visible auth/billing source indicator

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When a user has both an API key (ANTHROPIC_API_KEY) and a Max subscription, Claude Code silently uses the API key with no visual indicator of which billing source is active. I switched to Opus via /model expecting it to use my Max plan, but it burned through $20 in API credits instead. There's no way to tell at a glance whether you're on API billing or Max subscription billing.

Proposed Solution

The interface should show a persistent indicator of the active auth/billing source — something like [Auth: Max] or [Auth: API Key] in the status bar. When switching models with /model, if the active auth doesn't support the selected model under the current plan, Claude Code should warn the user before proceeding (e.g., "Opus is available on your API key but will consume API credits. Switch to Max auth with claude login?").

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_