[FEATURE] Create a 'fableplan' alias akin to opusplan

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Opusplan is really convenient to be able to use Opus for the complex planning work and Sonnet for the grunt work of implementation. Currently, there is no analogous alias for Fable.

Proposed Solution

Create a similar alias for Fable, to use Fable for the planning work and Sonnet for the implementation. It could be called fableplan to be similar to opusplan.

So I should be able to set fableplan in /model and have Claude Code use Fable for planning and Sonnet for implementation.

Alternative Solutions

I can override ANTHROPIC_DEFAULT_OPUS_MODEL to use Fable, so then the existing opusplan alias will use Fable instead of Opus for planning.

But this override means Opus will be replaced everywhere, even if I am using it for other things.

I can switch between the models manually but this is annoying and requires human intervention.

Priority

Medium - Would be very helpful

Feature Category

Configuration and settings

Use Case Example

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Additional Context

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export ANTHROPIC_DEFAULT_OPUS_MODEL="arn:aws:bedrock:<region>:<account>:application-inference-profile/<fable-5-profile-id>"
export ANTHROPIC_DEFAULT_SONNET_MODEL="arn:aws:bedrock:<region>:<account>:application-inference-profile/<sonnet-profile-id>"