🐛 Bug: Claude Code charges users twice - API billing AND prepaid credits consumed simultaneously

🐛 Bug Report: Double Billing on API-Based Login

Summary

Users on API-based billing (pay-per-usage) are being charged twice for every request — once via API billing (correct) and once via prepaid credits (incorrect).

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🔗 Related Issues

This issue has been reported multiple times but remains unresolved:

| Issue | Title | Relevance |
|-------|-------|-----------|
| #20976 | "Max plan shows as API Usage Billing" | EXACT same issue |
| #7719 | "API credits consumed despite Pro subscription" | Same dual-billing pattern |
| #5300 | "PRO account shows Credit balance too low" | Credit depletion on paid plans |

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📊 Evidence: Billing Proof

Test Session 1 (15 minutes of usage):

| Metric | Before | After | Change |
|--------|--------|-------|--------|
| Prepaid Credits | $1.53 | $1.12 | -$0.41 ❌ |
| API Usage | $8.71 | $9.12 | +$0.41 ✅ |

Test Session 2 (with forceLoginMethod: "console"):

| Metric | Before | After | Change |
|--------|--------|-------|--------|
| Login managed API key | $0.00 | $0.26 | +$0.26 |
| Prepaid Credits | $4.84 | $4.58 | -$0.26 ❌ |

Result: Exact dual charge — same amount charged to both payment methods even with forceLoginMethod set.

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🔄 Steps to Reproduce

1. Have API billing enabled ($100/month limit)
2. Log in to Claude Code using API-based billing (pay-per-usage)
3. Use Claude Code for 10-15 minutes
4. Check both:

• API billing: https://console.anthropic.com/settings/plans
• Prepaid credits: https://console.anthropic.com/settings/billing

Result: Both show charges for the same usage (approximately equal amounts)

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✅ Expected Behavior

• ✅ Only API usage increases
• ✅ Prepaid credits remain unchanged
• ✅ Single billing method

❌ Actual Behavior

• ❌ Both prepaid AND API usage increase
• ❌ Same usage charged twice
• ❌ Prepaid balance can go negative

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🔍 Root Cause Analysis (Suspected - Unconfirmed)

We suspect (but cannot confirm) this may be related to an authentication split:

Suspected Issue:

• Main Claude Code process: Uses API key → API Usage Billing ✅
• MCP OAuth servers: Use OAuth tokens from .credentials.json → Prepaid Credits ❌

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❌ Failed Fix Attempts

| Attempt | Action | Result |
|---------|--------|--------|
| 1 | Delete ~/.claude/.credentials.json | OAuth tokens regenerated automatically ❌ |
| 2 | Set "enableAllProjectMcpServers": false | OAuth tokens still regenerated ❌ |
| 3 | Empty OAuth credentials manually | Full OAuth configs restored from plugin files ❌ |
| 4 | Set "forceLoginMethod": "console" in settings.json | Dual billing still occurs ❌ |
| 5 | Export ANTHROPIC_API_KEY in ~/.zshrc | Key shows "Never used" - Claude Code ignores it and uses login managed key ❌ |
| 6 | Run /logout and restart | Still charges both API key AND prepaid credits ❌ |

Key Finding from Attempt 4-6:
Even with forceLoginMethod: "console" configured:

• Claude Code shows "API Usage Billing" in status bar ✅
• Login managed API key is charged ✅
• Prepaid credits STILL consumed ❌ (same amount deducted from both)
• Environment variable ANTHROPIC_API_KEY is completely ignored

Why Client-Side Fixes Don't Work:

• Official plugins are closed-source
• OAuth server URLs are hardcoded in plugin code
• No API key configuration option exists for plugins
• Plugins auto-load and override manual credential changes
• forceLoginMethod doesn't prevent OAuth-based charges

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💥 Impact

| Impact Area | Description |
|-------------|-------------|
| 💰 Financial | Users charged 2x for requests |
| 🔇 Silent Failure | No warning before credit depletion |
| ⚠️ Negative Balance | Users hit -$0.21 without ever buying credits |
| 🔒 Trust | Unexpected charges erode user confidence |

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🌍 Environment

• OS: macOS (likely affects all platforms)
• Claude Code Version: v2.1.31 (Feb 2026)
• Billing Type: API-based billing (pay-per-usage via console.anthropic.com)
• API Key: Configured in ~/.zshrc as ANTHROPIC_API_KEY
• Settings: forceLoginMethod: "console" in ~/.claude/settings.json
• Regression Started: ~February 2-3, 2026
• Frequency: 100% reproducible

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🙏 Requested Fix

1. Immediate: Audit billing routing to identify why dual charges occur
2. Root Cause: Ensure API billing users are only charged via API billing
3. Refund: Consider refunding incorrectly charged prepaid credits for affected users

Potential Solutions (for Anthropic team to evaluate):

• Option 1: Make OAuth MCP servers use API billing when API key is present
• Option 2: Allow API key auth for official plugins instead of OAuth
• Option 3: Skip prepaid charges for OAuth requests when API billing is enabled

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📎 Additional Notes

• This is a regression — worked correctly before Feb 2-3, 2026
• Possibly related to Jan 2026 platform changes that restricted OAuth tokens to Claude Code only
• The issue is server-side — no client-side workaround available
• Only working workaround: Uninstall OAuth-based plugins (but loses valuable integrations)

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🔄 Additional Issue: Broken /login Flow

When running /login command and selecting "Anthropic Console account • API usage billing":

Expected: Should provide an API key token to copy for authorization
Actual: Redirects to "Buy credits to get started" page

This indicates the system is incorrectly routing API billing users through the credits purchase flow instead of the API key authorization flow.