Migrate from the OpenAI API to Claude: what changes in code

To move from OpenAI to Claude, you can keep the OpenAI SDK and change three settings: the base URL https://api.5abeer.ai/v1, a 5abeer key for Claude models, and a Claude model id such as claude-sonnet-5.5. For Claude's own settings, such as prompt caching, switch to the Anthropic SDK at https://api.5abeer.ai. Both routes take the same key.

What changes when you move from OpenAI to Claude?#

5abeer is OpenAI-compatible: change the base URL and keep your code. Three settings change:

Then pick a route: keep the OpenAI SDK, the smallest change, or move to the Anthropic SDK, which reaches every Claude setting. How an SDK builds each address is in What is a base URL.

Route 1: keep the OpenAI SDK#

Put your key in the KHABEER_API_KEY environment variable, then change the client and the model id:

import os
from openai import OpenAI

client = OpenAI(
    base_url="https://api.5abeer.ai/v1",
    api_key=os.environ["KHABEER_API_KEY"],
)

response = client.chat.completions.create(
    model="claude-sonnet-5.5",
    messages=[
        {"role": "system", "content": "Answer in two sentences."},
        {"role": "user", "content": "What is a context window?"},
    ],
)

print(response.choices[0].message.content)

In the Node.js library the option is called baseURL:

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.5abeer.ai/v1",
  apiKey: process.env.KHABEER_API_KEY,
});

const response = await client.chat.completions.create({
  model: "claude-sonnet-5.5",
  messages: [{ role: "user", content: "What is a context window?" }],
});

console.log(response.choices[0].message.content);

Both libraries also read OPENAI_BASE_URL and OPENAI_API_KEY when you don't pass them in code, so a project can switch by setting two variables and changing the model id. Code that calls client.responses.create keeps working too: Claude models are served on Responses as well.

Which Claude model should I pick?#

The Claude models you can call now:

Start with claude-sonnet-5.5, the default on 5abeer, and try claude-opus-5.5 or claude-fable-5.1 on your hardest prompts; Which Claude model to use compares them. Copy each id as our catalog writes it, with a dot in the version, even where Anthropic's docs use a hyphen. client.models.list() returns the models your key can use, as in List models.

Route 2: move to the Anthropic SDK#

Claude's own settings, such as cache_control, thinking settings and output_config, live in Anthropic's format. 5abeer is compatible with the Anthropic Messages API, so the official SDK works with it. Install it with pip install anthropic:

import os
from anthropic import Anthropic

client = Anthropic(
    base_url="https://api.5abeer.ai",
    api_key=os.environ["KHABEER_API_KEY"],
)

message = client.messages.create(
    model="claude-sonnet-5.5",
    max_tokens=4096,
    system="Answer in two sentences.",
    messages=[{"role": "user", "content": "What is a context window?"}],
)

print("".join(block.text for block in message.content if block.type == "text"))

Four things differ from the OpenAI code:

• The base URL has no /v1. The Anthropic SDK adds the path itself.
• max_tokens is required, and the instructions go in the top-level system field.
• Thinking is on by default on Claude 5 models. Anthropic counts thinking tokens toward max_tokens and bills them as output, so leave room: these samples use 4096.
• The reply is a list of blocks, and a thinking block can come before the text. Read the text blocks, not the first block.

The SDK also reads ANTHROPIC_BASE_URL and ANTHROPIC_API_KEY from the environment, as in Base URLs.

How do Chat Completions and Messages differ?#

The same conversation sits in different fields. Moving to Messages means renaming these:

Each field is in the Messages reference, and the same tool in each format is in Tool calling.

Which OpenAI options work with Claude on 5abeer?#

From our Chat Completions reference. An ignored option causes no error; it just has no effect.

Anthropic's docs, checked on 2026-11-03, add two limits. On Claude 4.7 and later models, a non-default temperature or top_p returns a 400 error. On claude-opus-5.5, claude-sonnet-5.5 and claude-fable-5.1, so does a forced tool call through tool_choice. Leave the sampling settings out, keep tool_choice at auto, and name the tool you want in the prompt.

How do I get JSON from Claude?#

response_format has no effect with Claude models on our Chat Completions, so ask for JSON through a tool. With the Anthropic SDK, describe a tool whose input_schema holds the fields you want, and read them from the tool_use block:

tools = [{
    "name": "save_city",
    "description": "Save facts about a city.",
    "input_schema": {
        "type": "object",
        "properties": {
            "city": {"type": "string"},
            "country": {"type": "string"},
            "population": {"type": "integer"},
        },
        "required": ["city", "country", "population"],
    },
}]

message = client.messages.create(
    model="claude-sonnet-5.5",
    max_tokens=4096,
    tools=tools,
    messages=[{"role": "user", "content": "Call save_city with the facts about Tokyo."}],
)

calls = [block for block in message.content if block.type == "tool_use"]
if calls:
    print(calls[0].input["city"], calls[0].input["population"])
else:
    print("No tool call, stop_reason:", message.stop_reason)

With tool_choice at auto, the model decides whether to call the tool, so keep the check for a missing tool_use block. How to send a tool's result back is in Tool calling.

Does prompt caching carry over?#

Not on its own. With Claude models, you mark what to cache by adding cache_control to a content block, and that field exists only in Messages. If your prompts repeat long instructions or documents, that alone is a reason to take route 2; see Prompt caching.

Does streaming work?#

Yes, on both routes. With the OpenAI SDK, stream=True works as before. With the Anthropic SDK, the messages.stream helper yields the text as it is written:

with client.messages.stream(
    model="claude-sonnet-5.5",
    max_tokens=4096,
    messages=[{"role": "user", "content": "Write a short poem about the sea."}],
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

The events behind it are in Streaming.

Common errors#

Every code is in Errors and fixes and Limits.

Test it with one request#

Before you change a large project, send one request with your Claude key. A reply means the base URL, the key and the model id are right:

curl --request POST "https://api.5abeer.ai/v1/messages" \
  --header "x-api-key: $KHABEER_API_KEY" \
  --header "Content-Type: application/json" \
  --header "anthropic-version: 2023-06-01" \
  --data '{"model":"claude-sonnet-5.5","max_tokens":512,"messages":[{"role":"user","content":"Write a product idea in one sentence."}]}'

{
  "id": "msg_01Xh7",
  "type": "message",
  "role": "assistant",
  "model": "claude-sonnet-5.5",
  "content": [
    {
      "type": "text",
      "text": "Hello! How can I help you today?"
    }
  ],
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 21,
    "output_tokens": 12
  }
}

Anthropic's OpenAI endpoint or 5abeer's?#

Anthropic runs its own OpenAI-compatible endpoint. Checked on 2026-11-03 in Anthropic's docs and ours:

Anthropic calls its layer "primarily intended to test and compare model capabilities" and points to its native API for the full feature set. The same holds here: the OpenAI SDK is the quick way in, and Messages is where Claude's own settings live.

What does the move cost?#

A 5abeer API key pays per token from your balance, and every model priced per token costs less than its official price. As an example, 3,000 requests to claude-sonnet-5.5, each with about 2,000 input tokens and 500 output tokens, thinking included:

Live prices are on Claude API, and What is a token shows how a request turns into tokens. Each key can have a spend limit, an expiry date and an IP allow-list, as in Control every key.

Plans are for the supported apps; to use the models from your own code, create an API key. For Claude in the terminal rather than in your code, see Claude Code.

FAQ#

Can I keep my OpenAI code and call Claude?#

Yes. Point the OpenAI SDK at https://api.5abeer.ai/v1, use a key for Claude models and pass a Claude model id. Chat Completions and Responses both work.

When is the Anthropic SDK worth the rewrite?#

When you need cache_control, thinking settings or output_config. For plain chat and tool calls, the three settings are enough, and one code path can still call several providers.

Why does Claude return 400 for a request that worked on GPT?#

The usual cause is a sampling setting or a forced tool call. Anthropic's newest models reject a non-default temperature or top_p, and a tool_choice that forces a tool. Remove them and try again.

Do I need a new key for Claude?#

Yes. A 5abeer key works with one provider's models, so a key for GPT models can't call Claude. Create one for Claude models; all your keys draw on the same balance.

Should I rewrite my prompts?#

Anthropic suggests reviewing them: a prompt tuned closely for GPT models may need changes to get the best from Claude. Try your main prompts with the test request above before you move the rest.

Sources#

Checked on 2026-11-03:

• Anthropic: OpenAI SDK compatibility
• Anthropic: Using the Messages API
• Anthropic: Define tools
• Anthropic: Thinking
• Anthropic: anthropic-sdk-python library
• OpenAI: openai-python library and openai-node library

Get started#

Create a key for Claude models, set it as KHABEER_API_KEY, run the test request above, then change the base URL and the model id across your project.