Gateway Key from Env Var

What it does

A new env var LANGCHAIN_LANGCHAIN_GATEWAY_API_KEY was introduced across langchain-anthropic, langchain-fireworks, and langchain-openai (PR #38742). Instead of passing a langchain_gateway_api_key argument explicitly when initializing a model client, you set it once as an env var and every LangChain integration talking to LangSmith Gateway picks it up automatically.

Why it matters

Production pipelines often initialize many model clients (OpenAI, Anthropic, Fireworks) sharing the same LangSmith Gateway endpoint and credentials. Before, you had to pass langchain_gateway_api_key="..." to every .bind() or .with_structured_output() call — error-prone and verbose. A single process-level export covers them all. This shines in cron jobs, Docker containers, and serverless functions where secrets are injected via environment variables.

Example

$ import os
os.environ["LANGCHAIN_LANGCHAIN_GATEWAY_API_KEY"] = "sk-..."
from langchain_openai import ChatOpenAI
llm = ChatOpenAI(model="gpt-4o")
print(llm.invoke("What is LangSmith?").content)

LangSmith is a platform for debugging, testing, and monitoring
LangChain applications. It provides tracing, evaluation, and
dataset management capabilities to help you improve your LLM
pipelines over time.

Common flags

LANGCHAIN_LANGCHAIN_GATEWAY_API_KEY

Env var supplying the gateway API key to all integrations

langchain_gateway_api_key

Explicit constructor arg now optional when the env var is set

with_structured_output()

Structured-output calls that inherit the gateway key