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Claude + GPT on One Endpoint: A 59API Quick Start

One integration, two model ecosystems

If your application needs both Claude and GPT, maintaining separate authentication, SDKs, and request formats adds unnecessary work. A unified API relay lets you reuse one client integration and select a different model for each request.

59API provides pay-as-you-go access through https://api.59api.com, with compatibility for OpenAI SDKs, Claude Code, and Codex. Positioned among the lowest-cost relays, it offers native, official-quality models rather than downgraded substitutes. Here is a practical path from account setup to your first model switch.

1. Collect your connection settings

Create a 59API account, generate an API key, and check the current model catalog. Record these three values before writing code:

• API key: Keep this server-side, in an environment variable or secret manager.
• OpenAI-compatible base URL: The service host is https://api.59api.com. Confirm the complete API prefix in the dashboard or documentation; if it specifies /v1, use https://api.59api.com/v1.
• Exact model identifiers: Copy one available Claude identifier and one GPT identifier. Display names such as Sonnet or Opus are not necessarily valid request values.

Store the verified base URL as API59_OPENAI_BASE_URL, your key as API59_KEY, and your initial model identifier as API59_MODEL. Avoid adding /v1 twice: the SDK appends resource paths to the base URL you supply.

2. Make one small request with the OpenAI SDK

For a Python quick start, install the client with pip install openai. With those environment variables set, run the following Python statements in order. They form one executable line:

import os; from openai import OpenAI; client = OpenAI(api_key=os.environ["API59_KEY"], base_url=os.environ["API59_OPENAI_BASE_URL"]); response = client.chat.completions.create(model=os.environ["API59_MODEL"], messages=[{"role":"user","content":"Reply with a one-sentence API health check."}], max_tokens=128); print(response.choices[0].message.content)

This uses the familiar Chat Completions interface. Check that your selected model supports that interface and its token-limit parameter; compatibility does not mean every model accepts every option. Keep the first request text-only and short so authentication and routing failures are easy to isolate.

3. Switch between Claude and GPT

Replace API59_MODEL with the other identifier and restart the script. The client, key, and request structure stay unchanged. In an application, pass the model identifier into a shared generation function rather than scattering provider-specific calls throughout your codebase.

Test both models on the same representative inputs: a code review, a structured extraction, and a short explanation. Compare correctness, latency, and recorded token usage. Start with plain text; then separately validate streaming, tool calls, and structured output before enabling them in production.

4. Connect Claude Code or Codex carefully

59API also supports Claude Code and Codex, but SDK compatibility is not a universal configuration recipe. Follow the relay's current instructions for each tool's authentication settings, endpoint format, and model selection. Do not assume an OpenAI-compatible URL belongs in every Claude Code configuration field.

Run a small, non-sensitive task first. Confirm that the tool reaches the intended model, then inspect usage before starting repository-wide work or an autonomous coding session.

5. Keep the low-cost setup predictable

• Compare actual charges: Check current input, output, and any caching rates. Low headline pricing is useful only when it matches your workload.
• Set application budgets: Limit output length, cap agent iterations, and avoid sending unchanged repository content repeatedly.
• Handle failures deliberately: Retry temporary rate limits or server failures with bounded exponential backoff. Fix authentication and invalid-model errors instead of retrying indefinitely.
• Review the relay boundary: Requests pass through another service. Check retention and privacy terms before sending customer data or proprietary code.

59API's pay-as-you-go pricing and referral rebate make it worth evaluating for cost-conscious development; check the rebate terms separately from inference rates. When you are ready, sign up and benchmark a small batch of real requests before moving production traffic.

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