[Bedrock] Subagents default to US region instead of inheriting EU region causing API Error

[kingkrausel]

Reproduce:

import asyncio
import tempfile
from claude_agent_sdk import AgentDefinition, ClaudeAgentOptions, ClaudeSDKClient
from .config import settings

async def run() -> None:

    simple_test_agent = AgentDefinition(
        description="Simple test agent. Ask it to greet you.",
        prompt=f"""You are a simple test agent. Just greet the caller.""",
        tools=[],
        model="sonnet",
    )

    env = {
            "CLAUDE_CODE_USE_BEDROCK": "1",
            "AWS_REGION": "eu-central-1",
            "AWS_ACCESS_KEY_ID": settings.AWS_ACCESS_KEY_ID,
            "AWS_SECRET_ACCESS_KEY": settings.AWS_SECRET_ACCESS_KEY.get_secret_value(),
        }

    

    with tempfile.TemporaryDirectory() as _temp_dir:
        options = ClaudeAgentOptions(
            agents={"simple-test-agent": simple_test_agent},
            model="eu.anthropic.claude-sonnet-4-5-20250929-v1:0" ,
            system_prompt="You are a simple test agent running on AWS Bedrock in the eu.",
            cwd=_temp_dir,
            env=env,
            allowed_tools=["Read", "Edit", "Write", "Grep", "Glob"],
            permission_mode="acceptEdits",
        )
        async with ClaudeSDKClient(options) as client:
            await client.query("Just ask the simple test agent to greet you.")
            async for message in client.receive_response():
                print(message)

if __name__ == "__main__":
    asyncio.run(run())

Error:

'API Error (us.anthropic.claude-sonnet-4-5-20250929-v1:0): 400 The provided model identifier is invalid.'

Complete output:

SystemMessage(subtype='init', data={'type': 'system', 'subtype': 'init', 'cwd': '/private/var/folders/_6/kdmc0m2x52l34v/T/tmp8yygaq0h', 'session_id': 'b22d2788-d6e8-468b-a936-e7414f1a351b', 'tools': ['Task', 'Bash', 'Glob', 'Grep', 'ExitPlanMode', 'Read', 'Edit', 'Write', 'NotebookEdit', 'WebFetch', 'TodoWrite', 'BashOutput', 'KillShell', 'Skill', 'SlashCommand'], 'mcp_servers': [], 'model': 'eu.anthropic.claude-sonnet-4-5-20250929-v1:0', 'permissionMode': 'acceptEdits', 'slash_commands': ['compact', 'context', 'cost', 'init', 'pr-comments', 'release-notes', 'todos', 'review', 'security-review'], 'apiKeySource': '/login managed key', 'claude_code_version': '2.0.32', 'output_style': 'default', 'agents': ['general-purpose', 'statusline-setup', 'Explore', 'Plan', 'simple-test-agent'], 'skills': [], 'plugins': [], 'uuid': '6c454d19-1c79-44d7-bbbf-33e4078aae4a'})
AssistantMessage(content=[TextBlock(text="I'll launch the simple test agent and ask it to greet me.")], model='claude-sonnet-4-5-20250929', parent_tool_use_id=None)
AssistantMessage(content=[ToolUseBlock(id='toolu_bdrk_01MHYaAGHMTdMQqtS9vXF6Q9', name='Task', input={'subagent_type': 'simple-test-agent', 'description': 'Request greeting from test agent', 'prompt': 'Please greet me!'})], model='claude-sonnet-4-5-20250929', parent_tool_use_id=None)
UserMessage(content=[TextBlock(text='Please greet me!')], parent_tool_use_id='toolu_bdrk_01MHYaAGHMTdMQqtS9vXF6Q9')
UserMessage(content=[ToolResultBlock(tool_use_id='toolu_bdrk_01MHYaAGHMTdMQqtS9vXF6Q9', content=[{'type': 'text', 'text': 'API Error (us.anthropic.claude-sonnet-4-5-20250929-v1:0): 400 The provided model identifier is invalid.'}], is_error=None)], parent_tool_use_id=None)
AssistantMessage(content=[TextBlock(text="It looks like there's a model configuration issue with the simple test agent. The agent is trying to use a model identifier that's not available in the current environment (AWS Bedrock EU region).\n\nThis appears to be a technical limitation - the simple test agent may be configured with a model that's not available in the eu region of AWS Bedrock where this instance is running.")], model='claude-sonnet-4-5-20250929', parent_tool_use_id=None)
ResultMessage(subtype='success', duration_ms=8748, duration_api_ms=8459, is_error=False, num_turns=2, session_id='b22d2788-d6e8-468b-a936-e7414f1a351b', total_cost_usd=0.002955, usage={'input_tokens': 10, 'cache_creation_input_tokens': 12591, 'cache_read_input_tokens': 12430, 'output_tokens': 197, 'server_tool_use': {'web_search_requests': 0, 'web_fetch_requests': 0}, 'service_tier': 'standard', 'cache_creation': {'ephemeral_1h_input_tokens': 0, 'ephemeral_5m_input_tokens': 0}}, result="It looks like there's a model configuration issue with the simple test agent. The agent is trying to use a model identifier that's not available in the current environment (AWS Bedrock EU region).\n\nThis appears to be a technical limitation - the simple test agent may be configured with a model that's not available in the eu region of AWS Bedrock where this instance is running.")

[kingkrausel]

Still broken in version 2.0.53

[kingkrausel]

Workaround: "ANTHROPIC_DEFAULT_SONNET_MODEL": "eu.anthropic.claude-sonnet-4-5-20250929-v1:0"