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DeepSeek Harness (command: dsh) supports OpenAI-compatible model providers. After completing this guide, you can use models such as deepseek-flash, deepseek-v4-flash, gpt-6-astra, and gpt-5.6-sol through Syon while keeping the Harness web interface, sessions, and agent capabilities. Supported models
  • DeepSeek: deepseek-flash (DeepSeek V4.1 Flash), deepseek-v4-pro (August 13 official release), deepseek-v4-flash (July 31 official release)
  • GPT: gpt-6-astra, gpt-5.6-sol, gpt-5.6-luna, gpt-5.6-terra, gpt-5.5

1. Prerequisites

Before you begin, install Node.js 24 and prepare a valid Syon API key.

1.1 Install Node.js 24

DeepSeek Harness requires Node.js 24. npm is included with Node.js. Download the installer for your operating system and CPU architecture: When using the China mirror, select a v24.x.x directory and download the installer for your system. After installation, reopen your terminal and check the versions: bash
The output of node --version should start with v24.. Syon API keys start with sk-. You can create one in the Syon dashboard. Create a Syon API key

2. Configure and start in one step

You do not need to open or manually edit any configuration files. Replace sk-replace-with-your-api-key in the code block with your Syon API key, then copy and run the entire command in your terminal. It installs, configures, and starts DeepSeek Harness automatically. macOS / Linux bash
Windows PowerShell powershell
The command installs DeepSeek Harness, backs up and merges any existing configuration, stores your key, configures the Syon models, and starts Harness. It does not remove your existing theme or other settings. After startup, the terminal displays a local URL, usually http://127.0.0.1:3080. Open it in your browser and create a new session. To start Harness again later, run this command from your project directory: bash
To use Harness in a specific project, change to the actual project directory before running dsh web. Do not copy /path/to/my-project literally; it is only a placeholder.

3. Verify the connection

Send a minimal request in headless mode to verify the configuration, API key, and model: bash
If the terminal returns OK, DeepSeek Harness has successfully called a model through Syon. Run dsh web to open the web interface.

4. Add and switch models

To choose from multiple Syon models in Harness, add them to the same models list. This example includes DeepSeek V4.1 Flash, DeepSeek V4 models, and several GPT models: yaml
Change agent-default-model.model to set the default model for new sessions. Existing sessions may continue using their original model. After changing the default, refresh the page and create a new session, or switch models manually from the model selector. Syon’s model catalog is updated continuously. To confirm the current model IDs, run: bash

5. Troubleshooting

The API returns 401 or invalid_bearer_token. Make sure the API key is complete, contains no extra spaces, has not been deleted, and starts with sk-. If the error continues, create a new key in the Syon dashboard and try again.