Gemini CLI vs Claude Code Comparison

# Gemini CLI - install, authentication, and MCP/subagent configuration
npm install -g @google/gemini-cli

# Login: start the CLI, choose "Sign in with Google" at launch
# (there's no separate `auth login` subcommand)
gemini

# Running with an API key (choose "Use Gemini API key" inside the CLI)
export GEMINI_API_KEY="YOUR_GEMINI_API_KEY"
gemini

# Add an MCP server and run the agent inside the repo
gemini mcp add postgres -- npx -y @modelcontextprotocol/server-postgres \
  "postgresql://localhost/mydb"

gemini "Find and fix the failing tests in this repo" --yolo

# Overriding a built-in subagent - .gemini/settings.json
{
  "agents": {
    "overrides": {
      "codebase_investigator": {
        "modelConfig": { "model": "gemini-3-flash-preview" },
        "runConfig": { "maxTurns": 50 }
      }
    }
  }
}

# Custom subagents are defined in .gemini/agents/<name>.md with YAML frontmatter

# Enterprise authentication with Vertex AI
export GOOGLE_GENAI_USE_VERTEXAI=true
export GOOGLE_CLOUD_PROJECT="my-gcp-project"
gemini

# Claude Code - install, model selection, and subagent/MCP usage
npm install -g @anthropic-ai/claude-code

# Start with the default model (Sonnet 5 for exploration, Opus 5.5 for specced code)
claude

# Starting with a specific model/alias
claude --model opus          # Opus 5.5 (default Opus)
claude --model fable         # Fable 5.1 (top tier)

# Adding an MCP server from the Anthropic Directory
claude mcp add postgres -- npx -y @modelcontextprotocol/server-postgres \
  "postgresql://localhost/mydb"

# Parallel exploration + specced code using subagents
# (built-in: Explore, Plan, General-purpose)
claude "Scan the auth module with the Explore subagent, then draft a
migration plan with the Plan subagent" --permission-mode plan

# Overriding the subagent model via an env variable
export CLAUDE_CODE_SUBAGENT_MODEL=claude-sonnet-5
claude "Find unused exports across the repo"

# Running headless for CI/automation
claude -p "run lint + tests, fix the errors" --output-format json