Workflow agent() model option ignored on AWS Bedrock — always falls back to Haiku

Summary

When using the Workflow tool with agent() calls that include the model: option, the specified model is completely ignored on AWS Bedrock backends. Agents always run on Haiku regardless of what model is passed.

Environment

• CLAUDE_CODE_USE_BEDROCK=1
• AWS_REGION=eu-west-1
• Session model: opusplan (Bedrock alias)
• CLAUDE_CODE_SUBAGENT_MODEL=eu.anthropic.claude-opus-4-8-20251101-v1:0

Steps to reproduce

1. Configure Claude Code to use AWS Bedrock (CLAUDE_CODE_USE_BEDROCK=1)
2. Write a workflow script with an agent() call that includes model: option:

``js
await agent("do something", { model: "eu.anthropic.claude-opus-4-8-20251101-v1:0" })
``

1. Launch the workflow
2. Observe the agent label in the /workflows UI — it shows Haiku, not Opus

What was tried

All of the following model: values were tested — all resulted in Haiku:

• "opus"
• "claude-opus-4-8"
• "eu.anthropic.claude-opus-4-8-20251101-v1:0" (exact Bedrock cross-region inference profile ID from settings)

Note: CLAUDE_CODE_SUBAGENT_MODEL env var correctly overrides the model for Agent tool subagents, but has no effect on Workflow agent() calls.

Expected behavior

agent() calls with model: option should respect the specified model and route to the correct Bedrock model ID.

Impact

Workflow agent() calls cannot be routed to Opus on Bedrock environments, making it impossible to use more capable models for complex implementation tasks in workflows.