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openrouter-streaming-setup Implement streaming responses with OpenRouter for real-time UIs. Use when building chat interfaces, reducing time-to-first-token, or processing long completions. Triggers: 'openrouter streaming', 'openrouter sse', 'stream response openrouter', 'real-time openrouter'.
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langchain-deploy-integration Deploy a LangChain 1.0 / LangGraph 1.0 app to Cloud Run, Vercel, or LangServe correctly — with timeouts sized for chain length, cold-start mitigation, SSE anti-buffering headers, and Secret Manager over .env. Use when prepping a first production deploy, debugging a stream that hangs behind a proxy, or diagnosing p99 latency spikes. Trigger with "langchain deploy", "langchain cloud run", "langchain vercel python", "langchain langserve", or "langchain docker".
name openrouter-streaming-setup description Implement streaming responses with OpenRouter for real-time UIs. Use when building chat interfaces, reducing time-to-first-token, or processing long completions. Triggers: 'openrouter streaming', 'openrouter sse', 'stream response openrouter', 'real-time openrouter'.
allowed-tools Read, Write, Edit, Grep, Bash(python3:*), Bash(node:*) version 1.20.0 license MIT author Jeremy Longshore <jeremy@intentsolutions.io> tags ["saas","openrouter","streaming","real-time"] compatibility Designed for Claude Code
OpenRouter Streaming Setup
Overview
OpenRouter supports Server-Sent Events (SSE) streaming via stream: true, compatible with the OpenAI SDK. Streaming returns tokens as they're generated, reducing time-to-first-token (TTFT) from seconds to milliseconds. Usage stats are available via stream_options: {include_usage: true} in the final chunk. This skill covers Python and TypeScript streaming, SSE forwarding to browsers, and error recovery.
Prerequisites
An OpenRouter API key (sk-or-v1-...) exported as OPENROUTER_API_KEY — see the openrouter-install-auth skill for setup
Python 3.8+ or Node.js 18+ with the OpenAI SDK (the async example uses AsyncOpenAI from the same Python package)
FastAPI if you plan to forward the SSE stream to browsers per the SSE Forwarding section
A streaming-appropriate client timeout (e.g. 120s) — longer than for non-streaming requests
Instructions
Start with Python: Basic Streaming — pass stream=True plus stream_options={"include_usage": True} so the final chunk carries token counts, and print each chunk.choices[0].delta.content as it arrives.
Wrap that loop in the Python: Streaming with Metrics generator to capture TTFT and total time per request; the metrics dict is available after the generator is exhausted.
For Node services, use the TypeScript: Streaming for await loop over the same stream: true request.
To reach a browser UI, expose the FastAPI endpoint in SSE Forwarding to Browser — it re-emits each token as a data: {"token": ...} SSE line and terminates with data: [DONE].
Consume that endpoint with the Browser Client (JavaScript) reader loop, appending tokens to the DOM as they decode.
In async web frameworks, switch to the Async Streaming pattern built on AsyncOpenAI.
Handle mid-stream failures (cut-offs, missing usage, keep-alive pings, finish_reason: "length") per the Error Handling table.
Python: Basic Streaming
import os
from openai import OpenAI
client = OpenAI(
base_url="https://openrouter.ai/api/v1" ,
api_key=os.environ["OPENROUTER_API_KEY" ],
default_headers={"HTTP-Referer"
"https://my-app.com"
"X-Title"
"my-app"
"anthropic/claude-3.5-sonnet"
"role"
"user"
"content"
"Explain how HTTP streaming works"
500
True
"include_usage"
True
for
in
if
and
0
0
print
""
True
if
print
f"\n---\nTokens: {chunk.usage.prompt_tokens} in + {chunk.usage.completion_tokens} out"
""
Python: Streaming with Metrics import time
def stream_with_metrics (messages, model="anthropic/claude-3.5-sonnet" , **kwargs ):
"""Stream response and capture performance metrics."""
start = time.monotonic()
first_token_time = None
chunks = []
usage = None
stream = client.chat.completions.create(
model=model, messages=messages, stream=True ,
stream_options={"include_usage" : True },
**kwargs,
)
for chunk in stream:
if chunk.choices and chunk.choices[0 ].delta.content:
token = chunk.choices[0 ].delta.content
if first_token_time is None :
first_token_time = (time.monotonic() - start) * 1000
chunks.append(token)
yield token
if chunk.usage:
usage = {
"prompt_tokens" : chunk.usage.prompt_tokens,
"completion_tokens" : chunk.usage.completion_tokens,
}
total_time = (time.monotonic() - start) * 1000
stream_with_metrics.last_metrics = {
"ttft_ms" : round (first_token_time or 0 ),
"total_ms" : round (total_time),
"usage" : usage,
"model" : model,
}
for token in stream_with_metrics(
[{"role" : "user" , "content" : "Hello" }],
model="openai/gpt-4o-mini" ,
max_tokens=200 ,
):
print (token, end="" , flush=True )
print (f"\nMetrics: {stream_with_metrics.last_metrics} " )
TypeScript: Streaming import OpenAI from "openai" ;
const client = new OpenAI ({
baseURL : "https://openrouter.ai/api/v1" ,
apiKey : process.env .OPENROUTER_API_KEY ,
defaultHeaders : { "HTTP-Referer" : "https://my-app.com" , "X-Title" : "my-app" },
});
async function streamCompletion (prompt : string , model = "openai/gpt-4o-mini" const stream = await client.chat .completions .create ({
model,
messages : [{ role : "user" , content : prompt }],
max_tokens : 500 ,
stream : true ,
});
const chunks : string [] = [];
for await (const chunk of stream) {
const token = chunk.choices [0 ]?.delta ?.content ;
if (token) {
process.stdout .write (token);
chunks.push (token);
}
}
return chunks.join ("" );
}
SSE Forwarding to Browser (FastAPI) from fastapi import FastAPI
from fastapi.responses import StreamingResponse
app = FastAPI()
@app.post("/v1/stream"
async def stream_endpoint (prompt: str , model: str = "openai/gpt-4o-mini" ):
"""Forward OpenRouter SSE stream to browser."""
async def generate ():
stream = client.chat.completions.create(
model=model,
messages=[{"role" : "user" , "content" : prompt}],
max_tokens=1024 ,
stream=True ,
)
for chunk in stream:
if chunk.choices and chunk.choices[0 ].delta.content:
token = chunk.choices[0 ].delta.content
yield f"data: {json.dumps({'token' : token} )}\n\n"
yield "data: [DONE]\n\n"
return StreamingResponse(generate(), media_type="text/event-stream" )
Browser Client (JavaScript)
async function streamChat (prompt ) {
const response = await fetch ("/v1/stream" , {
method : "POST" ,
headers : { "Content-Type" : "application/json" },
body : JSON .stringify ({ prompt }),
});
const reader = response.body .getReader ();
const decoder = new TextDecoder ();
while (true ) {
const { done, value } = await reader.read ();
if (done) break ;
const text = decoder.decode (value);
for (const line of text.split ("\n" )) {
if (line.startsWith ("data: " ) && line !== "data: [DONE]" ) {
const data = JSON .parse (line.slice (6 ));
document .getElementById ("output" ).textContent += data.token ;
}
}
}
}
Async Streaming (Python) from openai import AsyncOpenAI
aclient = AsyncOpenAI(
base_url="https://openrouter.ai/api/v1" ,
api_key=os.environ["OPENROUTER_API_KEY" ],
default_headers={"HTTP-Referer" : "https://my-app.com" , "X-Title" : "my-app" },
)
async def async_stream (messages, model="openai/gpt-4o-mini" , **kwargs ):
"""Async streaming for use in async web frameworks."""
stream = await aclient.chat.completions.create(
model=model, messages=messages, stream=True , **kwargs,
)
async for chunk in stream:
if chunk.choices and chunk.choices[0 ].delta.content:
yield chunk.choices[0 ].delta.content
Output
Token-by-token console output as the model generates, followed by usage counts from the final chunk (Tokens: 14 in + 132 out)
A metrics dict after the generator is exhausted: ttft_ms, total_ms, usage token counts, and the model used
A FastAPI SSE endpoint emitting data: {"token": ...} lines and a terminating data: [DONE] for browser consumption
Incrementally rendered text in the browser as the JavaScript reader loop decodes each SSE line
Examples Stream with metrics and inspect TTFT after the tokens finish printing:
for token in stream_with_metrics(
[{"role" : "user" , "content" : "Write a haiku about programming" }],
model="openai/gpt-4o-mini" , max_tokens=60 ,
):
print (token, end="" , flush=True )
print (f"\nMetrics: {stream_with_metrics.last_metrics} " )
More worked examples: references/examples.md.
Error Handling Error Cause Fix Stream cuts off mid-response Network timeout or provider error Save partial content; implement retry from last position Missing usage in stream Didn't set stream_options Add stream_options: {"include_usage": True} Empty delta chunks Keep-alive pings Filter chunk.choices[0].delta.content is None finish_reason: "length"Hit max_tokens limit Increase max_tokens or continue with follow-up request
Enterprise Considerations
Always use stream_options: {"include_usage": True} to get token counts for cost tracking
Set connection timeouts appropriate for streaming (longer than non-streaming, e.g., 120s)
Implement heartbeat detection: if no chunks for >30s, consider the stream dead and retry
Buffer partial tokens on the server before forwarding to the client for smoother rendering
Log TTFT per model to benchmark streaming performance over time
Use streaming for all user-facing requests; use non-streaming for batch/background processing
References 