Add Opus 4.6 as a selectable model in the VS Code extension

Summary

The VS Code extension currently exposes only three tiers in the model picker — opus / sonnet / haiku — with the opus tier pinned to 4.7. Opus 4.6 is not selectable from the extension.

Problem

4.6 and 4.7 have distinctly different voice and behavior, especially for non-code work:

• 4.7 prose (especially bilingual Chinese / English long-form writing) often reads as translation-inflected, with an "engineering tone" that's ill-suited to narrative articles, newsletters, or journal correspondence.
• 4.6 produces noticeably more natural, rhythmic Chinese prose and better English narrative voice.
• Many workflows mix the two intentionally: 4.6 for article writing / paper revision, 4.7 for coding and agentic work.

Currently the only way to use 4.6 is to drop out of the IDE and open a separate terminal with the CLI (claude --model claude-opus-4-6), which breaks flow and loses the editor integration. The CLI already supports --model claude-opus-4-6 cleanly, so the capability exists — it just isn't surfaced in the extension.

Request

Please add claude-opus-4-6 to the VS Code extension's model picker (either as a separate entry alongside opus/sonnet/haiku, or as a sub-option under the opus tier). At minimum, make it possible to configure a preferred opus version via extension settings so users who consistently prefer 4.6 for writing work don't have to switch to the CLI each time.

Use case

Bilingual Chinese / English technical writing:

• Center newsletter articles (1,000-2,000 word narrative pieces)
• Journal correspondence and manuscript revisions
• Teaching material drafts

For these, 4.6's voice is markedly preferable; for the surrounding coding / file-editing work in the same IDE session, 4.7 remains the right choice. Being able to toggle within the extension would remove the current terminal workaround.

Environment

• VS Code native Claude Code extension
• macOS (Darwin 25.3.0)
• Claude Code CLI (installed separately) does support --model claude-opus-4-6