Evaggelos Balaskas - System Engineer

If you want to use Claude Code together with Osaurus, there are two different pieces to understand:

1. Model backend — the LLM that answers your prompts
2. MCP tools — the tools Claude Code can call

This is the most important idea:

• Osaurus MCP gives Claude Code access to tools
• Osaurus API can also be used as the model backend, if your setup supports it

These are separate.

Install Claude Code and Osaurus

Let’s start by installing both tools via homebrew on a macbook.

Disclaimer: I like asaurus because it’s small and amazing, I find Ollama big and ugly in macbook.

claude code installation

brew install --cask claude-code

osaurus

brew install --cask osaurus

Open osaurus ui to setup osaurus, in this blog post we will not cover this.

language models

At some point you will download a couple LLMs or SLMs to start with osaurus and you should already have install some tools.

curl -s http://localhost:1337/v1/models | jq .

{
  "data": [
    {
      "id": "llama-3.2-3b-instruct-4bit",
      "created": 1772877371,
      "object": "model",
      "owned_by": "osaurus",
      "root": "llama-3.2-3b-instruct-4bit"
    },
    {
      "id": "qwen3-vl-4b-instruct-8bit",
      "created": 1772877371,
      "object": "model",
      "owned_by": "osaurus",
      "root": "qwen3-vl-4b-instruct-8bit"
    },
    {
      "id": "qwen3.5-0.8b-mlx-4bit",
      "created": 1772877371,
      "object": "model",
      "owned_by": "osaurus",
      "root": "qwen3.5-0.8b-mlx-4bit"
    }
  ],
  "object": "list"
}

status

❯ osaurus status
running (port 1337)

tools

❯ osaurus tools list
osaurus.browser  version=1.2.0
osaurus.fetch  version=1.0.2
osaurus.filesystem  version=1.0.3
osaurus.git  version=1.0.3
osaurus.images  version=1.0.3
osaurus.macos-use  version=1.2.1
osaurus.search  version=1.0.4
osaurus.time  version=1.0.3
osaurus.vision  version=1.0.1

Connect Claude Code to Osaurus via a MCP server

So by default claude code with autostart an interactive configuration setup to connect with your anthropic subscription or with any major ai subscription. We want to override this behaviour to enable claude to connect with osaurus. best way to do that is via an mcp server.

Create ~/.claude.json:

cat > ~/.claude.json <<EOF
{
  "theme": "dark-daltonized",
  "hasCompletedOnboarding": true,
  "mcpServers": {
    "osaurus": {
      "command": "osaurus",
      "args": [
        "mcp"
      ]
    }
  }
}
EOF

This tells Claude Code to start Osaurus as an MCP server.

Note on hasCompletedOnboarding: Setting this to true prevents a startup error where Claude Code tries to connect to Anthropic’s servers before your local endpoint is configured. It is not required for the MCP setup itself, but it avoids a confusing first-run failure.

Note on MCP config location: MCP servers must be defined in ~/.claude.json (or a project-local .mcp.json). Placing them in ~/.claude/settings.json will not work — that file is for environment variables and permissions, not MCP server definitions.

Configure Claude Code to use Osaurus as the model endpoint

Create ~/.claude/settings.json:

mkdir -p ~/.claude/

cat > ~/.claude/settings.json <<EOF
{
  "env": {
    "ANTHROPIC_BASE_URL": "http://127.0.0.1:1337",
    "ANTHROPIC_AUTH_TOKEN": "osaurus",
    "ANTHROPIC_MODEL": "qwen3-vl-4b-instruct-8bit"
  }
}
EOF

This does three things:

• points Claude Code to your local Osaurus server
• authenticates with the local Osaurus endpoint using a static token
• selects the model to use

Note on ANTHROPIC_MODEL vs ANTHROPIC_DEFAULT_SONNET_MODEL: ANTHROPIC_MODEL sets the model directly and is the simpler choice when Osaurus exposes a single model. ANTHROPIC_DEFAULT_SONNET_MODEL overrides only the model Claude Code uses when it internally requests a “sonnet”-class model — useful if you want different models for different internal roles, but unnecessary for a basic local setup.

and

Claude Code requires custom auth token values to be explicitly approved. ANTHROPIC_AUTH_TOKEN is for that

Without this, Claude Code may still prompt for authentication even though your token is set.

Start Claude Code

Run:

claude

Inside Claude Code, you can check your setup with:

/status

Simple mental model

Think of it like this:

• Model = the brain
• MCP = the toolbox

Changing the model does not remove the tools.

That is enough to get started.

Brave’s built-in privacy-first AI assistant, Leo, supports connecting to a local OpenAI-compatible server. This means your conversations never leave your machine — no cloud, no telemetry, just your browser talking to your own model.

This guide uses Osaurus on a MacBook M4 Pro, running the qwen3.5-0.8b-mlx-4bit model as a local example. Any OpenAI-compatible local server (LM Studio, Ollama, llama.cpp, etc.) will work the same way.

About the Model

Qwen3.5-0.8B is Alibaba’s latest small language model, released in March 2026. Despite its compact size, it is a native multimodal model — meaning it supports both text and vision (image understanding) out of the box. It runs efficiently on Apple Silicon via MLX quantization, making it an excellent fit for local inference on a MacBook M4 Pro with minimal RAM usage.

The mlx-4bit suffix means the model weights are 4-bit quantized for Apple Silicon using the MLX framework — fast, low-memory, and runs entirely on-device.

Prerequisites

• Brave Browser installed (check latest version)
• A local LLM server running and reachable at http://localhost:<port>
• Your server responds to POST /v1/chat/completions (OpenAI-compatible API)

Verify your server is working before continuing:

curl -s -X POST http://localhost:1337/v1/chat/completions
  -H "Content-Type: application/json"
  -d '{
    "model": "qwen3.5-0.8b-mlx-4bit",
    "messages": [{"role": "user", "content": "Say hello"}]
  }' | jq .

You should get a JSON response with a choices[0].message.content field. If that works, you’re ready.

example output

{
  "id": "chatcmpl-88053214C2DC",
  "object": "chat.completion",
  "created": 1772783955,
  "model": "qwen3.5-0.8b-mlx-4bit",
  "choices": [
    {
      "finish_reason": "stop",
      "message": {
        "content": "Hello! How can I help you today? 😊",
        "role": "assistant"
      },
      "index": 0
    }
  ],
  "usage": {
    "prompt_tokens": 2,
    "completion_tokens": 8,
    "total_tokens": 10
  }
}

Step 1 — Enable Required Brave Flags

Before Leo can connect to a local server, you need to enable two feature flags in Brave.

Open a new tab and go to:

brave://flags

Search for and enable each of the following:

After enabling both flags, click Relaunch to restart Brave.

Step 2 — Open Leo Settings

Once Brave restarts, open Leo settings by navigating to:

brave://settings/leo-ai

Or open the Leo sidebar (chat bubble icon) → click the Settings gear icon.

Step 3 — Add a Custom Model

In the Leo settings page, scroll down to Bring your own model and click Add new model.

Fill in the fields as follows:

Click Save model.

Note: The server endpoint must be the full path including /v1/chat/completions, not just the base URL.

Step 4 — Select Your Local Model

Back in the Leo chat panel:

1. Click the model selector dropdown (shows the currently active model name).
2. Select the model you just added — e.g. Osaurus.

Leo will now route all requests to your local server.

Step 5 — Start Chatting

Type a message in the Leo input box and press Enter.

How It Works

Your request goes to http://localhost:1337/v1/chat/completions — entirely on your machine. Nothing is sent to Brave’s servers or any external service.

You type in Leo
      │
      ▼
Brave sends POST /v1/chat/completions
      │
      ▼
localhost:1337  (your local server — Osaurus)
      │
      ▼
Model inference on Apple Silicon (MLX / 4-bit quantized)
      │
      ▼
Response streams back to Leo in your browser

No internet required after setup. No data leaves your device.

Tips

• Model name must match exactly what your server reports — check it with:

curl http://localhost:1337/v1/models | jq .

eg.

{
  "data": [
    {
      "object": "model",
      "id": "llama-3.2-3b-instruct-4bit",
      "created": 1772791159,
      "root": "llama-3.2-3b-instruct-4bit",
      "owned_by": "osaurus"
    },
    {
      "object": "model",
      "id": "qwen3.5-0.8b-mlx-4bit",
      "created": 1772791159,
      "root": "qwen3.5-0.8b-mlx-4bit",
      "owned_by": "osaurus"
    }
  ],
  "object": "list"
}

• Leo context features (summarize page, ask about selected text) also work with local models — Leo includes the page content as part of the prompt automatically.
• Since Qwen3.5-0.8B supports vision, with Vision Support enabled you can paste or drag images into Leo and the model will analyze them — all locally.
• Start your local server before opening Brave, or you’ll get a connection error when Leo tries to reach it.

That’s it. You now have a fully local, private AI assistant inside your browser — no accounts, no subscriptions, no data leaving your machine.