Add shortcuts to step between sibling model tiers (Sol, Terra, Luna)

What variant of Codex are you using?

CLI

What feature would you like to see?

Codex CLI currently provides shortcuts for increasing or decreasing reasoning effort.

It would be useful to add equivalent, configurable actions for moving between sibling model tiers within the active model family.

For GPT-5.6, for example, the order would be:

Luna ↔ Terra ↔ Sol

Suggested behaviour

• Add previous_model_tier and next_model_tier actions to /keymap.
• Consider Alt+Shift+, for the lighter tier and Alt+Shift+. for the stronger tier, extending the existing reasoning-effort bindings without occupying the arrow keys.
• Restrict switching to sibling tiers within the same model family, rather than cycling through every available model.
• Preserve the current reasoning effort when the new tier supports it.
• When it is not supported, use the closest supported effort or the model tier’s default.
• Apply the change to the next turn and update the footer or status display immediately.
• When the active model has no sibling tiers, leave the selection unchanged and show a brief explanatory message.

Motivation

Sibiling tiers provide a lot more control over the ways tokens are spent. However, this flexibility requires shift tier as well as effort,

A direct shortcut would make it easy to move between Luna, Terra and Sol without opening /model.

Additional information

_No response_