.. include:: _contributors.rst

.. currentmodule:: sklearn

.. _release_notes_1_9:

===========
Version 1.9
===========

..
  -- UNCOMMENT WHEN 1.9.0 IS RELEASED --
  For a short description of the main highlights of the release, please refer to
  :ref:`sphx_glr_auto_examples_release_highlights_plot_release_highlights_1_9_0.py`.


..
  DELETE WHEN 1.9.0 IS RELEASED
  Since October 2024, DO NOT add your changelog entry in this file.
..
  Instead, create a file named `<PR_NUMBER>.<TYPE>.rst` in the relevant sub-folder in
  `doc/whats_new/upcoming_changes/`. For full details, see:
  https://github.com/scikit-learn/scikit-learn/blob/main/doc/whats_new/upcoming_changes/README.md

.. include:: changelog_legend.inc

.. towncrier release notes start

.. _changes_1_9_dev0:

Version 1.9.dev0
================

**December 2025**

Changes impacting many modules
------------------------------

- |Enhancement| :class:`pipeline.Pipeline`, :class:`pipeline.FeatureUnion` and
  :class:`compose.ColumnTransformer` now raise a clearer
  error message when an estimator class is passed instead of an instance.
  By :user:`Anne Beyer <AnneBeyer>` :pr:`32888`

Support for Array API
---------------------

Additional estimators and functions have been updated to include support for all
`Array API <https://data-apis.org/array-api/latest/>`_ compliant inputs.

See :ref:`array_api` for more details.

- |Feature| :func:`sklearn.metrics.d2_absolute_error_score` and
  :func:`sklearn.metrics.d2_pinball_score` now support array API compatible inputs.
  By :user:`Virgil Chan <virchan>`. :pr:`31671`

:mod:`sklearn.metrics`
----------------------

- |Fix| :func:`metrics.d2_pinball_score` and :func:`metrics.d2_absolute_error_score` now
  always use the `"averaged_inverted_cdf"` quantile method, both with and
  without sample weights. Previously, the `"linear"` quantile method was used only
  for the unweighted case leading the surprising discrepancies when comparing the
  results with unit weights. Note that all quantile interpolation methods are
  asymptotically equivalent in the large sample limit, but this fix can cause score
  value changes on small evaluation sets (without weights).
  By :user:`Virgil Chan <virchan>`. :pr:`31671`

:mod:`sklearn.utils`
--------------------

- |Fix| The parameter table in the HTML representation of all scikit-learn
  estimators inheritiging from :class:`base.BaseEstimator`, displays
  each parameter documentation as a tooltip. The last tooltip of a
  parameter in the last table of any HTML representation was partially hidden.
  This issue has been fixed.
  By :user:`Dea María Léon <DeaMariaLeon>` :pr:`32887`

.. rubric:: Code and documentation contributors

Thanks to everyone who has contributed to the maintenance and improvement of
the project since version 1.8, including:

TODO: update at the time of the release.