Selenium 4.39 Released!

Today we’re happy to announce that Selenium 4.39 has been released!

By Diego Molina @diemol | Saturday, December 06, 2025

Selenium 4.39 Released

Selenium 4.39 is a feature-rich release with numerous improvements across the board. It brings enhancements to BiDi across Java, Python, and .NET, more emulation commands, major updates to Dynamic Grid behavior, and continuous work on JSpecify annotations. It also includes docstring cleanups, test infra upgrades, and build system optimizations.

Highlights

Chrome DevTools support is now: v143, v142, and v141.
BiDi Enhancements Across Languages: New emulation and download behavior commands for Java, Python, and .NET.
Dynamic Grid Improvements: Better container handling, new labels, and minimum Docker API version enforcement.
Docstring and Type Hinting: Continued work on Python docstrings using Google style and improving type hints.
JSpecify Coverage in Java: Many new annotations for type-safety and better tooling support.
Build & CI Enhancements: Optimized workflows, Bazel module updates, and CI improvements across languages.

Language-specific Changes

Java

BiDi:
- Support for:
  - emulation.setTimezoneOverride
  - emulation.setScriptingEnabled
  - emulation.setUserAgentOverride
  - browser.setDownloadBehavior
  - browsingContext.setViewport(null, null)
- Refactored request interception tests with CORS handling.
JSpecify annotations:
- CommandCodec, CommandInfo, CommandPayload, Color, ChromiumDriver, and more.
Other:
- Prevent logging debug logs at INFO level.
- Fixes for PrintOptions.setPageRanges, ClassCastException, and Chrome tests on Windows.
- Improvements to exception handling and collection simplification.

Python

BiDi:
- Added:
  - set_locale_override
  - set_scripting_enabled
  - set_screen_orientation_override
  - set_download_behavior
  - set_user_agent_override
  - Viewport reset command
- Enabled download event tests for Firefox.
Documentation & Type Hints:
- Full docstring conversion to Google format.
- Removed noqa markers, improved type annotations with union syntax.
Dev/Tooling:
- Bumped pytest, ruff, mypy, and urllib3.
- WebSocket improvements (daemon threads).
- Test reuse and performance improvements.

.NET

BiDi:
- Improved event subscription and emulation module support.
- Better JSON (de)serialization contexts per module.
- Viewport reset, record equality, hydration, and type unification improvements.
- Added Permissions module.
General:
- Migrated solution to .slnx.
- Removed obsolete dependencies (Newtonsoft.Json, FtpProxy).
- Syntax highlighting improvements for JS strings.
- Updated build tools (paket, rules_dotnet).

Ruby

Fixed flaky devtools_spec.rb.
Minor BiDi updates.

Rust (Selenium Manager)

Bazel migration of rules_rust.

Grid

Minimum Docker API 1.44 support.
Improved:
- Session ID handling
- Container labels
- Compose stack grouping
- Docker client logic
Tracking SessionRemovalInfo and improved session map cleanup.