migration automatically across your projects. Way better than manual find and replace every time.
Had the exact same issue when I first set up LangSmith on production. The naming change totally threw me off.
Yeah, use LANGSMITH_API_KEY. The old LANGCHAIN_API_KEY was confusing - you couldn’t tell what service you were actually connecting to.
Once LangSmith split off, they needed separate API boundaries. Makes sense - you don’t want your tracing service using the same auth as your main framework.
I’ve watched teams struggle with this because they’re following old tutorials. This video shows the whole setup and which variables to actually use:
Tracing works great once it’s configured properly. Just keep your environment variables consistent across deployments.
yeah, def use LANGSMITH_API_KEY! i made that mistake last month and wasted a ton of time figuring out y my traceing wasn’t working. the langchain one is legacy now - switch to save urself the headache!
I switched from LANGCHAIN_API_KEY to LANGSMITH_API_KEY about six months ago during a project upgrade. LangSmith split off as its own service for observability and evaluation, so it needed its own key. LANGSMITH_API_KEY connects you directly to LangSmith’s tracing and monitoring - the old variable was too generic and you couldn’t tell which service you were hitting. I’d make the switch now instead of putting it off. Took me maybe ten minutes to update my environment files and configs. The new naming’s way clearer, especially when you’re juggling multiple tools from the LangChain ecosystem.
Use LANGSMITH_API_KEY now.
LANGCHAIN_API_KEY got deprecated when they split LangChain and LangSmith apart. LangSmith handles tracing, monitoring, and debugging.
I ran into this same thing about 8 months back when updating projects. The old key still works but you’ll get warnings and it might break later.
Just set LANGSMITH_API_KEY in your environment. You only need both if you’re stuck with legacy code that hasn’t been updated.
They split because LangSmith’s its own platform now, so it needs separate API auth from LangChain.