HTTPX vs aiohttp for Async API Requests in Python: Which One Should You Use

Python has two dominant libraries for making async HTTP requests: httpx and aiohttp. Both work with asyncio, both support connection pooling, and both can fire off hundreds of concurrent requests without breaking a sweat. But they are built on different philosophies, ship with different feature sets, and shine in different situations. This article puts them side by side so you can make an informed choice for your next project.

By the end you will understand the core differences in API design, see both libraries handle the same real-world task, review performance characteristics, and have a clear decision framework for picking the right tool.

The Two-Sentence Version

If you are already using the requests library and want to add async support with minimal code changes, choose httpx. If you are building a high-concurrency async application from scratch and raw throughput is a priority, choose aiohttp.

That is the short answer. The rest of this article explains why.

Syntax Comparison: The Same Task, Two Libraries

The best way to see how these libraries differ is to watch them do the same job. Here is a function that fetches JSON from three API endpoints concurrently and returns the results.

HTTPX version

import asyncio
import httpx

async def fetch_json(client, url):
    response = await client.get(url)
    response.raise_for_status()
    return response.json()

async def main():
    urls = [
        "https://jsonplaceholder.typicode.com/users/1",
        "https://jsonplaceholder.typicode.com/users/2",
        "https://jsonplaceholder.typicode.com/users/3",
    ]
    async with httpx.AsyncClient() as client:
        tasks = [fetch_json(client, url) for url in urls]
        results = await asyncio.gather(*tasks)

    for user in results:
        print(user["name"])

asyncio.run(main())

aiohttp version

import asyncio
import aiohttp

async def fetch_json(session, url):
    async with session.get(url) as response:
        response.raise_for_status()
        return await response.json()

async def main():
    urls = [
        "https://jsonplaceholder.typicode.com/users/1",
        "https://jsonplaceholder.typicode.com/users/2",
        "https://jsonplaceholder.typicode.com/users/3",
    ]
    async with aiohttp.ClientSession() as session:
        tasks = [fetch_json(session, url) for url in urls]
        results = await asyncio.gather(*tasks)

    for user in results:
        print(user["name"])

asyncio.run(main())

At first glance the two versions look almost identical. The structural pattern -- create a session, build a list of tasks, pass them to asyncio.gather -- is the same. The differences are in the details.

With HTTPX, the response object gives you .json() as a regular method call. With aiohttp, reading the response body is itself an async operation, so you write await response.json(). This is because aiohttp uses a streaming response model where the body is not loaded into memory until you explicitly read it. HTTPX loads the response eagerly by default.

The other notable difference is the async with session.get(url) as response: pattern in aiohttp. Each individual request is a context manager that releases the connection back to the pool when the block exits. HTTPX does not require this -- the connection is managed internally by the client.

Feature-by-Feature Comparison

Performance: Where aiohttp Pulls Ahead

When raw async throughput is the primary metric, aiohttp tends to outperform HTTPX. This is not surprising: aiohttp was built from the ground up as an async-only library, and it uses compiled C extensions (via multidict, yarl, and aiohttp's own speedups module) to minimize overhead per request. HTTPX supports both synchronous and asynchronous operation, which requires an additional transport abstraction layer that adds a small amount of latency per request.

In practical terms, the difference becomes visible when you are sending hundreds or thousands of concurrent requests. For a typical application making 10-50 concurrent API calls, the performance gap is negligible. For a high-throughput web scraper processing thousands of pages, or a service that fans out requests to dozens of microservices, aiohttp's lower per-request overhead can add up.

HTTP/2 Support: Where HTTPX Wins

HTTP/2 allows multiple requests to be multiplexed over a single TCP connection, eliminates head-of-line blocking at the HTTP layer, and supports header compression. If you are communicating with a modern API server that supports HTTP/2, you can see meaningful improvements in latency and connection efficiency.

HTTPX supports HTTP/2 natively. You enable it by installing the optional dependency and passing http2=True to the client:

# Install with HTTP/2 support
# pip install httpx[http2]

import asyncio
import httpx

async def main():
    async with httpx.AsyncClient(http2=True) as client:
        response = await client.get("https://http2.pro/api/v1")
        data = response.json()
        print(f"Protocol: {response.http_version}")  # HTTP/2
        print(f"Response: {data}")

asyncio.run(main())

aiohttp does not support HTTP/2. If you need to make requests over HTTP/2 from an async Python application, HTTPX is your only mainstream option among the two.

Migrating from requests: Why HTTPX Makes It Easy

A large portion of Python developers start with the requests library for HTTP calls. When the time comes to add async support, HTTPX provides the smoothest migration path because its synchronous API mirrors requests almost exactly.

Here is the same GET request written three ways:

# Using requests (synchronous)
import requests

response = requests.get("https://api.example.com/data")
data = response.json()
print(response.status_code)

# Using httpx (synchronous -- drop-in replacement)
import httpx

response = httpx.get("https://api.example.com/data")
data = response.json()
print(response.status_code)

# Using httpx (async -- same API, different client)
import asyncio
import httpx

async def main():
    async with httpx.AsyncClient() as client:
        response = await client.get("https://api.example.com/data")
        data = response.json()
        print(response.status_code)

asyncio.run(main())

The sync HTTPX version is a one-line import change from requests. The async version wraps the same call in await and uses AsyncClient instead of the module-level function. The method names, response object attributes, and error handling all stay the same. This incremental migration path is one of the strongest arguments for choosing HTTPX if your codebase already uses requests.

With aiohttp, the migration requires learning a new API: ClientSession instead of Session, double context managers for each request, and await on response body methods. It is not difficult, but it is a larger surface area of change.

When to Choose Which Library

Choose HTTPX when...

Your project already uses requests and you want to incrementally adopt async without rewriting your HTTP layer. HTTPX's dual sync/async API means you can migrate one function at a time. It is also the clear choice if you need HTTP/2 support, or if your codebase has a mix of synchronous and asynchronous code paths that both need to make HTTP calls.

Choose aiohttp when...

You are building an async-first application from scratch and throughput is critical. aiohttp's async-only design means less abstraction overhead, and its compiled C extensions give it an edge in high-concurrency benchmarks. It is also the right pick if you need WebSocket support or a built-in async web server alongside your HTTP client code -- aiohttp handles both the client and server sides of HTTP.

Either library works well when...

You are making a moderate number of concurrent API calls (under 100) and your primary concern is code clarity rather than squeezing out the last millisecond of performance. In this range, both libraries will complete your requests in roughly the same wall-clock time. Pick whichever API you find more readable.

Key Takeaways

1. HTTPX offers sync and async in one package: You can use httpx.Client for synchronous code and httpx.AsyncClient for async code, both with the same API. This dual-mode design makes incremental migration from requests straightforward.
2. aiohttp is purpose-built for async and has a performance edge: Because it only supports asynchronous operation, aiohttp avoids the abstraction overhead of a dual-mode library. Compiled C extensions give it measurably better throughput in high-concurrency scenarios.
3. HTTP/2 is only available in HTTPX: If your API endpoints support HTTP/2 and you want to take advantage of multiplexing and header compression, HTTPX is the only mainstream async client that supports it.
4. aiohttp gives you both client and server: Beyond making HTTP requests, aiohttp can also serve as a full async web server with WebSocket support. HTTPX is strictly a client library.
5. For moderate workloads, the choice is about API preference: When you are making fewer than 100 concurrent requests, the performance difference between the two libraries is negligible. Choose based on which API you prefer to read and maintain.

Neither library is universally better than the other. They solve the same problem with different priorities. HTTPX optimizes for developer experience and migration ease. aiohttp optimizes for async-native performance and ecosystem breadth. Knowing where each one shines lets you pick the right tool without second-guessing the decision later.