LangChain vs LangGraph

from langchain_openai import ChatOpenAI
from langchain_core.prompts import ChatPromptTemplate

llm = ChatOpenAI(model="gpt-4o")

prompt = ChatPromptTemplate.from_messages([
    ("system", "You are a helpful assistant."),
    ("user", "{input}"),
])

chain = prompt | llm
response = chain.invoke({"input": "Hello!"})
print(response.content)

import { StateGraph, END } from '@langchain/langgraph';

const workflow = new StateGraph({ channels: { messages: { value: (x, y) => x.concat(y) } } });

workflow.addNode('agent', async (state) => {
  const response = await llm.invoke(state.messages);
  return { messages: [response] };
});

workflow.setEntryPoint('agent');
workflow.addEdge('agent', END);

const app = workflow.compile();
const result = await app.invoke({ messages: [{ role: 'user', content: 'Hello' }] });