/compact and auto-compact fail with 500 Internal Server Error on Opus 4.5

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

Both manual /compact and automatic compaction fail with a 500 Internal Server Error. The error persists across multiple attempts and has been occurring for at least 30+ minutes.

What Claude Actually Did

## Error Message

/compact
⎿ Error: Error during compaction: Error: API Error: 500 {"type":"error","error":{"type":"api_error","message":"Internal server error"},"request_id":null}

Expected Behavior

Compaction should succeed, reducing context size.

Files Affected

Permission Mode

Accept Edits was ON (auto-accepting changes)

Can You Reproduce This?

Yes, every time with the same prompt

Steps to Reproduce

1. Start a Claude Code session with Opus 4.5
2. Work until context grows large enough to trigger compaction
3. Run /compact manually OR wait for auto-compact to trigger
4. Observe 500 error

Claude Model

Opus

Relevant Conversation

Claude said: ● 4 agents completed! Let me check the remaining two (Speed Insights and Health endpoint):

● Task Output a7c8f33
  ⎿  Read output (ctrl+o to expand)

● Task Output a2fa313
  ⎿  Read output (ctrl+o to expand)
  ⎿  Context low · Run /compact to compact & continue

> /compact 
  ⎿  Error: Error during compaction: Error: API Error: 500 {"type":"error","error":{"type":"api_error","message":"Internal server error"},"request_id":null}

Impact

Low - Minor inconvenience

Claude Code Version

• Claude Code Version: 2.0.76

Platform

Anthropic API

Additional Context

• IDE: VS Code extension version 2.0.76 (server version: 2.0.75)
• Login Method: Claude Max Account
• OS: Linux
• MCP Servers: playwright, markitdown, context7, prisma, protocol-manager, seo-agent, mcp-pinecone, stripe, claude-in-chrome