[BUG] Opus 4.5 model uses hardcoded "us." prefix instead of ANTHROPIC_DEFAULT_OPUS_MODEL environment variable

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When selecting "Opus 4.5" in Claude Code's /model menu with AWS Bedrock integration, it uses a hardcoded model ID (us.anthropic.claude-opus-4-5-20251101-v1:0) instead of respecting the ANTHROPIC_DEFAULT_OPUS_MODEL environment variable configured in ~/.claude/settings.json. This results in an API error: "The provided model identifier is invalid."

Meanwhile, "Opus 4.1" correctly uses the environment variable and works fine.

What Should Happen?

Both Opus 4.1 and Opus 4.5 should respect the ANTHROPIC_DEFAULT_OPUS_MODEL environment variable (global.anthropic.claude-opus-4-5-20251101-v1:0), consistent with how Sonnet and Haiku models work.

Error Messages/Logs

Steps to Reproduce

1. Set up AWS Bedrock integration with Claude Code
2. Configure ~/.claude/settings.json with ANTHROPIC_DEFAULT_OPUS_MODEL: "global.anthropic.claude-opus-4-5-20251101-v1:0"
3. Run /model and select "Opus 4.5"
4. Observe: API error with "us.anthropic.claude-opus-4-5-20251101-v1:0"
5. Run /model and select "Opus 4.1"
6. Observe: Works correctly with global.anthropic.claude-opus-4-5-20251101-v1:0

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

v2.1.15

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

{
"env": {
"CLAUDE_CODE_USE_BEDROCK": "1",
"AWS_REGION": "ap-northeast-2",
"AWS_PROFILE": "Charles",
"ANTHROPIC_MODEL": "global.anthropic.claude-haiku-4-5-20251001-v1:0",
"ANTHROPIC_DEFAULT_SONNET_MODEL": "global.anthropic.claude-sonnet-4-5-20250929-v1:0",
"ANTHROPIC_DEFAULT_HAIKU_MODEL": "global.anthropic.claude-haiku-4-5-20251001-v1:0",
"ANTHROPIC_DEFAULT_OPUS_MODEL": "global.anthropic.claude-opus-4-5-20251101-v1:0",
"ANTHROPIC_SMALL_FAST_MODEL": "global.anthropic.claude-haiku-4-5-20251001-v1:0",
"CLAUDE_CODE_MAX_OUTPUT_TOKENS": "4096",
"MAX_THINKING_TOKENS": "1024"
}
}