Black 25.12.0

Please test out the draft 2026 style in version 26.1a1! This style will be finalized in the January release (26.1.0). Most of the changes in --preview will be in the 2026 stable style, but not all. Please share your feedback!

This release (25.12.0) will still produce the 2025 style.

Highlights

• Black no longer supports running with Python 3.9 (#4842)

Stable style

• Fix bug where comments preceding # fmt: off/# fmt: on blocks were incorrectly removed, particularly affecting Jupytext's # %% [markdown] comments (#4845)
• Fix crash when multiple # fmt: skip comments are used in a multi-part if-clause, on string literals, or on dictionary entries with long lines (#4872)
• Fix possible crash when fmt: directives aren't on the top level (#4856)

Preview style

• Fix fmt: skip skipping the line after instead of the line it's on (#4855)
• Remove unnecessary parentheses from the left-hand side of assignments while preserving magic trailing commas and intentional multiline formatting (#4865)
• Fix fix_fmt_skip_in_one_liners crashing on with statements (#4853)
• Fix fix_fmt_skip_in_one_liners crashing on annotated parameters (#4854)
• Fix new lines being added after imports with # fmt: skip on them (#4894)

Packaging

• Releases now include arm64 Windows binaries and wheels (#4814)

Integrations

• Add output-file input to GitHub Action psf/black to write formatter output to a file for artifact capture and log cleanliness (#4824)