LangChain API key

The LangChain API key is an environment variable that grants your LangChain application permission to call a hosted large language model (LLM) provider — OpenAI, Anthropic, Gemini, Azure OpenAI — or a vector service like Pinecone. You export the key in a wrapper or .env file — export OPENAI_API_KEY=sk-… — before running Python; LangChain wrappers automatically pick it up via os.getenv. Each provider expects a specific variable name (OPENAI_API_KEY, ANTHROPIC_API_KEY, GOOGLE_API_KEY), and you can load multiple keys side by side in hot-swappable models in router chains. Best practice is to store keys in cloud secret managers (AWS Secrets Manager, Azure Key Vault) or CI repositories rather than hard-coding them, and callbacks obfuscate keys in logs to prevent leaks. Rotate keys regularly and set project quotas to avoid uncontrolled spending. In short, the LangChain API key is your ticket to the external power of LLM – treat it as a trade secret, not an afterthought configuration.