Subagent model IDs use hyphen notation (claude-sonnet-4-6) instead of dot notation (claude-sonnet-4.6)

Bug Report

Description

When spawning subagents using the Agent tool with model: "sonnet", Claude Code internally resolves the model to claude-sonnet-4-6 (using hyphens). However, some API deployments require the dot notation claude-sonnet-4.6.

Error

API Error: 400 {"error":{"message":"400: Invalid model name passed in model=claude-sonnet-4-6. Call /v1/models to view available models for your key."}}

Expected Behavior

The model shorthand "sonnet" should resolve to claude-sonnet-4.6 (dot notation), or Claude Code should respect the ANTHROPIC_MODEL environment variable when resolving subagent model IDs.

Actual Behavior

The model shorthand "sonnet" resolves to claude-sonnet-4-6 (hyphen notation), which is rejected by some API deployments.

Workaround

None currently available. The ANTHROPIC_MODEL env var in settings.json only affects the main model, not subagents spawned via the Agent tool.

Environment

• Platform: macOS
• Shell: zsh