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The Modal cloud platform provides convenient, on-demand access to serverless cloud compute from Python scripts on your local computer. Use modal to run your own custom LLM models instead of depending on LLM APIs. This example goes over how to use LangChain to interact with a modal HTTPS web endpoint. Question-answering with LangChain is another example of how to use LangChain alonside Modal. In that example, Modal runs the LangChain application end-to-end and uses OpenAI as its LLM API. 
pip install -qU  modal

# Register an account with Modal and get a new token.

!modal token new

Launching login page in your browser window...
If this is not showing up, please copy this URL into your web browser manually:
https://modal.com/token-flow/tf-Dzm3Y01234mqmm1234Vcu3
The langchain.llms.modal.Modal integration class requires that you deploy a Modal application with a web endpoint that complies with the following JSON interface:
  1. The LLM prompt is accepted as a str value under the key "prompt"
  2. The LLM response returned as a str value under the key "prompt"
Example request JSON: 
{
    "prompt": "Identify yourself, bot!",
    "extra": "args are allowed",
}
Example response JSON: 
{
    "prompt": "This is the LLM speaking",
}
An example ‘dummy’ Modal web endpoint function fulfilling this interface would be 
...
...

class Request(BaseModel):
    prompt: str

@stub.function()
@modal.web_endpoint(method="POST")
def web(request: Request):
    _ = request  # ignore input
    return {"prompt": "hello world"}
Once you have a deployed Modal web endpoint, you can pass its URL into the langchain.llms.modal.Modal LLM class. This class can then function as a building block in your chain. 
from langchain_classic.chains import LLMChain
from langchain_community.llms import Modal
from langchain_core.prompts import PromptTemplate

template = """Question: {question}

Answer: Let's think step by step."""

prompt = PromptTemplate.from_template(template)

endpoint_url = "https://ecorp--custom-llm-endpoint.modal.run"  # 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?"

llm_chain.run(question)
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