[Feature Request] Auto-enable /fast at session start via fastMode: true setting on Opus 4.7 [1M]

Summary

When the base model is opus[1m] (Opus 4.7 with 1M context) and settings.json contains "fastMode": true, the setting is not applied at session start. The user must manually type /fast on every new session to switch rendering to Opus 5 speed. This is inconvenient in workflows that repeatedly spawn short-lived Claude Code tabs (e.g., Orca-based multi-CLI orchestration).

According to the runtime hint shown in the system prompt:

"Fast mode for Claude Code uses Claude Opus with faster output (it does not downgrade to a smaller model). It can be toggled with /fast and is available on Opus 5/4.8."

This implies auto-fast is intentionally scoped to Opus 5 / 4.8 only. For accounts where Opus 5/4.8 is not yet exposed, opus[1m] is the effective top tier, and fastMode: true is silently ignored at startup.

Environment

• Claude Code CLI: 2.1.229 (native, win32-x64)
• settings.json:

``json
{
"model": "opus[1m]",
"fastMode": true,
"effortLevel": "high",
"advisorModel": "fable"
}
``

• Session starts as: Opus 4.7 (1M context) (fast NOT active)
• After /fast on: Fast mode ON · model set to Opus 5 · $10/$50 per Mtok

Steps to reproduce

1. Set "model": "opus[1m]" and "fastMode": true in ~/.claude/settings.json.
2. Start a new Claude Code session.
3. Observe: model displays as Opus 4.7 (1M context). Fast mode is off. User must manually run /fast to activate.

Expected behavior

fastMode: true should auto-activate /fast at session start regardless of whether the base is Opus 4.7 [1M] or Opus 5/4.8 — since the user has already explicitly consented to the pricing implication by setting fastMode: true.

Alternative: if pricing-safety is the concern, add a distinct opt-in setting such as:

"fastModeOnLegacyOpus": true

that explicitly acknowledges the \$10/\$50 per Mtok tier and auto-applies on Opus 4.7 [1M].

Motivation

Multi-tab orchestration workflows (e.g., Orca-based 5-CLI systems that open multiple Claude tabs per task) repeatedly incur the /fast friction. Auto-application would remove this per-session manual step and match user intent already declared in settings.

Workarounds tried

• Setting fastMode: true → confirmed set in settings.json, silently ignored on Opus 4.7 [1M] startup.
• --fast CLI flag → does not exist in claude --help (v2.1.229).
• --startup-command-style flag → does not exist.
• SessionStart hook → cannot inject slash commands into the session.
• claude doctor → reports no installation issues.

Suggested fix

Honor fastMode: true at session start for any Opus model tier that supports /fast, not only Opus 5/4.8. Users who set this explicitly have already accepted the pricing.

Thank you for maintaining Claude Code.