[FEATURE] Allow combined Sonnet/Haiku usage similarly 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

With the introduction of Haiku 4.5 it would be viable to use that for doing code changes based on planning executed by Sonnet. This currently requires manually switching between models, which is an extra step, can be forgotten, etc.

Proposed Solution

Introduce a new mode similar to what we had with opusplan, e.g. claude --model sonnetplan which would dynamically use Sonnet for planning and Haiku for editing

Alternative Solutions

A seemingly feasible workaround would be to override the default models via the env variables and switch to opusmode, but that's not available on the pro plan.

myUser@myMachine myFolder % export ANTHROPIC_DEFAULT_OPUS_MODEL=claude-sonnet-4-5
myUser@myMachine myFolder % export ANTHROPIC_DEFAULT_SONNET_MODEL=claude-haiku-4-5
myUser@myMachine myFolder % claude --model opusplan
Claude Pro users are not currently able to use Opus in Claude Code. The current model is now Sonnet.

Priority

Medium - Would be very helpful

Feature Category

CLI commands and flags

Use Case Example

_No response_

Additional Context

_No response_