[BUG] HTTP connection leak - creates new connection per request instead of reusing

Bug Report: HTTP Connection Leak

What's Wrong?

Claude Code creates new TCP connections for each API request instead of reusing existing connections via HTTP keep-alive. This causes TIME_WAIT connection accumulation that scales with network timeout settings.

Measured behavior:

• With standard 120s TIME_WAIT timeout: ~1800 connections accumulated to api.anthropic.com
• Connections rapidly churn: 25 ESTABLISHED → 9 → 3 in 4 seconds after activity stops
• Each connection uses a unique port number (no connection reuse observed)
• Pattern: Create connection → Single request → Immediate close

What Should Happen?

Claude Code should use HTTP keep-alive with connection pooling, maintaining 2-10 persistent connections that are reused for multiple requests (standard Node.js HTTPS behavior).

Error Messages/Logs

Connection monitoring output:

=== Connection state over time ===
Sample 1: 25 ESTABLISHED
Sample 2 (2s later): 9 ESTABLISHED
Sample 3 (2s later): 3 ESTABLISHED

=== Total accumulation (120s TIME_WAIT) ===
1677 connections to api.anthropic.com
171 connections to statsig.anthropic.com

Port number analysis showing no reuse:

Ports at T=0s: 63912 64158 64159 64160 64161 64163 64164...
Ports at T=5s: 64186 64188
(All different ports = new connections, not reused)

Steps to Reproduce

1. Use Claude Code normally for 2-3 minutes (regular chat interaction)
2. Monitor TCP connections in another terminal:

``bash
netstat -an | grep api.anthropic.com | awk '{print $6}' | sort | uniq -c
``

1. Observe during activity:

• 10-25 ESTABLISHED connections active
• 200-1800+ TIME_WAIT connections (scales with network TIME_WAIT timeout)

1. Observe after activity stops:

• ESTABLISHED connections drop to 2-3 within seconds
• TIME_WAIT connections persist for timeout duration

1. Repeat monitoring every 2 seconds - observe different port numbers each time (proves no connection reuse)

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Claude Code Version

2.0.9 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Impact:

• Excessive connection table consumption on routers/firewalls
• Potential connection limit exhaustion
• May trigger automated alerts on network monitoring systems
• Affects users behind NAT with connection tracking

Current workaround:
Reduced TIME_WAIT timeout on router from 120s to 10s:

sysctl -w net.netfilter.nf_conntrack_tcp_timeout_time_wait=10

This reduces accumulation from ~1800 to ~150 connections, but only treats symptoms.

Root cause analysis:
Claude Code's HTTP client appears to be missing keep-alive configuration. Each API call creates a new TCP connection instead of reusing existing ones.

Expected fix:
Configure HTTPS agent with keep-alive:

const agent = new https.Agent({
  keepAlive: true,
  maxSockets: 10,
  keepAliveMsecs: 30000
});

Testing notes:

• Tested through both rule-based and global proxy modes - identical behavior
• Confirms issue is Claude Code's HTTP client configuration