Feature request: Option to prefer subscription auth over ANTHROPIC_API_KEY

Summary

Request native configuration option to prefer subscription auth over environment API key, eliminating the need for env -u ANTHROPIC_API_KEY workaround.

Current Behavior

When ANTHROPIC_API_KEY is set in the environment, Claude Code CLI uses it for authentication instead of the subscription-based OAuth flow.

Problem scenario:

• User has API key set for other tools (Python scripts, direct API calls)
• User wants Claude Code to use their Claude subscription auth
• No native way to tell Claude Code to ignore the env API key

Current workaround:

alias claude='env -u ANTHROPIC_API_KEY /opt/homebrew/bin/claude'

This works but is non-obvious and requires shell knowledge.

Requested Behavior

Add configuration option to prefer subscription auth even when API key is present.

Option A: Config file setting

// ~/.claude/settings.json
{
  "auth": {
    "prefer_subscription": true
  }
}

Option B: CLI flag

claude --prefer-subscription "query"

Option C: Environment variable

export CLAUDE_CODE_PREFER_SUBSCRIPTION=true

Rationale

1. Common use case: Power users often have API keys for multiple purposes
2. Subscription benefits: Better rate limits, included in plan, no separate billing
3. Discoverability: Native config is more discoverable than env -u trick

Acceptance Criteria

• [ ] User can configure Claude Code to prefer subscription auth
• [ ] Configuration persists across sessions
• [ ] Works regardless of ANTHROPIC_API_KEY being set
• [ ] Documentation updated to explain auth precedence