* ``arm64-apple-ios`` and ``arm64-apple-ios-simulator`` are both

now :pep:`11` tier 3 platforms.

(:ref:`PEP 730 <whatsnew313-platform-support>` written

and implementation contributed by Russell Keith-Magee in :gh:`114099`.)

* ``wasm32-wasi`` is now a :pep:`11` tier 2 platform.

(Contributed by Brett Cannon in :gh:`115192`.)

* ``wasm32-emscripten`` is no longer a :pep:`11` supported platform.

(Contributed by Brett Cannon in :gh:`115192`.)

* Building CPython now requires a compiler with support for the C11 atomic

library, GCC built-in atomic functions, or MSVC interlocked intrinsics.

* SQLite 3.15.2 or newer is required to build

the :mod:`sqlite3` extension module.

* CPython now bundles the `mimalloc library`_ by default.

It is licensed under the MIT license;

see :ref:`mimalloc license <mimalloc-license>`.

The bundled mimalloc has custom changes, see :gh:`113141` for details.

(Contributed by Dino Viehland in :gh:`109914`.)

.. _mimalloc library: https://github.com/microsoft/mimalloc/

* The :file:`configure` option :option:`--with-system-libmpdec`

now defaults to ``yes``.

The bundled copy of ``libmpdecimal`` will be removed in Python 3.15.

* Python built with :file:`configure` :option:`--with-trace-refs`

(tracing references) is now ABI compatible with the Python release build

and :ref:`debug build <debug-build>`.

* On POSIX systems, the pkg-config (``.pc``) filenames now include the ABI

flags. For example, the free-threaded build generates ``python-3.13t.pc``

and the debug build generates ``python-3.13d.pc``.