[BUG] Subagent tasks set and billed to Sonnet-5 despite Haiku set as session model (v2.1.198)

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?

Subagents execute using a different model (Sonnet) from the parent model (Haiku) that was selected in the Claude CLI.

What Should Happen?

All work under this API key/session should bill to Haiku (parent model), per explicit
model selection.

Error Messages/Logs

Steps to Reproduce

1. Run /model and select Haiku 4.5
2. Use Claude Code normally (file reads, small code edits) — allow it to

delegate to built-in subagents (Explore/general-purpose) as it sees fit

1. Check Console usage dashboard grouped by Model for that day

Claude Model

Other

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.198

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

• Current workaround is to place export CLAUDE_CODE_SUBAGENT_MODEL="haiku" inside of ~/.zshrc
• Model is Haiku 4.5 (Set on June 29th and still active via /model on July 2nd)
• No custom agents (~/.claude/agents/ and .claude/agents/ both empty)
• Reproduces in both macOS terminal and Mac VSCode terminal

<img width="875" height="765" alt="Image" src="https://github.com/user-attachments/assets/1c8e9caa-e59c-4eb8-a18e-bc1d59bac061" />