[BUG] Hardcoded `us.` prefix in Haiku model ID causes AWS Bedrock authentication failures for multi-agents

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 using Claude Code with AWS Bedrock, spawning multi-agents (via the Task tool) fails with a 400 error because the Haiku model ID is hardcoded with the deprecated us.anthropic. prefix instead of the correct global.anthropic. prefix. The main conversation works fine, but any sub-agents immediately fail

What Should Happen?

Multi-agents should successfully spawn and execute using the AWS Bedrock model ID with the global. prefix:
global.anthropic.claude-3-5-haiku-20241022-v1:0
This would match the modern AWS Bedrock cross-region inference model ID format.

Error Messages/Logs

API Error (us.anthropic.claude-3-5-haiku-20241022-v1:...): 400 The provided model identifier is invalid.

Steps to Reproduce

Environment Setup:

# Set environment variables
export ANTHROPIC_MODEL="global.anthropic.claude-sonnet-4-5-20250929-v1:0"
export CLAUDE_CODE_USE_BEDROCK=1
export AWS_DEFAULT_REGION="eu-central-1"

Steps:

1. Start Claude Code:

claude

1. Attempt to spawn any multi-agent by using a command that invokes the Task tool. For example:

User: "Can you use the claude-code-guide agent to look up how hooks work?"

1. Observe the immediate error:

API Error (us.anthropic.claude-3-5-haiku-20241022-v1:...): 400 The provided model identifier is invalid.

1. Note that the main conversation (using Sonnet) works fine - only sub-agents fail.

Minimal Example:

Any Task tool invocation will reproduce this. The simplest way:

• Main model (Sonnet with global. prefix): ✅ Works
• Sub-agent model (Haiku with hardcoded us. prefix): ❌ Fails

Claude Model

Sonnet (default)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.0.71 (Claude Code)

Platform

AWS Bedrock

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

Additional Information

Configuration:

• Claude Code Version: 2.0.71
• Platform: Kubeflow notebook pod (Linux), but affects all platforms
• Region: eu-central-1 (issue affects all non-US regions)
• Working Environment Variables:

ANTHROPIC_MODEL=global.anthropic.claude-sonnet-4-5-20250929-v1:0
CLAUDE_CODE_USE_BEDROCK=1
AWS_DEFAULT_REGION=eu-central-1

Root Cause Analysis:

Inspection of the Claude Code binary (v2.0.71) reveals hardcoded model IDs:

# From the minified Claude Code binary:
FUA = {
  firstParty: "claude-3-5-haiku-20241022",
  bedrock: "us.anthropic.claude-3-5-haiku-20241022-v1:0",  // ❌ Hardcoded old prefix
  vertex: "claude-3-5-haiku@20241022",
  foundry: "claude-3-5-haiku"
}

The main conversation model is configurable via ANTHROPIC_MODEL (allowing users to use global.), but sub-agent models use these hardcoded values with the deprecated us. prefix.

Why This Matters:

AWS Bedrock has migrated to cross-region model IDs using the global. prefix. The us. prefix is deprecated and causes failures in regions outside of us-east-1 and us-west-2.

This should be applied to all models including:

• Claude 3.5 Haiku
• Claude Haiku 4.5
• Claude Sonnet 4/4.5
• Claude Opus 4/4.1/4.5

Current Workaround:

Avoid using multi-agent features until fixed. Main conversation works fine.