[BUG] Claude Code stopped respecting model in agent altogether

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?

Earlier this month (I think starting end of february ~25-26, but can definitely confirm March 1) Claude Code stopped launching the subagents with model parameter by default.
I fixed this by specifying the agents that should be launched with their appropriate models via memory, and that worked until today.
Today Claude tells me, that the Agent model does not have model parameter anymore and launches subagents inheriting their parent model, (Opus, in my case) which is not what I want

What Should Happen?

Claude Code respects model field in agent description and launches agent with appropriate model

Error Messages/Logs

Why are agents running with opus and not sonnet?

⏺ You're right — my mistake. The Agent tool doesn't have a model parameter, so agents inherit the parent model. Since you switched to Opus, all agents have been running on Opus instead of their configured models
  (most should be Sonnet per the agent config).

  The memory note says to use the model parameter when launching via Task tool, but the Agent tool I'm using doesn't expose that option. I don't have a way to override the model per-agent with the current tool.

  Would you like to switch back to Sonnet (/model) so the remaining agents run on the cheaper model? The only agents that should be on Opus are qa-lead, product-manager, and software-architect — and those are all
  done for now.

❯ Why did the agent tool stop having model parameter?

⏺ I honestly don't know — the Agent tool schema I have access to only exposes description, prompt, subagent_type, run_in_background, resume, and isolation. No model parameter.

  This might be a regression in the current CLI version (2.1.70), or it could have been moved elsewhere. I'd suggest checking the changelog or reporting it at https://github.com/anthropics/claude-code/issues if this
   was a previously available parameter that disappeared

Steps to Reproduce

1. Create agent configuration with Sonnet model
2. Switch your root model to Opus
3. Tell Claude to launch the subagent
4. Investigate the logs and find out that the agent was launched with Opus

Claude Model

Not sure / Multiple models

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.70

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

This is a high-priority bug that seriously hinders me in my agentic workflows