Opus Plan Mode: Automatic Model Switching Failure

Bug Description
OPUS PLAN MODE MODEL SWITCHING BUG REPORT
==========================================

Date: 2025-01-19
Context: Testing of Claude Code's "Opus Plan Mode" automatic model switching functionality
Status: Bug confirmed

PROBLEM DESCRIPTION
-------------------
The "Opus Plan Mode" feature (option 4 in model selection) advertises automatic model switching with the description "Use Opus 4.1 in plan mode, Sonnet 4 otherwise." Testing shows this model switching functionality does not work.

EXPECTED BEHAVIOR
-----------------

• Opus 4.1 should be used during planning phases
• Sonnet 4 should be used for implementation tasks ("otherwise")
• Model should switch automatically based on task type

OBSERVED BEHAVIOR
-----------------

• Model remained on Opus 4.1 in all tested scenarios
• No instances of switching to Sonnet 4 were observed
• Manual model verification consistently showed: "claude-opus-4-1-20250805"

TESTING METHODOLOGY
-------------------
Multiple scenarios were tested to trigger the "otherwise" condition:

1. Coding Tasks: Direct code edits (test skipping, file modifications)

• Expected: Switch to Sonnet
• Observed: Remained on Opus

1. After Exiting Plan Mode: Performed implementation work after approval

• Expected: Switch to Sonnet for implementation
• Observed: Remained on Opus

1. File Operations: Various file read/write operations

• Expected: Switch to Sonnet for implementation tasks
• Observed: Remained on Opus

1. Extended Implementation Work: Multiple code edits in sequence

• Expected: Switch to Sonnet for sustained implementation
• Observed: Remained on Opus throughout

TEST TIMELINE
-------------

Phase 1: Initial Code Edit Test

• User request: "skip all of the tests in this file"
• Action: Modified test file to add .skip
• Model check: "what model are you now?" → "Claude Opus 4.1"
• Result: No switching to Sonnet for coding task

Phase 2: Plan Mode Exit Test

• Started in plan mode (shift+tab activated)
• Approved plan via ExitPlanMode tool
• Performed code edits on bug report document
• Model remained Opus despite being in "otherwise" state
• User observation: "we exited plan mode and made edits but stayed in Opus"

Phase 3: Extended Implementation Test

• Multiple file edits across session
• Various implementation tasks performed
• Consistent model verification showed Opus throughout
• User: "still haven't found any way to switch into Sonnet"

REPRODUCTION STEPS
------------------

1. Select "Opus Plan Mode" (option 4) via /model command
2. Perform any implementation task (code editing, file operations)
3. Check model with "what model are you now?"
4. Observe: Model remains "claude-opus-4-1-20250805"
5. Repeat with various task types - same result

IMPACT
------

• Users selecting this option expecting efficiency receive expensive Opus processing for all tasks
• "Sonnet 4 otherwise" specification is misleading
• No cost optimization benefit is delivered

TECHNICAL REFERENCES
--------------------

• Model selection interface shows: "Opus Plan Mode: Use Opus 4.1 in plan mode, Sonnet 4 otherwise"
• Multiple model identity checks: "claude-opus-4-1-20250805"
• /model command confirmations of "opusplan" active status

CONCLUSION
----------
The model switching mechanism in "Opus Plan Mode" is non-functional. The "Sonnet 4 otherwise" behavior does not occur in any tested scenario. Users receive Opus processing continuously regardless of task type.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 1.0.84
• Feedback ID: 252b8777-b87d-4c37-9b22-632dc4359b93

Errors

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