Download Transmission 4.0.0

The final release of Transmission version 4.0 has been released. This torrent client uses few resources, is cross-platform and open source, and has a simple and clear interface. The program was developed for use on macOS, but on the download page versions for Windows, Linux, FreeBSD and some NAS systems can also be found. In version 4.0.0, the program has been rewritten in C++, making it perform better and use fewer resources. The changelog for this release can be found below:

Highlights

This is a major release, both in numbering and in effort! It’s been in active development for over a year and has a huge list of changes — over a thousand commits — since Transmission 3.00. Some of the highlights include:

• Resource Efficiency – Use less memory and fewer CPU cycles
• Better Community – Pull requests welcomed and used
• Code Modernization – Migrated from C90 to modern C++
• New Features – What would a major release be without them?

Resource Efficiency

• The code has been extensively profiled and improved to fix inefficient code and memory use. For example, a stress test of starting transmission-daemon with 25,000 torrents is almost entirely IO-bound, using 50% fewer CPU cycles and 70% fewer memory allocations than Transmission 3.00.
• The remote control GUIs (transmission-qt and transmission-web) now use the RPC API “table” mode, resulting in smaller payloads / less bandwidth use.
• RPC payloads are now compressed using libdeflatea “heavily optimized [library that is] significantly faster than the zlib library.”

Community

• The project is much more responsive to bug reports and code submissions than it has been in the past.
• There is a new group of volunteer contributors who are working on Transmission!
• Transmission 4.0.0 includes over 350 new community commits (see the Thank You section below and in the previous 4.0.0 betas) since 3.00 and welcomes new contributors.
• Documentation has been moved into the transmission/transmission so that contributors can submit PRs to improve it.

Code Modernization

• The entire codebase has been migrated from C to C++. In the process, we’ve removed thousands of lines of custom code and used standard C++ tools instead. The core’s code has shrunk by 18%. The core codebase has been extensively refactored to be more testable and maintainable.
• The GTK client has been ported to gtkmm.
• The Web client has been rewritten in modern JavaScript and no longer uses jQuery. The entire gzipped bundle is now 68K.
• The unit tests have been expanded and ported to Google Test. Clang sanitizer builds are run during CI.
• The core library is now fuzz tested.
• Transmission now uses Sonarcloud, Coverity, LGTM, and clang-tidy static analysis on new code. Several hundred code warnings have been fixed compared to Transmission 3.00.

New Features

• Support for using BitTorrent v2 torrents and hybrid torrents. (Support for creating v2 and hybrid torrents is slated for an upcoming release.)
• Users can now set “default” trackers that can be used to announce all public torrents.
• Newly-added seeds can start immediately and verify pieces on demand, instead of needing a full verify before seeding can begin. (#2626)
• Added an option to omit potentially-identifying information (eg User-Agent and date created) when creating new torrents. (#3452)
• The Web client has been rewritten and now supports mobile use.
• When creating new torrents, users can now specify the piece size. (#3768, #3145, #2805)
• IPv6 blocklists are now supported. (#3835)
• Beginning with 4.0.0-beta.1, Transmission releases now use semver versioning.
• Dozens of other new features — too many to list here! We’ve been working on this for a year!