defaultModel setting in settings.json not honored — always starts as Opus

Bug Description

defaultModel: "sonnet" in ~/.claude/settings.json is not being honored. New sessions always start as Opus 4.6 despite the setting.

Steps to Reproduce

1. Set "defaultModel": "sonnet" in ~/.claude/settings.json
2. Start a new Claude Code session
3. Run /model to check the active model

Expected Behavior

Session should start with Sonnet as the default model.

Actual Behavior

Session starts with Opus 4.6. Running /model shows:

Kept model as Default (Opus 4.6 · Most capable for complex work)

Environment

• Claude Code v2.1.74
• macOS (Darwin 25.2.0)
• Claude Max plan
• Shell: zsh

Settings

~/.claude/settings.json contains:

{
  "defaultModel": "sonnet",
  ...
}

No model override exists in project-level settings (.claude/settings.local.json) or session-start hooks.

Investigation Done

• Verified no project-level defaultModel override
• Verified session-start hook (~/.claude/hooks/session-start.sh) does not touch model settings
• No /model command was run before observing the issue — the session launched directly into Opus

Hypothesis

Possible that the welcome screen / model selection is driven by the plan tier (Claude Max) rather than respecting the defaultModel setting.