Announcing Tornado 6.6.0a1

[Ben Darnell]

The first alpha release of Tornado 6.6 is now available on pypi. Install it with `tornado==6.6.0a1`. This alpha release is not yet feature-complete; the final release of 6.6 is expected by mid-October. Major changes in this release include increased support for additional platforms: Users of free-threaded python builds, Windows on ARM, or linux on riscv, ppc, or s390x platforms are encouraged to test this release.

What's new in Tornado 6.6.0

===========================

Oct XX, 2026

------------

General changes

~~~~~~~~~~~~~~~

- Python 3.15 is now supported. Python 3.9 and 3.10 are no longer supported; 3.11 is the minimum

supported version.

- Free-threaded python interpreters are now supported; prebuilt wheels are available for 3.14t

and 3.15t.

- Windows on ARM is now supported and prebuilt wheels are available.

- Prebuilt wheels are now available for ``riscv64``, ``ppc64le``, and ``s390x`` architectures on

Linux. These architectures are experimental and have limited support and testing.

Deprecation notices

~~~~~~~~~~~~~~~~~~~

- The ``host`` argument to the `.HTTPServerRequest` constructor is deprecated (since

Tornado 6.5.2); use ``headers["Host"]`` instead. It will be removed in Tornado 6.7.

- The ``start_line`` argument to the ``HTTPServerRequest`` constructor will become required in

Tornado 6.7. The ``method``, ``uri``, and ``version`` arguments are deprecated and will be

removed at the same time. All remaining arguments will become keyword-only.

- `tornado.auth.OpenIdMixin` is deprecated and will be removed in Tornado 6.7 (this is a change

in the timeline; it was previously scheduled for removal in Tornado 7.0).

Type annotation changes

~~~~~~~~~~~~~~~~~~~~~~~

- `.tornado.gen.multi` now has overload annotations to indicate that its return type depends

on its inputs (list vs dict).

- `.HTTPServerRequest.method` and ``uri`` attributes are now typed as ``str`` instead of

``str | None``

``tornado.curl_httpclient``

~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The minimum supported version of libcurl is now 7.81 (which is the version shipped by

Ubuntu 22.04 LTS).

``tornado.simple_httpclient``

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``streaming_callback`` argument to ``SimpleAsyncHTTPClient.fetch`` may now be a coroutine.

``tornado.http1connection``

~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Invalid ``Host`` headers are now logged at the INFO level instead of as an uncaught exception.

`tornado.httputil`

~~~~~~~~~~~~~~~~~~

- If the ``start_line`` argument to `.HTTPServerRequest` is not provided, both ``method`` and

``uri`` must be provided.

`tornado.locks`

~~~~~~~~~~~~~~~

- A ``timeout`` value of zero will either return or raise immediately. Previously, zero was

treated as equivalent to ``None`` (wait forever). This affects `.Condition.wait`, `.Event.wait`,

`.Semaphore.acquire`, and `.Lock.acquire`.

`tornado.netutil`

~~~~~~~~~~~~~~~~~

- The default ``SSLContext`` objects are now lazily created on first use rather than at import time.

`tornado.platform.asyncio`

~~~~~~~~~~~~~~~~~~~~~~~~~~

- The selector thread used on Windows now cleans up its sockets correctly on interpreter exit,

preventing logged warnings.

`tornado.platform.caresresolver`

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``CaresResolver`` class (which has been deprecated since Tornado 6.2) requires pycares

version 4.x; it will not be updated to support pycares 5.x.

`tornado.queues`

~~~~~~~~~~~~~~~~

- A ``timeout`` value of zero will either return or raise immediately. Previously, zero was

treated as equivalent to ``None`` (wait forever). This affects `.Queue.get`, `.Queue.put`, and

`.Queue.join`.