Reasoning · framework

Use Claude 3.5 Sonnet (Thinking) with LangChain

Updated 2026-05-21 · By XALEN

How to use Claude 3.5 Sonnet (Thinking) (Reasoning, ~500B) with LangChain. Install, authenticate, and make your first API call in minutes. Working code example included.

Model

Claude 3.5 Sonnet (Thinking)

~500B · 200K context · $0.03 input

Framework

LangChain

framework · pip install langchain-openai

1. Install

pip install langchain-openai

2. Code

from langchain_openai import ChatOpenAI

llm = ChatOpenAI(
    model="claude-3-5-sonnet-thinking",
    openai_api_key="xln_test_YOUR_KEY",
    openai_api_base="https://api.xalen.io/v1"
)

response = llm.invoke("What is Claude 3.5 Sonnet (Thinking)?")
print(response.content)

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Last updated: 2026-05-21