Fixing Claude API 'Stream Interrupted: Connection Reset' Errors

Quick Fixes for Immediate Relief

Nothing kills a long-form AI generation faster than a connection reset. If your stream is dropping mid-sentence, try these adjustments first:

• Bump SDK Timeouts: Claude 3.5 Sonnet can take 30+ seconds to process complex prompts. The default 60s timeout isn't enough. Set it to at least 300s.
• Kill Proxy Buffering: If you use Nginx, it might be trying to save the stream into a buffer. This triggers a timeout when the buffer doesn't fill fast enough. Turn it off.
• Check Your VPN: Corporate firewalls like Zscaler or Palo Alto often terminate "idle" TCP connections that stay open without sending data for more than 30 seconds.
• Update the Library: Run pip install -U anthropic or npm install @anthropic-ai/sdk@latest to ensure you have the latest connection handling logic.

What is Actually Happening?

Think of a "connection reset" (ECONNRESET) as a sudden hang-up on a phone call. Unlike a standard timeout where the server tells you it's busy, a reset means the socket was closed without a proper handshake.

This error usually strikes during the "thinking" phase (Time to First Token). While Claude processes a massive prompt, the connection remains open but silent. Intermediate hardware—like a load balancer or firewall—sees this silence and assumes the connection is dead, abruptly cutting the line.

Fix 1: Adjusting SDK Client Timeouts

The Python and Node.js SDKs have conservative defaults. When generating a 4,000-token report, Claude might pause briefly between chunks, causing the client to give up too early.

Python SDK Implementation

from anthropic import Anthropic

# We recommend a 10-minute timeout for heavy technical writing tasks
client = Anthropic(
    api_key="your_api_key",
    timeout=600.0, 
)

with client.messages.stream(
    model="claude-3-5-sonnet-20240620",
    max_tokens=4096,
    messages=[{"role": "user", "content": "Write a 20-page technical manual for a nuclear reactor."}]
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

Node.js SDK Implementation

import Anthropic from '@anthropic-ai/sdk';

const anthropic = new Anthropic({
  apiKey: 'my_api_key',
  timeout: 600000, // 10 minutes in milliseconds
});

const stream = await anthropic.messages.create({
  max_tokens: 4096,
  messages: [{ role: 'user', content: 'Explain quantum field theory in excruciating detail' }],
  model: 'claude-3-5-sonnet-20240620',
  stream: true,
});

for await (const event of stream) {
  if (event.type === 'content_block_delta') {
    process.stdout.write(event.delta.text);
  }
}

Fix 2: Nginx and Reverse Proxy Tuning

If you route Claude requests through your own infrastructure, Nginx is likely the bottleneck. By default, Nginx waits 60 seconds (proxy_read_timeout) before closing a connection. It also buffers responses, which is the opposite of what you want for a stream.

Apply these settings to your Nginx location block:

location /api/claude/ {
    proxy_pass https://api.anthropic.com/;
    proxy_http_version 1.1;
    proxy_set_header Connection "";
    
    # Crucial: streaming fails if buffering is on
    proxy_buffering off;
    proxy_cache off;
    
    # Give Claude time to think
    proxy_read_timeout 600s;
    proxy_send_timeout 600s;
    
    # Keep the pipe open
    keepalive_timeout 600s;
}

Fix 3: Overcoming Aggressive Network Gear

In a corporate office, the connection reset often comes from Deep Packet Inspection (DPI) tools. These tools dislike long-running HTTPS connections that don't transmit data constantly.

• Test Outside the VPN: Switch to a mobile hotspot. If the error disappears, your corporate network is killing the stream.
• Lower the MTU: In Docker or certain VPNs, packets larger than 1500 bytes get fragmented. This can lead to dropped connections. Try setting your interface MTU to 1400 using sudo ifconfig eth0 mtu 1400.
• Force HTTP/1.1: Some older proxies struggle with HTTP/2 multiplexing for Server-Sent Events (SSE). Check if your environment allows forcing the protocol.

Fix 4: Building a Resilient Retry Loop

Network blips are a fact of life. Instead of letting your app crash, wrap your stream in a retry mechanism with exponential backoff. This waits 2 seconds, then 4, then 8 before giving up.

import time
from anthropic import Anthropic, APIConnectionError

client = Anthropic()

def get_claude_response(prompt, retries=3):
    for i in range(retries):
        try:
            with client.messages.stream(
                model="claude-3-5-sonnet-20240620",
                max_tokens=2048,
                messages=[{"role": "user", "content": prompt}]
            ) as stream:
                for text in stream.text_stream:
                    yield text
            return 
        except APIConnectionError as e:
            if i < retries - 1:
                time.sleep(2 ** i) 
                continue
            raise e

How to Verify the Fix

Don't just hope it works. Test it with these three steps:

• The Stress Test: Send a prompt like "Write 3000 words on the evolution of 18th-century architecture." If it finishes without a reset, your timeouts are solid.
• Inspect the Wire: Use tcpdump -i any port 443 to look for RST (Reset) packets. If they stop appearing after your Nginx changes, you've solved the configuration issue.
• Enable Verbose Logging: Set export ANTHROPIC_LOG=debug in your terminal. This reveals the exact millisecond the connection drops, helping you match it against your proxy logs.