[BUG] Claude Code Alters ANTHROPIC_API_KEY when it should not

Environment

• Platform (select one):
• [ ] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ X] Other: LiteLLM + Bedrock
• Claude CLI version: 1.0.22
• Operating System: macOS 15.5
• Terminal: macOS zsh

• Environment:

ANTHROPIC_BASE_URL set to a LiteLLM proxy endpoint
ANTHROPIC_API_KEY set to LiteLLM proxy API key
CLAUDE_CODE_USE_BEDROCK=True
CLAUDE_CODE_SKIP_BEDROCK_AUTH=True

Bug Description

When passing ANTHROPIC_API_KEY and ANTHROPIC_BASE_URL via the environment, claude code for some reason prepends sk-ant to the value passed in with ANTHROPIC_API_KEY. This obviously breaks

Steps to Reproduce

1. Set ANTHROPIC_API_KEY in environment
2. Run Claude Code with empty configuration
3. Claude Code will display with sk-ant- automatically prepended to whatever is in the environment variable with no way to remove it:

Detected a custom API key in your environment                                                                                                                                                        │
│                                                                                                                                                                                                      │
│ ANTHROPIC_API_KEY: sk-ant-...-abcdefg123456                                                                                                                                                  │
│                                                                                                                                                                                                      │
│ Do you want to use this API key?                                                                                                                                                                     │
│                                                                                                                                                                                                      │
│   1. Yes                                                                                                                                                                                             │
│ ❯ 2. No (recommended)✔                                                                                                                                                                               │
│                                                                                                                                                                                                      │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
   Enter to confirm ․ Esc to cancel

Expected Behavior

Claude Code should not alter the value in ANTHROPIC_API_KEY in any way and pass it exactly as entered.

Actual Behavior

Claude Code alters the value in ANTHROPIC_API_KEY with no way to change it

Additional Context

N/A