The top-level `httpcore2.request()` function is provided for convenience. In practice whenever you're working with `httpcore2` you'll want to use the connection pooling functionality that it provides.
Once you're ready to get going, [head over to the documentation](https://github.com/pydantic/httpx2/tree/main/src/httpcore2/docs).
## Motivation
You *probably* don't want to be using HTTPCore 2 directly. It might make sense if
you're writing something like a proxy service in Python, and you just want
something at the lowest possible level, but more typically you'll want to use
a higher level client library, such as `httpx2`.
The motivation for `httpcore2` is:
* To provide a reusable low-level client library, that other packages can then build on top of.
* To provide a *really clear interface split* between the networking code and client logic,
so that each is easier to understand and reason about in isolation.
## Dependencies
The `httpcore2` package has the following dependencies...
* `h11`
* `truststore`
And the following optional extras...
* `anyio` - Required by `pip install 'httpcore2[asyncio]'`.
* `trio` - Required by `pip install 'httpcore2[trio]'`.
* `h2` - Required by `pip install 'httpcore2[http2]'`.
* `socksio` - Required by `pip install 'httpcore2[socks]'`.
## Versioning
We use [SEMVER for our versioning policy](https://semver.org/).
For changes between package versions please see our [project changelog](CHANGELOG.md).
We recommend pinning your requirements either the most current major version, or a more specific version range:
```shell
pip install 'httpcore2==2.*'
```
# Changelog
All notable changes to this project will be documented in this file.
The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
## 2.16.0 (October 21st, 2026)
No changes since `2.15.1`. Version bumped to stay in lockstep with `httpx2`.
## 2.15.1 (October 19th, 2026)
### Fixed
* Configure the default SSL context once on Linux, instead of on every handshake. With OpenSSL older than 3.4, CPU usage grew over the lifetime of a reused client.
* Add support for Python 3.15. ([#1090](https://github.com/pydantic/httpx2/pull/1090))
### Changed
* Avoid quadratic copying when sending large HTTP/2 request bodies. ([#1127](https://github.com/pydantic/httpx2/pull/1127))
### Fixed
* Propagate the original exception instead of raising `KeyError` when an HTTP/2 stream fails. ([#1093](https://github.com/pydantic/httpx2/pull/1093))
* Start TLS for the `wss` scheme in SOCKS5 proxy connections. ([#1104](https://github.com/pydantic/httpx2/pull/1104))
## 2.9.1 (July 24th, 2026)
No changes since `2.9.0`. Version bumped to stay in lockstep with `httpx2`.
## 2.9.0 (July 23rd, 2026)
No changes since `2.8.0`. Version bumped to stay in lockstep with `httpx2`.
## 2.8.0 (July 23rd, 2026)
### Changed
* Assign each released connection to a single queued request, eliminating multi-assignment churn in the connection pool. ([#1075](https://github.com/pydantic/httpx2/pull/1075))
## 2.7.0 (July 14th, 2026)
No changes since `2.6.0`. Version bumped to stay in lockstep with `httpx2`.
## 2.6.0 (July 14th, 2026)
### Fixed
* Clean up garbage connections on cancellation in `AsyncConnectionPool`. ([#983](https://github.com/pydantic/httpx2/pull/983))
* Read `_expire_at` only once in `has_expired()`. ([#1045](https://github.com/pydantic/httpx2/pull/1045))
## 2.5.0 (June 25th, 2026)
### Fixed
* Propagate the timeout through the SOCKS5 handshake. ([#1009](https://github.com/pydantic/httpx2/pull/1009))
* Release the HTTP/2 semaphore permit on `NoAvailableStreamIDError`. ([#1012](https://github.com/pydantic/httpx2/pull/1012))
* Use `RLock` instead of `Lock` to prevent a thread deadlock. ([#1008](https://github.com/pydantic/httpx2/pull/1008))
## 2.3.0 (June 1st, 2026)
### Changed
* Use `truststore` instead of `certifi` for default SSL verification, loading the operating system's trust store. ([#1002](https://github.com/pydantic/httpx2/pull/1002))
* Rewrite `_assign_requests_to_connections` as a single-pass loop. ([#974](https://github.com/pydantic/httpx2/pull/974))
* Use `anyio`'s `fast_acquire` for `Lock` and `Semaphore`. ([#970](https://github.com/pydantic/httpx2/pull/970))
* Use `memoryview` in `write()` to avoid copies. ([#954](https://github.com/pydantic/httpx2/pull/954))
## 2.2.0 (May 16th, 2026)
No changes since `2.1.0`. Version bumped to stay in lockstep with `httpx2`.
## 2.1.0 (May 15th, 2026)
### Removed
* Drop support for Python 3.8 and 3.9. ([#208](https://github.com/pydantic/httpx2/pull/208))
### Added
* Add support for Python 3.14. ([#208](https://github.com/pydantic/httpx2/pull/208))
* Bundle `LICENSE.md` in the sdist. ([#938](https://github.com/pydantic/httpx2/pull/938))
### Fixed
* Wait for positive flow-control credit when a peer's `SETTINGS` frame drives a stream's send window negative, instead of letting h2 raise `LocalProtocolError`. ([#935](https://github.com/pydantic/httpx2/pull/935))
## 2.0.0
Official first release of `httpcore2`. No changes since `2.0.0b1`.
## 2.0.0b1
First release of `httpcore2`, a fork of [`httpcore`](https://github.com/encode/httpcore) maintained by Pydantic. Forked from `httpcore 1.0.9`.
### Breaking changes
* **Renamed package**: `httpcore` -> `httpcore2`. `import httpcore` becomes `import httpcore2`. No other public API changed.
### Fixed
* Fix `max_keepalive_connections` not being properly handled. (Inherited from upstream PR [encode/httpcore#1000](https://github.com/encode/httpcore/pull/1000).)
---
Historical entries below are from upstream `encode/httpcore`.
## Version 1.0.9 (April 24th, 2025)
- Resolve https://github.com/advisories/GHSA-vqfr-h8mv-ghfj with h11 dependency update. (#1008)
## Version 1.0.8 (April 11th, 2025)
- Fix `AttributeError` when importing on Python 3.14. (#1005)
## Version 1.0.7 (November 15th, 2024)
- Support `proxy=…` configuration on `ConnectionPool()`. (#974)
## Version 1.0.6 (October 1st, 2024)
- Relax `trio` dependency pinning. (#956)
- Handle `trio` raising `NotImplementedError` on unsupported platforms. (#955)
- Handle mapping `ssl.SSLError` to `httpcore.ConnectError`. (#918)
## 1.0.5 (March 27th, 2024)
- Handle `EndOfStream` exception for anyio backend. (#899)
- Allow trio `0.25.*` series in package dependencies. (#903)
## 1.0.4 (February 21st, 2024)
- Add `target` request extension. (#888)
- Fix support for connection `Upgrade` and `CONNECT` when some data in the stream has been read. (#882)
## 1.0.3 (February 13th, 2024)
- Fix support for async cancellations. (#880)
- Fix trace extension when used with socks proxy. (#849)
- Fix SSL context for connections using the "wss" scheme (#869)
## 1.0.2 (November 10th, 2023)
- Fix `float("inf")` timeouts in `Event.wait` function. (#846)
## 1.0.1 (November 3rd, 2023)
- Fix pool timeout to account for the total time spent retrying. (#823)
- Raise a neater RuntimeError when the correct async deps are not installed. (#826)
- Add support for synchronous TLS-in-TLS streams. (#840)
## 1.0.0 (October 6th, 2023)
From version 1.0 our async support is now optional, as the package has minimal dependencies by default.
For async support use either `pip install 'httpcore[asyncio]'` or `pip install 'httpcore[trio]'`.
The project versioning policy is now explicitly governed by SEMVER. See https://semver.org/.
- Async support becomes fully optional. (#809)
- Add support for Python 3.12. (#807)
## 0.18.0 (September 8th, 2023)
- Add support for HTTPS proxies. (#745, #786)
- Drop Python 3.7 support. (#727)
- Handle `sni_hostname` extension with SOCKS proxy. (#774)
- Change the type of `Extensions` from `Mapping[Str, Any]` to `MutableMapping[Str, Any]`. (#762)
## 0.17.3 (July 5th, 2023)
- Support async cancellations, ensuring that the connection pool is left in a clean state when cancellations occur. (#726)
- The networking backend interface has [been added to the public API](https://www.encode.io/httpcore/network-backends). Some classes which were previously private implementation detail are now part of the top-level public API. (#699)
- Graceful handling of HTTP/2 GoAway frames, with requests being transparently retried on a new connection. (#730)
- Add exceptions when a synchronous `trace callback` is passed to an asynchronous request or an asynchronous `trace callback` is passed to a synchronous request. (#717)
- Drop Python 3.7 support. (#727)
## 0.17.2 (May 23th, 2023)
- Add `socket_options` argument to `ConnectionPool` and `HTTProxy` classes. (#668)
- Improve logging with per-module logger names. (#690)
- Add `sni_hostname` request extension. (#696)
- Resolve race condition during import of `anyio` package. (#692)
- Enable TCP_NODELAY for all synchronous sockets. (#651)
## 0.17.1 (May 17th, 2023)
- If 'retries' is set, then allow retries if an SSL handshake error occurs. (#669)
- Improve correctness of tracebacks on network exceptions, by raising properly chained exceptions. (#678)
- Prevent connection-hanging behaviour when HTTP/2 connections are closed by a server-sent 'GoAway' frame. (#679)
- Fix edge-case exception when removing requests from the connection pool. (#680)
- Fix pool timeout edge-case. (#688)
## 0.17.0 (March 16th, 2023)
- Add DEBUG level logging. (#648)
- Respect HTTP/2 max concurrent streams when settings updates are sent by server. (#652)
- Increase the allowable HTTP header size to 100kB. (#647)
- Add `retries` option to SOCKS proxy classes. (#643)
## 0.16.3 (December 20th, 2022)
- Allow `ws` and `wss` schemes. Allows us to properly support websocket upgrade connections. (#625)
- Forwarding HTTP proxies use a connection-per-remote-host. Required by some proxy implementations. (#637)
- Don't raise `RuntimeError` when closing a connection pool with active connections. Removes some error cases when cancellations are used. (#631)
- Lazy import `anyio`, so that it's no longer a hard dependency, and isn't imported if unused. (#639)
- Raise `RuntimeError` if attempting to us UNIX domain sockets on Windows. (#619)
## 0.16.1 (November 17th, 2022)
- Fix HTTP/1.1 interim informational responses, such as "100 Continue". (#605)
## 0.16.0 (October 11th, 2022)
- Support HTTP/1.1 informational responses. (#581)
- Fix async cancellation behaviour. (#580)
- Support `h11` 0.14. (#579)
## 0.15.0 (May 17th, 2022)
- Drop Python 3.6 support (#535)
- Ensure HTTP proxy CONNECT requests include `timeout` configuration. (#506)
- Switch to explicit `typing.Optional` for type hints. (#513)
- For `trio` map OSError exceptions to `ConnectError`. (#543)
## 0.14.7 (February 4th, 2022)
- Requests which raise a PoolTimeout need to be removed from the pool queue. (#502)
- Fix AttributeError that happened when Socks5Connection were terminated. (#501)
## 0.14.6 (February 1st, 2022)
- Fix SOCKS support for `http://` URLs. (#492)
- Resolve race condition around exceptions during streaming a response. (#491)
## 0.14.5 (January 18th, 2022)
- SOCKS proxy support. (#478)
- Add proxy_auth argument to HTTPProxy. (#481)
- Improve error message on 'RemoteProtocolError' exception when server disconnects without sending a response. (#479)
## 0.14.4 (January 5th, 2022)
- Support HTTP/2 on HTTPS tunnelling proxies. (#468)
- Fix proxy headers missing on HTTP forwarding. (#456)
- Only instantiate SSL context if required. (#457)
- More robust HTTP/2 handling. (#253, #439, #440, #441)
## 0.14.3 (November 17th, 2021)
- Fix race condition when removing closed connections from the pool. (#437)
## 0.14.2 (November 16th, 2021)
- Failed connections no longer remain in the pool. (Pull #433)
## 0.14.1 (November 12th, 2021)
- `max_connections` becomes optional. (Pull #429)
- `certifi` is now included in the install dependencies. (Pull #428)
- `h2` is now strictly optional. (Pull #428)
## 0.14.0 (November 11th, 2021)
The 0.14 release is a complete reworking of `httpcore`, comprehensively addressing some underlying issues in the connection pooling, as well as substantially redesigning the API to be more user friendly.
Some of the lower-level API design also makes the components more easily testable in isolation, and the package now has 100% test coverage.
See [discussion #419](https://github.com/encode/httpcore/discussions/419) for a little more background.
There's some other neat bits in there too, such as the "trace" extension, which gives a hook into inspecting the internal events that occur during the request/response cycle. This extension is needed for the HTTPX cli, in order to...
* Log the point at which the connection is established, and the IP/port on which it is made.
* Determine if the outgoing request should log as HTTP/1.1 or HTTP/2, rather than having to assume it's HTTP/2 if the --http2 flag was passed. (Which may not actually be true.)
* Log SSL version info / certificate info.
Note that `curio` support is not currently available in 0.14.0. If you're using `httpcore` with `curio` please get in touch, so we can assess if we ought to prioritize it as a feature or not.
## 0.13.7 (September 13th, 2021)
- Fix broken error messaging when URL scheme is missing, or a non HTTP(S) scheme is used. (Pull #403)
## 0.13.6 (June 15th, 2021)
### Fixed
- Close sockets when read or write timeouts occur. (Pull #365)
## 0.13.5 (June 14th, 2021)
### Fixed
- Resolved niggles with AnyIO EOF behaviours. (Pull #358, #362)
## 0.13.4 (June 9th, 2021)
### Added
- Improved error messaging when URL scheme is missing, or a non HTTP(S) scheme is used. (Pull #354)
### Fixed
- Switched to `anyio` as the default backend implementation when running with `asyncio`. Resolves some awkward [TLS timeout issues](https://github.com/encode/httpx/discussions/1511).
## 0.13.3 (May 6th, 2021)
### Added
- Support HTTP/2 prior knowledge, using `httpcore.SyncConnectionPool(http1=False)`. (Pull #333)
### Fixed
- Handle cases where environment does not provide `select.poll` support. (Pull #331)
## 0.13.2 (April 29th, 2021)
### Added
- Improve error message for specific case of `RemoteProtocolError` where server disconnects without sending a response. (Pull #313)
## 0.13.1 (April 28th, 2021)
### Fixed
- More resilient testing for closed connections. (Pull #311)
- Don't raise exceptions on ungraceful connection closes. (Pull #310)
## 0.13.0 (April 21st, 2021)
The 0.13 release updates the core API in order to match the HTTPX Transport API,
introduced in HTTPX 0.18 onwards.
An example of making requests with the new interface is:
To instead including an optional dictionary of extensions on the request and response:
```python
def request(method, url, headers, stream, ext):
return (status_code, headers, stream, ext)
```
Having an open-ended extensions point will allow us to add later support for various optional features, that wouldn't otherwise be supported without these API changes.
In particular:
* Trailing headers support.
* HTTP/2 Server Push
* sendfile.
* Exposing raw connection on CONNECT, Upgrade, HTTP/2 bi-di streaming.
* Exposing debug information out of the API, including template name, template context.
- Add `PlainByteStream`, `IteratorByteStream`, `AsyncIteratorByteStream`. The `AsyncByteSteam` and `SyncByteStream` classes are now pure interface classes. (#133)
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