Use Claude with the OpenAI SDK: OpenAI-compatible endpoint, streaming, tools and limits

Code written for the OpenAI SDK can call Claude without a rewrite: point base_url at the gateway's /v1, use a gateway key and a Claude model ID. The endpoint accepts Chat Completions requests, streams in the same format and supports function calling. A few Claude features only exist in Anthropic's native format; the last section covers when to switch.

Endpoint facts

Python

pip install openai

import os
from openai import OpenAI

client = OpenAI(base_url="https://aiprimetech.io/v1", api_key=os.environ["AIPRIME_API_KEY"])

resp = client.chat.completions.create(
    model="claude-sonnet-5",
    max_tokens=1024,
    messages=[
        {"role": "system", "content": "You are a concise assistant."},
        {"role": "user", "content": "Explain idempotency keys in two sentences."},
    ],
)
print(resp.choices[0].message.content)
print(resp.usage)

base_url must end in /v1: the SDK appends /chat/completions to it. Without /v1 the request lands on the website and returns HTML; with /v1 twice it returns 404 page not found.

Node.js

import OpenAI from "openai";

const client = new OpenAI({ baseURL: "https://aiprimetech.io/v1", apiKey: process.env.AIPRIME_API_KEY });

const resp = await client.chat.completions.create({
  model: "claude-sonnet-5",
  max_tokens: 1024,
  messages: [{ role: "user", content: "Write a haiku about retries." }],
});
console.log(resp.choices[0].message.content);

Streaming

stream = client.chat.completions.create(
    model="claude-sonnet-5",
    max_tokens=2048,
    stream=True,
    stream_options={"include_usage": True},
    messages=[{"role": "user", "content": "Outline a zero-downtime migration."}],
)
for chunk in stream:
    if chunk.choices and chunk.choices[0].delta.content:
        print(chunk.choices[0].delta.content, end="", flush=True)
    if chunk.usage:
        print("\n", chunk.usage)

Stream long answers: a non-streaming request has to finish inside your client's timeout, a stream does not. include_usage adds a final chunk with token counts. More on why it matters in streaming LLM responses.

Function calling

tools = [{
    "type": "function",
    "function": {
        "name": "get_weather",
        "description": "Current weather for a city",
        "parameters": {
            "type": "object",
            "properties": {"city": {"type": "string"}},
            "required": ["city"],
        },
    },
}]

resp = client.chat.completions.create(
    model="claude-sonnet-5", max_tokens=512, tools=tools,
    messages=[{"role": "user", "content": "What is the weather in Paris?"}],
)
call = resp.choices[0].message.tool_calls[0]
print(call.function.name, call.function.arguments)   # get_weather {"city": "Paris"}

The reply comes back with finish_reason: "tool_calls" and OpenAI-style tool_calls. Run the function, append a tool message with the result and the matching tool_call_id, then call again, exactly as with OpenAI models.

Reasoning and thinking

reasoning_effort maps to Claude's effort setting and accepts low, medium, high, xhigh or max. The value none is rejected. When the model thinks, its reasoning arrives in a separate reasoning_content field next to content, so code that reads message.content keeps working unchanged.

resp = client.chat.completions.create(
    model="claude-opus-5-5", max_tokens=4096, reasoning_effort="high",
    messages=[{"role": "user", "content": "Find the bug in this function: ..."}],
)

Models

Use these IDs exactly. Old dated IDs such as claude-3-5-sonnet-20241022 still appear in some model lists but are not served and return a model-not-supported error.

When to use the native Anthropic API instead

The OpenAI format covers chat, streaming, tools and images. Use Anthropic's own Messages format, at the same gateway, when you need explicit prompt-cache breakpoints, thinking blocks you pass back between turns, PDF documents or citations. The Anthropic Python SDK guide and the Vercel AI SDK guide cover that route.

Troubleshooting

Frequently asked questions

AI Prime Tech is an independent API gateway. It is not affiliated with, endorsed by, or a reseller of Anthropic. Claude and related model names are trademarks of their respective owners.