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Async Support

HTTPX offers a standard synchronous API by default, but also gives you the option of an async client if you need it.

Async is a concurrency model that is far more efficient than multi-threading, and can provide significant performance benefits and enable the use of long-lived network connections such as WebSockets.

If you're working with an async web framework then you'll also want to use an async client for sending outgoing HTTP requests.

Making Async requests

To make asynchronous requests, you'll need an AsyncClient.

>>> async with httpx.AsyncClient() as client:
...     r = await client.get('')
>>> r
<Response [200 OK]>


Use IPython or Python 3.8+ with python -m asyncio to try this code interactively, as they support executing async/await expressions in the console.

API Differences

If you're using an async client then there are a few bits of API that use async methods.

Making requests

The request methods are all async, so you should use response = await client.get(...) style for all of the following:

  • AsyncClient.get(url, ...)
  • AsyncClient.options(url, ...)
  • AsyncClient.head(url, ...)
  •, ...)
  • AsyncClient.put(url, ...)
  • AsyncClient.patch(url, ...)
  • AsyncClient.delete(url, ...)
  • AsyncClient.request(method, url, ...)
  • AsyncClient.send(request, ...)

Opening and closing clients

Use async with httpx.AsyncClient() if you want a context-managed client...

async with httpx.AsyncClient() as client:


In order to get the most benefit from connection pooling, make sure you're not instantiating multiple client instances - for example by using async with inside a "hot loop". This can be achieved either by having a single scoped client that's passed throughout wherever it's needed, or by having a single global client instance.

Alternatively, use await client.aclose() if you want to close a client explicitly:

client = httpx.AsyncClient()
await client.aclose()

Streaming responses

The, url, ...) method is an async context block.

>>> client = httpx.AsyncClient()
>>> async with'GET', '') as response:
...     async for chunk in response.aiter_bytes():
...         ...

The async response streaming methods are:

  • Response.aread() - For conditionally reading a response inside a stream block.
  • Response.aiter_bytes() - For streaming the response content as bytes.
  • Response.aiter_text() - For streaming the response content as text.
  • Response.aiter_lines() - For streaming the response content as lines of text.
  • Response.aiter_raw() - For streaming the raw response bytes, without applying content decoding.
  • Response.aclose() - For closing the response. You don't usually need this, since .stream block closes the response automatically on exit.

For situations when context block usage is not practical, it is possible to enter "manual mode" by sending a Request instance using client.send(..., stream=True).

Example in the context of forwarding the response to a streaming web endpoint with Starlette:

import httpx
from starlette.background import BackgroundTask
from starlette.responses import StreamingResponse

client = httpx.AsyncClient()

async def home(request):
    req = client.build_request("GET", "")
    r = await client.send(req, stream=True)
    return StreamingResponse(r.aiter_text(), background=BackgroundTask(r.aclose))


When using this "manual streaming mode", it is your duty as a developer to make sure that Response.aclose() is called eventually. Failing to do so would leave connections open, most likely resulting in resource leaks down the line.

Streaming requests

When sending a streaming request body with an AsyncClient instance, you should use an async bytes generator instead of a bytes generator:

async def upload_bytes():
    ...  # yield byte content

await, content=upload_bytes())

Explicit transport instances

When instantiating a transport instance directly, you need to use httpx.AsyncHTTPTransport.

For instance:

>>> import httpx
>>> transport = httpx.AsyncHTTPTransport(retries=1)
>>> async with httpx.AsyncClient(transport=transport) as client:
>>>     ...

Supported async environments

HTTPX supports either asyncio or trio as an async environment.

It will auto-detect which of those two to use as the backend for socket operations and concurrency primitives.


AsyncIO is Python's built-in library for writing concurrent code with the async/await syntax.

import asyncio
import httpx

async def main():
    async with httpx.AsyncClient() as client:
        response = await client.get('')


Trio is an alternative async library, designed around the the principles of structured concurrency.

import httpx
import trio

async def main():
    async with httpx.AsyncClient() as client:
        response = await client.get('')


The trio package must be installed to use the Trio backend.


AnyIO is an asynchronous networking and concurrency library that works on top of either asyncio or trio. It blends in with native libraries of your chosen backend (defaults to asyncio).

import httpx
import anyio

async def main():
    async with httpx.AsyncClient() as client:
        response = await client.get('')
        print(response), backend='trio')

Calling into Python Web Apps

For details on calling directly into ASGI applications, see the ASGITransport docs.