Gemini CLI is showing errors:

Error: Authentication failed

Or it is not working as expected. Here is how to fix it.

Fix 1: Check installation

# Check if Gemini CLI is installed
gemini --version

# If not installed
npm install -g @anthropic-ai/gemini-cli

# Or use Antigravity (replacement)
npm install -g @anthropic-ai/antigravity

Note: Gemini CLI was replaced by Antigravity CLI in June 2026. See our migration guide.

Fix 2: Authenticate

# Login with Google account
gemini auth login

# Or set API key
export GOOGLE_API_KEY="your-key"

Fix 3: Check API key

# Verify key is set
echo $GOOGLE_API_KEY

# Test the key
curl "https://generativelanguage.googleapis.com/v1/models?key=$GOOGLE_API_KEY"

Fix 4: Fix model selection

# Use specific model
gemini --model gemini-3.6-flash

# List available models
gemini models

Fix 5: Check network

# Test connection to Google APIs
ping generativelanguage.googleapis.com

# Check firewall
curl -I https://generativelanguage.googleapis.com

Fix 6: Clear cache

# Clear Gemini CLI cache
rm -rf ~/.gemini/cache

# Restart
gemini

Fix 7: Update to Antigravity

Gemini CLI is deprecated. Migrate to Antigravity:

# Uninstall Gemini CLI
npm uninstall -g @anthropic-ai/gemini-cli

# Install Antigravity
npm install -g @anthropic-ai/antigravity

# Authenticate
antigravity auth login

See our complete Antigravity guide for migration details.

Still not working?

1. Check Google AI status — aistudio.google.com
2. Use AI Studio — Browser-based alternative
3. Try different network — Some regions have better access
4. Contact support — Google AI support

FAQ

Is Gemini CLI still supported?

No. Gemini CLI was replaced by Antigravity CLI in June 2026. Existing installations still work, but new features and model updates go to Antigravity. See our migration guide for details.

How do I authenticate with Gemini CLI?

Use gemini auth login to authenticate with your Google account. If you have a Google AI API key, set it with export GOOGLE_API_KEY="your-key".

What is the difference between Gemini CLI and Antigravity?

Antigravity is the replacement for Gemini CLI. It has the same core functionality but with better model support, improved performance, and new features. All new development goes to Antigravity.

Related: Antigravity Complete Guide · Migrate Gemini CLI to Antigravity · Gemini 3.6 Flash Complete Guide · Best AI Coding Tools 2026