[BUG] Task tool subagents don't inherit EU cross-region inference model configuration for AWS Bedrock

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 AWS Bedrock with EU cross-region inference models (model ID format: eu.anthropic.claude-sonnet-4-5-20250929-v1:0), the Task tool fails to launch subagents because it attempts to use the standard US model ID format
(anthropic.claude-sonnet-4-5-20250929-v1:0) instead of inheriting the configured EU model ID.

This results in a 403 authentication error because the AWS IAM role has access to the EU cross-region model but not the US format model.

What Should Happen?

The Task tool should inherit the configured model ID (eu.anthropic.claude-sonnet-4-5-20250929-v1:0) and successfully launch subagents using the same model configuration as the main conversation.

Error Messages/Logs

API Error: 403 {"Message":"User: arn:aws:sts::xxxxx:assumed-role/xxxxx/xxxxx@xxxxxx.se is
not authorized to perform: bedrock:InvokeModel on resource: arn:aws:bedrock:::foundation-model/anthropic.claude-sonnet-4-5-20250929-v1:0 with an
explicit deny in a service control policy"} · Please run /login

Steps to Reproduce

1. Configure Claude Code to use AWS Bedrock in eu-central-1 region
2. Set model to: eu.anthropic.claude-sonnet-4-5-20250929-v1:0 (EU cross-region inference format)
3. Verify main conversation works (it does, I can interact normally)
4. Attempt to launch a subagent using the Task tool with any subagent_type (e.g., general-purpose, Explore)
5. Observe the 403 error

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.37 (Claude Code)

Platform

AWS Bedrock

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_