Feature Request: Runtime switch between Subscription and Vertex/API billing

Problem

When using Claude Code with Vertex AI (CLAUDE_CODE_USE_VERTEX=1), there is no way to switch back to Subscription billing without restarting the CLI. The only workaround is toggling the environment variable and restarting.

Meanwhile, when on a Subscription plan and the included quota is exhausted, Claude Code does offer an interactive prompt to enable extra usage (overflow to API billing). This shows the infrastructure for runtime billing switches exists — but only in one direction.

Expected Behavior

A command or toggle (e.g. /switch-billing, /account, or similar) that allows switching between configured billing providers (Subscription ↔ Vertex/API) at runtime without restarting the CLI.

Current Workaround

export CLAUDE_CODE_USE_VERTEX=0  # switch to subscription
export CLAUDE_CODE_USE_VERTEX=1  # switch to vertex
# then restart claude

Requires full CLI restart each time.

Why This Matters

Users who have both a Subscription (Pro/Max) and Vertex/API configured want to flexibly switch — e.g. use Subscription quota first, then switch to Vertex when exhausted, or vice versa. The current UX is asymmetric: overflow from Subscription is smooth, but switching back requires manual env var changes and a restart.