Claude Pro subscription: API billing allowed instead of being blocked

Description

When running Claude Code with a Claude Pro subscription (claudepro), the CLI still permitted usage under API billing. The expected behavior is that API billing should be refused and the user should be directed to use claudeapi with an explicit API key instead.

Expected Behavior

• Claude Code detects active Claude Pro subscription
• Refuses to fall back to API billing
• Suggests switching to claudeapi billing mode if API usage is intended

Actual Behavior

• Claude Code allowed API billing to proceed without warning or refusal
• No prompt to switch billing modes

Environment

• OS: Windows 11 Pro
• Claude Code: CLI
• Subscription: Claude Pro
• Shell: bash (via Windows)

Notes

ANTHROPIC_API_KEY was not set in the environment at time of testing, so the fallback trigger is unclear. This may be a billing mode enforcement gap in the CLI.

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