Fix Anthropic API Streaming Interrupted

Written by Michael Lip · Solo founder of Zovo · $400K+ on Upwork · 100% JSS Join 50+ builders · More at zovo.one

The Error

Your streaming Claude API response stops mid-generation. You see an incomplete response, a connection error, or one of these messages:

APIConnectionError: Connection error

stream ended without message_stop event

APIStatusError: 529 overloaded

Quick Fix

Wrap your streaming call with retry logic and handle mid-stream disconnects:

import anthropic

client = anthropic.Anthropic()

with client.messages.stream(
    max_tokens=1024,
    messages=[{"role": "user", "content": "Hello"}],
    model="claude-sonnet-4-6",
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

The SDK’s .stream() method handles connection management and raises catchable exceptions on failure.

What’s Happening

Streaming uses Server-Sent Events (SSE) over a long-lived HTTP connection. Three conditions commonly cause mid-stream interruptions:

First, network instability or proxy timeouts. Corporate proxies, load balancers, and CDNs often have idle timeout settings shorter than the time it takes Claude to generate a long response. When no data flows for a period, the intermediary closes the connection.

Second, API overload. When the Anthropic API is under heavy load, it may return a 529 status code mid-stream. This is different from a pre-request 429 rate limit because it happens after the response has started flowing.

Third, client-side timeouts. The SDK has default timeout settings that may be too short for long-running generations, especially with large max_tokens values.

Step-by-Step Fix

Step 1: Use the SDK stream helper

The Python and TypeScript SDKs provide stream helpers that handle the SSE protocol correctly:

Python:

import anthropic

client = anthropic.Anthropic()

with client.messages.stream(
    max_tokens=4096,
    messages=[{"role": "user", "content": "Write a detailed analysis"}],
    model="claude-sonnet-4-6",
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)

TypeScript:

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

const client = new Anthropic();

await client.messages
  .stream({
    messages: [{ role: "user", content: "Write a detailed analysis" }],
    model: "claude-sonnet-4-6",
    max_tokens: 4096,
  })
  .on("text", (text) => {
    process.stdout.write(text);
  });

Step 2: Get the final message without handling events

For long-running requests, the SDKs let you use streaming under the hood while returning the complete Message object. This avoids HTTP timeouts on requests with large max_tokens:

import anthropic

client = anthropic.Anthropic()

# Uses streaming internally, returns complete message
with client.messages.stream(
    max_tokens=128000,
    messages=[{"role": "user", "content": "Write a comprehensive report"}],
    model="claude-sonnet-4-6",
) as stream:
    message = stream.get_final_message()
print(message.content[0].text)

Step 3: Configure client timeouts

Increase the SDK timeout for long generations:

client = anthropic.Anthropic(
    timeout=600.0  # 10 minutes
)

const client = new Anthropic({
  timeout: 600000, // 10 minutes in milliseconds
});

Step 4: Implement retry logic for disconnects

Build retry logic around your streaming calls:

import anthropic
import time

client = anthropic.Anthropic()
max_retries = 3

for attempt in range(max_retries):
    try:
        with client.messages.stream(
            max_tokens=4096,
            messages=[{"role": "user", "content": "Write a detailed analysis"}],
            model="claude-sonnet-4-6",
        ) as stream:
            collected_text = ""
            for text in stream.text_stream:
                collected_text += text
                print(text, end="", flush=True)
            break  # Success
    except anthropic.APIConnectionError:
        if attempt < max_retries - 1:
            time.sleep(2 ** attempt)
            continue
        raise

Step 5: Handle 529 overloaded errors

The 529 status means the API is temporarily overloaded. Implement exponential backoff:

except anthropic.APIStatusError as e:
    if e.status_code == 529:
        wait_time = 2 ** attempt
        print(f"\nAPI overloaded, retrying in {wait_time}s...")
        time.sleep(wait_time)
        continue
    raise

Prevention

Always use the SDK’s .stream() helper rather than implementing raw SSE parsing. The SDK handles ping events, connection management, and event deserialization.

For production applications, set explicit timeouts proportional to your expected generation length. A 128K max_tokens request needs more time than a 1K request.

Monitor for 529 errors in your logs. Frequent 529s indicate you should reduce concurrency or implement request queuing.

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