[BUG] haiku subagent delegates to 3.5

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?

model: haiku on subagent definition delegates to haiku-3.5, not the recent model.

What Should Happen?

delegate to haiku-4.5

Error Messages/Logs

Steps to Reproduce

define sub agent with model: haiku

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.0.19

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Non-interactive/CI environment

Additional Information

still model: claude-haiku-4-5-20251001 seems work