[lcrmorin]

Propose Python 3.11 as the minimum supported version for the next release. Python 3.9 reached end of life on 2025-10-31 and Python 3.10 on 2026-10-01, per the Python support schedule.

This is a draft for maintainer agreement on the support floor and release timing. It is a compatibility-breaking change: Python 3.9/3.10 users must upgrade Python to install the next release; previous Feature-engine releases keep their original requirements. Support through Python 3.14 already exists (merged #892). No open overlapping Python-minimum upgrade PR was found.

Changes:

• Set Requires-Python to >=3.11 and remove the 3.9/3.10 classifiers.
• Replace the 3.9/3.10 CircleCI and tox jobs with an unpinned 3.11 job. Retain the pinned scikit-learn/pandas checks and Python 3.12–3.14 jobs.
• Move CircleCI quality/release tooling from Python 3.10 to the existing 3.11 image, and update release-job prerequisites.
• Align installation/contribution docs and add an unreleased compatibility note. Update the Python references in the legacy .github/workflow/workflow.yml without activating that dormant workflow.

Pandas, NumPy and scikit-learn requirements are unchanged. This proposal is separate from the sparse-input test-helper fix in #1108–#1110; dropping Python 3.9 is not needed to fix those failures.

Validation:

• Wheel and source distribution build successfully; wheel metadata rejects Python 3.9/3.10 and accepts 3.11–3.14.
• CircleCI YAML parses and all workflow jobs/release prerequisites resolve; tox lists the intended environments.
• Full suite: 2117 passed, 82 warnings in 86.66s (0:01:26). Tested on Python 3.11.16 with pandas 3.0.6, scikit-learn 1.9.1 and NumPy 2.4.6.
• Full remote CI matrix and CircleCI service-side validation remain pending.

Prepared with AI assistance. Maintainer review of the minimum version and release timing is requested.