# ruff 0.16.4

- Product: ruff (https://whatsnew.fyi/product/ruff)
- Vendor: ruff
- Date: 2026-08-20
- Version: 0.16.4
- Original notes: https://github.com/astral-sh/ruff/releases/tag/0.16.4
- Permalink: https://whatsnew.fyi/product/ruff/releases/0.16.4

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

---

- **added** — Add autofix for PTH116 in flake8-use-pathlib
- **changed** — Restrict delete-full-slice to lists (FURB131) in refurb
- **changed** — Skip FURB101 and FURB103 when the open argument is a file descriptor in refurb
- **fixed** — Fix InvalidInstruction on Windows CPUs that do not support POPCNT
- **fixed** — Emit semantic syntax errors in string type definitions as F722 in pyflakes
- **fixed** — Allow os._exit imports in import-private-name (PLC2701) in pylint
- **changed** — Align mixed t-string/bytes error message with CPython 3.14 in syntax-errors
- **changed** — Add ctypes.LittleEndianStructure and related types to existing exception (RUF012) in ruff
- **added** — Detect duplicate keyword arguments in syntax-errors
- **added** — Detect parameters declared nonlocal in syntax-errors
- **changed** — Offer display-only fixes and mark safe fixes preferred in server
- **added** — Support pull diagnostics for notebook cells in server
- **fixed** — Fix s390x stacker assembly in release builds
- **fixed** — Guarantee minimum stack size when parsing a module, standalone expression, and suites
- **changed** — Reduce configuration deserialization code size
- **fixed** — Check packed AST index bounds

##### Release Notes

Released on 2026-08-20.

###### Preview features

- \[`flake8-use-pathlib`\] Add autofix for `PTH116` ([#26460](https://github.com/astral-sh/ruff/pull/26460))
- \[`refurb`\] Restrict `delete-full-slice` to lists (`FURB131`) ([#27711](https://github.com/astral-sh/ruff/pull/27711))
- \[`refurb`\] Skip `FURB101` and `FURB103` when the `open` argument is a file descriptor ([#27643](https://github.com/astral-sh/ruff/pull/27643))

###### Bug fixes

- Fix `InvalidInstruction` on Windows CPUs that do not support `POPCNT` ([#27803](https://github.com/astral-sh/ruff/pull/27803))
- \[`pyflakes`\] Emit semantic syntax errors in string type definitions as `F722` ([#27835](https://github.com/astral-sh/ruff/pull/27835))
- \[`pylint`\] Allow `os._exit` imports in `import-private-name` (`PLC2701`) ([#27738](https://github.com/astral-sh/ruff/pull/27738))

###### Rule changes

- [syntax-errors] Align mixed t-string/bytes error message with CPython 3.14 ([#27766](https://github.com/astral-sh/ruff/pull/27766))
- \[`ruff`\] Add `ctypes.LittleEndianStructure` and related types to existing exception (`RUF012`) ([#27753](https://github.com/astral-sh/ruff/pull/27753))
- [syntax-errors] Detect duplicate keyword arguments ([#17804](https://github.com/astral-sh/ruff/pull/17804))
- [syntax-errors] Detect parameters declared `nonlocal` ([#27628](https://github.com/astral-sh/ruff/pull/27628))

###### Server

- Offer display-only fixes and mark safe fixes preferred ([#27807](https://github.com/astral-sh/ruff/pull/27807))
- Support pull diagnostics for notebook cells ([#27779](https://github.com/astral-sh/ruff/pull/27779))

###### Documentation

- Add default indicator to rules table ([#27724](https://github.com/astral-sh/ruff/pull/27724))
- Fix broken link to Python docs ([#27757](https://github.com/astral-sh/ruff/pull/27757))

###### Other changes

- Fix s390x stacker assembly in release builds ([#27776](https://github.com/astral-sh/ruff/pull/27776))
- Guarantee minimum stack size when parsing a module, standalone expression, and suites ([#25464](https://github.com/astral-sh/ruff/pull/25464))
- Reduce configuration deserialization code size ([#27924](https://github.com/astral-sh/ruff/pull/27924))
- Check packed AST index bounds ([#27849](https://github.com/astral-sh/ruff/pull/27849))

###### Contributors

- [@AbhinavMir](https://github.com/AbhinavMir)
- [@eduardorittner](https://github.com/eduardorittner)
- [@royb3](https://github.com/royb3)
- [@MichaReiser](https://github.com/MichaReiser)
- [@carljm](https://github.com/carljm)
- [@rosstitmarsh](https://github.com/rosstitmarsh)
- [@ntBre](https://github.com/ntBre)
- [@zaniebot](https://github.com/zaniebot)
- [@ewdurbin](https://github.com/ewdurbin)
- [@woodruffw](https://github.com/woodruffw)
- [@Sacrimento](https://github.com/Sacrimento)
- [@lakshayxi](https://github.com/lakshayxi)
- [@WhiteFox0-0](https://github.com/WhiteFox0-0)
- [@baltasarblanco](https://github.com/baltasarblanco)

##### Install ruff 0.16.4

###### Install prebuilt binaries via shell script

```sh
curl --proto '=https' --tlsv1.2 -LsSf https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-installer.sh | sh
```

###### Install prebuilt binaries via powershell script

```sh
powershell -ExecutionPolicy Bypass -c "irm https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-installer.ps1 | iex"
```

##### Download ruff 0.16.4

|  File  | Platform | Checksum |
|--------|----------|----------|
| [ruff-aarch64-apple-darwin.tar.gz](https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-aarch64-apple-darwin.tar.gz) | Apple Silicon macOS | [checksum](https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-aarch64-apple-darwin.tar.gz.sha256) |
| [ruff-x86_64-apple-darwin.tar.gz](https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-x86_64-apple-darwin.tar.gz) | Intel macOS | [checksum](https://releases.astral.sh/github/ruff/releases/download/0.16.4/ruff-x86_64-

_[Truncated at 4000 characters — full notes: https://github.com/astral-sh/ruff/releases/tag/0.16.4]_