Claude Code Desktop Third-Party API Quick Start: Base URL, Key, and Model Setup

Configure Claude Code Desktop with a third-party Base URL, API Key, and model ID, then verify calls to Claude, GPT, Gemini, and other models.

Claude Code Desktop supports custom model endpoints through its settings UI. By entering a NixAPI Base URL and API Key, you can use Claude, GPT, Gemini, DeepSeek, and other models from the desktop app.

This guide is for users who prefer the graphical settings panel over editing configuration files.

Prerequisites

Make sure you have:

Claude Code Desktop installed
A NixAPI API Key
A version of Claude Code Desktop that supports custom API, provider, or endpoint settings

If you do not have a key, create one from the NixAPI console. A name such as claude-code-desktop makes usage easier to identify later.

Step 1: Open Settings

Start Claude Code Desktop and open settings. Depending on your system and version, the entry may be:

A gear icon in the top-right corner
Settings in the macOS menu bar
An API or Provider settings entry near the bottom of the sidebar

Look for fields such as:

Model Provider
API Base URL
Endpoint
API Key
Model

The labels may vary, but the meaning is the same.

Step 2: Enter NixAPI Details

Fill in:

Field	Value
API Base URL / Endpoint	`https://nixapi.com/v1`
API Key / Auth Token	`nix-your-api-key`
Model	For example, `claude-sonnet-4-20250514`

The Base URL must include /v1:

https://nixapi.com/v1

Do not enter only https://nixapi.com, and do not add extra spaces.

Suggested models:

claude-sonnet-4-20250514
claude-opus-4-7
gpt-5.4
gemini-3-pro-preview
deepseek-v4

The full model list and prices are available on the NixAPI supported models page.

Step 3: Save and Test

Save the settings. Return to the main Claude Code Desktop window, start a new chat, and send:

Hello. Explain in three sentences how you can help me write code.

If a response appears within a few seconds, the desktop app is calling the model through NixAPI.

If the app keeps loading, fully quit and reopen it. Some desktop apps only load API settings on startup.

Step 4: Switch Models by Task

Once the endpoint and key are configured, you usually only need to change the model:

Daily coding tasks: claude-sonnet-4-20250514
Complex architecture or refactoring: claude-opus-4-7
General text and code tasks: gpt-5.4
Long-context experiments: gemini-3-pro-preview
Cost-sensitive work: check the NixAPI model pricing page

NixAPI currently has a limited-time top-up exchange rate: RMB 0.80 = USD 1.00. Check your balance before continuous coding sessions.

Troubleshooting

`401 Unauthorized`

The API Key is invalid or incomplete. Copy it again from the NixAPI console, and make sure it has no leading or trailing spaces.

`404 Not Found`

Check the Base URL:

https://nixapi.com/v1

Missing /v1 is the most common cause.

`model not found`

The model ID does not match the platform list. Copy the exact ID from the NixAPI supported models page.

Settings do not apply

Fully quit Claude Code Desktop and reopen it. Closing the window may not reload the configuration.

Timeout on a company or campus network

Try another network. If curl cannot reach https://nixapi.com/v1 either, the problem is likely at the network layer.

Summary

Claude Code Desktop third-party API setup is simple: enter https://nixapi.com/v1, an API Key, and a model ID, save, then restart and test. After that, switching models only requires changing the model name.

Claude Code Desktop Third-Party API Quick Start: GUI Configuration