claude-code - 💡(How to fix) Fix [BUG] Switching from Sonnet back to Opus after "prompt too long" error leaves session in broken state [1 participants]

After accidentally switching from Opus to Sonnet mid-session, Sonnet triggered a "Prompt is too long" error. Switching back to Opus did not recover the session — it remained broken. /compact was unavailable, and opening a new session did not resolve the issue. Switching back to Opus (which supports a larger context window) should clear the error state and allow the session to resume normally.

Error Messages/Logs

Sonnet returns "Prompt is too long" error (Sonnet has a smaller context window)

TL;DR

Switching to Sonnet and back to Opus mid-session may require a full session reset or a specific workaround to recover from the "Prompt is too long" error state.

Guidance

• Verify that the issue persists across different sessions and platforms to rule out environment-specific factors.
• Attempt to use the /reset command (if available) after switching back to Opus to clear the error state.
• Check the Claude Code documentation for any model-specific limitations or workarounds when switching between Opus and Sonnet.
• Consider filing a feature request to improve session recovery when switching between models with different context window sizes.

Example

No specific code snippet is applicable in this case, as the issue appears to be related to model switching and session state management.

Notes

The exact workaround or fix may depend on the internal implementation of Claude Code and the Anthropic API, which is not fully specified in the issue.

Recommendation

Apply workaround: Attempt to use the /reset command (if available) after switching back to Opus to clear the error state, as this may help recover the session without requiring a full restart.