The Error

Maximum concurrent sessions reached (5/5). Close an existing session.

The Fix

# List all active sessions
claude sessions list

# Close sessions you no longer need (by session ID)
claude sessions close <session-id>

# Or close all idle sessions at once
claude sessions close --idle

Why This Works

Each Claude Code session maintains an active connection and consumes API concurrency quota. The 5-session limit exists to prevent runaway costs and API abuse. Closing idle sessions (tabs you forgot about, terminals that finished their task) frees slots immediately without waiting for automatic timeout.

If That Doesn’t Work

# Force-kill orphaned Claude Code processes
ps aux | grep "claude-code" | grep -v grep
kill -9 <orphaned-pid>

# If sessions are stuck in a "closing" state, clear the session store
rm -rf ~/.config/claude-code/sessions/*.lock
# Then restart Claude Code

Orphaned processes occur when VS Code crashes or terminals are force-closed without graceful shutdown. These phantom sessions count against your limit until the server-side timeout (usually 5 minutes) expires.

Prevention

Add to your CLAUDE.md:

Close Claude Code sessions explicitly when done. Never leave idle sessions open across multiple terminals. Use a single session for sequential tasks rather than spawning parallel sessions for small operations.