How to Run Local AI Models with Ollama and OpenCode

Step-by-step guide on how to run local LLMs with Ollama and using them via OpenCode.

Table of contents

Why Run Local AI Models?

Pros

• Total Privacy: Your code and prompts never leave your machine. No data sent to OpenAI, Anthropic, or any third party.
• No Rate Limits: Process as many requests as your hardware can handle. No API quotas or throttling.
• Offline Capable: Works without internet once the model is downloaded. Perfect for travel or restricted networks.
• Zero Cost: No API fees or subscriptions. The only cost is your electricity and hardware.
• Customizable: Swap models freely. Run fine-tuned variants or experimental models that cloud providers don’t offer.

Cons

• Resource Intensive: Local models consume RAM and GPU memory. A 9.6GB model needs ~10GB free RAM to run comfortably.
• Hardware Requirements: Bigger models need better specs. A 70B parameter model needs 40GB+ VRAM (RTX 4090 territory). Consumer GPUs cap out at smaller models.
• Less Capable: Local models lag behind frontier models (Claude 3.7 Sonnet, GPT-4o, o3). Complex reasoning, math, and edge cases suffer.
• Slower Inference: Even on an RTX 3060, local models are slower than API responses. Expect 3-10s per response for 8B models.
• Manual Maintenance: You manage updates, model downloads, and troubleshooting. No “it just works” experience.

The Trade-off

Use local models when: Privacy matters, you process sensitive code, or you want zero ongoing costs.

Use cloud APIs when: You need maximum capability, fastest responses, or don’t want to manage hardware.

This guide focuses on the local approach with a mid-range setup (RTX 3060 + 32GB RAM) running an 8B parameter model—balanced for everyday coding assistance without cloud dependency.

Prerequisites

My setup:

Minimum requirements:

• macOS, Linux, or Windows with terminal access
• GPU — inference on CPU is 10-50x slower than GPU
• Sufficient RAM for your chosen model (16GB+ recommended for 8B parameter models)

Why a good GPU matters:

Local AI models are compute-intensive. A dedicated NVIDIA GPU with CUDA cores (or Apple Silicon with Metal) dramatically speeds up token generation:

• With GPU (RTX 3060): 10-30 tokens/second — interactive, responsive coding help
• Without GPU (CPU only): 1-5 tokens/second — sluggish, painful for long responses

VRAM is the limiting factor. The model must fit entirely in GPU memory to run efficiently. The 9.6GB gemma4:e4b model fits comfortably in an RTX 3060’s 12GB VRAM. Larger models (13B, 70B) require proportionally more VRAM (24GB, 48GB+).

Check your specs:

# OS version
lsb_release -a

# CPU info
lscpu | grep "Model name\|CPU(s)"

# RAM
free -h

# GPU (if NVIDIA)
nvidia-smi -L

Step 1: Install Ollama

Download and install Ollama using the official install script:

curl -fsSL https://ollama.com/install.sh | sh

Source: https://ollama.com/

Note: This installs Ollama as a system service that runs in the background.

What this does:

• Creates ollama system user
• Adds user to ollama, render, and video groups (for GPU access)
• Sets up systemd service to auto-start Ollama
• Detects NVIDIA GPU for CUDA acceleration

Step 2: Pull a Model

Browse available models at https://ollama.com/search. For this guide, we’ll use Gemma 4 e4b — the 8B parameter, Q4_K_M quantized variant tagged as latest.

Tag explanation: Ollama uses Docker-style tagging. gemma4 or gemma4:latest pulls the default variant. Explicit tags like gemma4:e2b or gemma4:26b pull specific sizes.

Run the command to pull the model:

ollama pull gemma4:e4b

Model specs (gemma4:e4b):

Download complete:

Note: First pull downloads ~9.6 GB. Subsequent runs are instant (model cached locally).

Step 3: Test the Model (Interactive Mode)

Run the model interactively to verify it’s working:

ollama run gemma4:e4b

This drops you into a chat session with the model. Try asking it something:

>>> Why is the sky blue?

Expected behavior:

Gemma 4 shows its reasoning process before responding:

Chain-of-thought reasoning displayed during generation

Then outputs a formatted, detailed answer:

Formatted response with markdown headers, emojis, and blockquotes

To exit: press Ctrl+D or type /bye.

Step 4: Install OpenCode

OpenCode is an AI coding harness that works with local models via Ollama.

Install via the official script:

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

Source: https://opencode.ai/

Installation progress:

OpenCode installed and added to PATH

The installer automatically adds OpenCode to your shell PATH (.zshrc in this case).

Step 5: Configure OpenCode to Use Ollama

Create the OpenCode configuration file to connect to your local Ollama instance:

mkdir -p ~/.config/opencode
cat > ~/.config/opencode/opencode.json << 'EOF'
{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "ollama": {
      "npm": "@ai-sdk/openai-compatible",
      "name": "Ollama",
      "options": {
        "baseURL": "http://localhost:11434/v1"
      },
      "models": {
        "gemma4:e4b": {
          "name": "gemma4:e4b"
        }
      }
    }
  }
}
EOF

Important: The JSON key in the models section must match the Ollama model name exactly, including the colon (:). Using gemma4-e4b (with hyphen) will cause a “model not found” error. Always use gemma4:e4b (with colon).

Note: Make sure Ollama is running (check with ollama list to see model names). The systemd service started automatically after installation.

Launch OpenCode

opencode

Initial interface:

OpenCode v1.3.17 main interface on first launch

The interface shows:

• Central input box: “Ask anything…”
• Agent modes: Build (selected by default)
• Keyboard shortcuts: tab for agents, ctrl+p for commands

Switch to Your Local Model

Type /models or select it from the list.

Model selection screen:

Local gemma4:e4b appears under the Ollama section

The model picker shows:

• OpenCode Zen section: Cloud models (Big Pickle, MiniMax, Nemotron, Qwen)
• Ollama section: Your local gemma4:e4b model (highlighted)

Select gemma4:e4b and press Enter. OpenCode will now use your local model for all requests.

Verification: Local Model Working

Once selected, start a conversation. The chat interface will show:

OpenCode successfully using local gemma4:e4b via Ollama — generating a Python learning plan

Confirmation signs:

• Model indicator: Bottom status shows Build gemma4:e4b Ollama
• Response metadata: Shows structured output with sections, emojis, and formatted text
• Zero cost: No API calls, pure local inference on your hardware
• Token tracking: Context window usage displayed in sidebar

Note: If you see model 'gemma4-e4b' not found, the JSON key in your config has a hyphen instead of a colon. Fix: use "gemma4:e4b": as the key (not "gemma4-e4b":).

Testing: Build a Note-Taking App

Verify your local model can generate working code. In OpenCode with your local model selected, paste:

Create a simple note-taking app using vanilla JavaScript, HTML, and CSS.
Do not use web search — just write the code directly.

Requirements:
- Input field to add new notes
- Display list of saved notes with timestamps
- Delete button for each note
- Save to localStorage (persist after page refresh)
- Clean, centered layout (max-width 600px)
- No external libraries — pure vanilla JS/CSS

Provide the complete code as a single HTML file.

Local model generating code:

Gemma 4 26B model generating a complete note-taking app with HTML, CSS, and JS

The model outputs a complete, runnable HTML file with:

• HTML5 boilerplate
• Embedded CSS with custom properties (:root variables)
• Vanilla JavaScript for DOM manipulation and localStorage

Generated app running in browser:

Working note-taking app generated by the local Gemma 26B model

The gemma4:26b model created this note-taking tool in 3m 29s. It may not look fancy, but it works! — add notes, delete them, timestamps appear automatically, and data persists after refresh and it even added a nice keyframes fade-in animation.

Features that work:

• Add notes via input field
• Automatic timestamps on each note
• Delete buttons (red X) remove individual notes
• Data persists in localStorage (survives page refresh)
• Clean, centered layout (~600px max-width)
• Smooth animations when adding notes

Troubleshooting

Issue: model 'gemma4-e4b' not found

Cause: The JSON key in opencode.json uses a hyphen instead of the exact Ollama model name.

Solution: Ensure the JSON key matches the model name exactly, including the colon:

// Wrong ❌
"models": {
  "gemma4-e4b": {
    "name": "gemma4:e4b"
  }
}

// Correct ✅
"models": {
  "gemma4:e4b": {
    "name": "gemma4:e4b"
  }
}

Issue: Ollama connection refused

Cause: Ollama service not running.

Solution: Check Ollama status:

sudo systemctl status ollama
ollama list

If not running:

sudo systemctl start ollama

Issue: Slow response times

Cause: First run loads model into memory; subsequent runs are faster.

Solution: Keep Ollama running. The model stays cached in RAM after first use.