If you're building with LangChain or LlamaIndex, you probably have OpenAI's API key hardcoded somewhere and an eye on your usage bill. You can route the same code to open-source models — Nemotron 120B, Gemma 4, DeepSeek V4, Kimi K3, and more — for a fraction of the per-token cost, with two environment variables and no code changes. One ifu_ key reaches both open NVIDIA NIM endpoints and every major premium provider at the provider's published rate (zero markup).

LangChain

LangChain's ChatOpenAI accepts a custom base_url. Point it at InferAll:

from langchain_openai import ChatOpenAI

# Before: ChatOpenAI(model="gpt-4o", openai_api_key="sk-...")
# After: open-source model at NIM rate, same code
llm = ChatOpenAI(
    model="nvidia/nemotron-3-super-120b-a12b",  # NVIDIA NIM open model
    base_url="https://api.inferall.ai/v1",
    api_key="ifu_your_key_here",  # get one at inferall.ai/keys
)

response = llm.invoke("What are the SOLID principles in software design?")
print(response.content)

Or use environment variables so your code stays unchanged:

export OPENAI_BASE_URL=https://api.inferall.ai/v1
export OPENAI_API_KEY=ifu_your_key_here

from langchain_openai import ChatOpenAI

# No changes to your existing code needed
llm = ChatOpenAI(model="nvidia/nemotron-3-super-120b-a12b")

LangChain with chains and agents

from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser

llm = ChatOpenAI(
    model="nvidia/nemotron-3-super-120b-a12b",
    base_url="https://api.inferall.ai/v1",
    api_key="ifu_your_key_here",
)

# Standard LangChain chains work unchanged
prompt = ChatPromptTemplate.from_messages([
    ("system", "You are a helpful code assistant."),
    ("user", "{question}")
])

chain = prompt | llm | StrOutputParser()
result = chain.invoke({"question": "How do I implement a binary search tree in Python?"})
print(result)

LangChain with streaming

for chunk in llm.stream("Explain gradient descent step by step."):
    print(chunk.content, end="", flush=True)

LlamaIndex

LlamaIndex also uses the OpenAI client under the hood:

from llama_index.llms.openai import OpenAI
from llama_index.core import Settings

# Set InferAll as the LLM backend
Settings.llm = OpenAI(
    model="nvidia/nemotron-3-super-120b-a12b",
    api_base="https://api.inferall.ai/v1",
    api_key="ifu_your_key_here",
)

# Now use LlamaIndex normally — routes through NIM open models at NIM rate
from llama_index.core import VectorStoreIndex, SimpleDirectoryReader

documents = SimpleDirectoryReader("./data").load_data()
index = VectorStoreIndex.from_documents(documents)
query_engine = index.as_query_engine()
response = query_engine.query("What is this document about?")
print(response)

Which open model for LangChain development?

Model	Use case
`nvidia/nemotron-3-super-120b-a12b`	Complex reasoning, longer context
`google/gemma-4-31b-it`	General purpose, instruction following
`poolside/laguna-xs-2.1`	Code generation and review
`deepseek-ai/deepseek-v4-flash-0731`	Fast code tasks
`moonshotai/kimi-k3`	Structured outputs and agent steps

All on NVIDIA NIM at our open-model rate — the cheapest tier in the gateway.

Switch to premium models when production demands it

# Development / high-volume inner loop: open model on NIM
llm = ChatOpenAI(model="nvidia/nemotron-3-super-120b-a12b", ...)

# Production hard task: swap to Claude Sonnet at Anthropic's published rate (zero markup)
# Just change the model string — same base_url, same key
llm = ChatOpenAI(model="anthropic/claude-sonnet-4-6", ...)  # or openai/gpt-4o

Get started

Sign up at inferall.ai/keys and fund a key with the $5 starter pack — that $5 becomes usage credit you can spend on any model (open or premium) at the provider's published rate with zero markup. See the LLM API aggregator overview for full details on supported providers and models.

Use LangChain with open-source LLMs — one API key for everything