Skip to main content


This page covers how to use the Modal ecosystem to run LangChain custom LLMs. It is broken into two parts:

  1. Modal installation and web endpoint deployment
  2. Using deployed web endpoint with LLM wrapper class.

Installation and Setup​

  • Install with pip install modal
  • Run modal token new

Define your Modal Functions and Webhooks​

You must include a prompt. There is a rigid response structure:

class Item(BaseModel):
prompt: str

def get_text(item: Item):
return {"prompt":}

The following is an example with the GPT2 model:

from pydantic import BaseModel

import modal

CACHE_PATH = "/root/model_cache"

class Item(BaseModel):
prompt: str

stub = modal.Stub(name="example-get-started-with-langchain")

def download_model():
from transformers import GPT2Tokenizer, GPT2LMHeadModel
tokenizer = GPT2Tokenizer.from_pretrained('gpt2')
model = GPT2LMHeadModel.from_pretrained('gpt2')

# Define a container image for the LLM function below, which
# downloads and stores the GPT-2 model.
image = modal.Image.debian_slim().pip_install(
"tokenizers", "transformers", "torch", "accelerate"

def run_gpt2(text: str):
from transformers import GPT2Tokenizer, GPT2LMHeadModel
tokenizer = GPT2Tokenizer.from_pretrained(CACHE_PATH)
model = GPT2LMHeadModel.from_pretrained(CACHE_PATH)
encoded_input = tokenizer(text, return_tensors='pt').input_ids
output = model.generate(encoded_input, max_length=50, do_sample=True)
return tokenizer.decode(output[0], skip_special_tokens=True)

def get_text(item: Item):
return {"prompt":}

Deploy the web endpoint​

Deploy the web endpoint to Modal cloud with the modal deploy CLI command. Your web endpoint will acquire a persistent URL under the domain.

LLM wrapper around Modal web endpoint​

The Modal LLM wrapper class which will accept your deployed web endpoint's URL.

from langchain_community.llms import Modal

endpoint_url = "" # REPLACE ME with your deployed Modal web endpoint's URL

llm = Modal(endpoint_url=endpoint_url)
llm_chain = LLMChain(prompt=prompt, llm=llm)

question = "What NFL team won the Super Bowl in the year Justin Beiber was born?"
API Reference:Modal

Was this page helpful?

You can leave detailed feedback on GitHub.