[BUG]

Bug Report: Claude Code Switching Models Without User Notification

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: <!-- Not specified in conversation -->
• Operating System: macOS (Darwin 24.6.0)
• Terminal: Claude Code CLI

Bug Description

Claude Code is silently switching between different model versions during a conversation without notifying the user. The model claims to be different versions (Claude 3.5 Sonnet and Claude 3 Opus) when the system prompt indicates otherwise (Sonnet 4 and Opus 4.1). This lack of transparency is concerning for users on paid plans who need consistent model behavior.

Steps to Reproduce

1. Start a conversation with Claude Code
2. Ask "What is your model version?"
3. Run /model command to switch models
4. Ask the same question again
5. Observe that the model reports different versions than what the system prompt indicates

Expected Behavior

• Model should transparently indicate which version is actually being used
• Model switches should be clearly communicated to the user
• System prompt should accurately reflect the actual model version
• Users should have control and visibility over model selection, especially on paid plans

Actual Behavior

• Model reports being "Claude 3.5 Sonnet (October 2024)" when system prompt says "Sonnet 4"
• Model reports being "Claude 3 Opus" when system prompt says "Opus 4.1"
• Model switching happens without clear user notification
• Inconsistency between reported model versions and system prompt information

Additional Context

• User is on MAX plan ($200/month)
• This lack of transparency affects work planning and expectations
• Users need to know which model they're using to understand capabilities and limitations
• Ethical concern: Users paying for premium service should have full transparency about model usage
• The discrepancy between system prompt claims (Sonnet 4, Opus 4.1) and actual models (Claude 3.5 Sonnet, Claude 3 Opus) is confusing

Impact

This issue affects:

1. Trust: Users cannot trust which model they're actually using
2. Work Planning: Different models have different capabilities; users need to know which one they're working with
3. Value for Money: Premium users paying $200/month deserve transparency about service delivery
4. Ethical Concerns: Silent model switching without notification is not transparent business practice

Requested Resolution

1. Fix system prompt to accurately reflect actual model versions
2. Provide clear notification when models are switched
3. Allow users to see and control which model version they're using
4. Ensure consistency between reported and actual model versions

<img width="2072" height="772" alt="Image" src="https://github.com/user-attachments/assets/46e3fd37-8192-4dad-8628-e420e14db598" />