OpenCode Third-Party API Quick Start: Configure an openai-compatible Provider

OpenCode is a terminal AI coding tool. It can connect to OpenAI-compatible APIs through provider configuration, so it can also use NixAPI’s multi-model endpoint.

This guide covers three tasks: install OpenCode, register a NixAPI provider, and configure a default model for terminal verification.

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Prerequisites

Check Node.js 18 or later:

node -v

Then create a NixAPI API Key in the NixAPI console. Copy model names from the NixAPI supported models page.

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Step 1: Install OpenCode

Install with npm:

npm install -g opencode-ai

On macOS or Linux, you can also use:

curl -fsSL https://opencode.ai/install | bash

Verify:

opencode -v

If a version is printed, continue.

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Step 2: Register a Custom Provider

Run:

opencode auth login

Follow the prompts:

1. Choose other from the provider list
2. Enter Provider ID: nixapi
3. Enter your NixAPI API Key

Use lowercase letters and numbers for the Provider ID. It must match the config file.

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Step 3: Edit opencode.json

The config file is usually:

• macOS / Linux: ~/.config/opencode/opencode.json
• Windows: C:\Users\your-name\.config\opencode\opencode.json

Add or merge:

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "nixapi": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "NixAPI",
      "options": {
        "baseURL": "https://nixapi.com/v1",
        "apiKey": "nix-your-api-key"
      },
      "models": {
        "claude-opus-4-7": {
          "name": "Claude Opus 4.7",
          "limit": {
            "context": 200000,
            "output": 32768
          }
        },
        "claude-sonnet-4-20250514": {
          "name": "Claude Sonnet 4",
          "limit": {
            "context": 200000,
            "output": 16384
          }
        },
        "gpt-5.4": {
          "name": "GPT 5.4",
          "limit": {
            "context": 128000,
            "output": 16384
          }
        }
      }
    }
  },
  "model": "nixapi/claude-sonnet-4-20250514"
}

Key points:

• nixapi must match the Provider ID from opencode auth login
• baseURL is https://nixapi.com/v1
• apiKey must be your real API Key
• The top-level model format is provider-id/model-id

If you prefer not to store the key in the config file, use OpenCode’s auth storage from opencode auth login. The inline version is easier for first-time debugging.

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Step 4: Start and Verify

Enter your project:

cd your-project
opencode

Then run:

/models

Confirm that the NixAPI provider models appear. Test with:

Read the current directory structure and write a short explanation for a new contributor.

If it replies normally, OpenCode is calling models through NixAPI.

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Add More Models

Add more entries under models, for example:

"deepseek-v4": {
  "name": "DeepSeek V4",
  "limit": {
    "context": 128000,
    "output": 8192
  }
},
"gemini-3-pro-preview": {
  "name": "Gemini 3 Pro Preview",
  "limit": {
    "context": 1000000,
    "output": 8192
  }
}

Adjust context and output limits for the model you use. Model IDs and prices should follow the NixAPI pricing page.

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Troubleshooting

Models do not appear

Check that opencode.json is valid JSON. Extra commas and missing quotes are common issues.

401

The API Key is wrong or not loaded. Run:

opencode auth login

or check the apiKey field in config.

404 or connection failure

Confirm:

"baseURL": "https://nixapi.com/v1"

Changes do not apply

Exit and restart OpenCode. Many terminal tools do not reload config files while running.

Cost control

Use a cost-effective model as the default, then switch to stronger models only for complex tasks. Check the NixAPI pricing page. NixAPI currently has a limited-time top-up exchange rate: RMB 0.80 = USD 1.00.

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Summary

OpenCode third-party API setup requires a nixapi provider in opencode.json, @ai-sdk/openai-compatible, https://nixapi.com/v1, and a model list. Once configured, OpenCode can use NixAPI models from the terminal.