Transmission has been built from the ground up to be a powerful, yet lightweight BitTorrent client. Its simple, intuitive interface is designed to integrate tightly with whatever computing environment you choose to use.

Transmission strikes a balance between providing useful functionality without feature bloat. Furthermore, it is free for anyone to use or modify.

Features

• Uses fewer resources than other clients
• Native Mac, GTK+ and Qt GUI clients
• Daemon ideal for servers, embedded systems, and headless use
• All these can be remote controlled by Web and Terminal clients
• Local Peer Discovery
• Full encryption, DHT, µTP, PEX and Magnet Link support

Transmission runs natively on over five operating systems. Seamless configuration of your network, intelligent banning of peers who send corrupted data, and built in Peer Exchange are some of the features which enable Transmission to download your files as quickly as possible. All this is done in the background, without the user having to worry about complicated settings.

These days, bandwidth is a precious commodity. Transmission allows you to ration this commodity efficiently. You might want to queue your torrents for maximum performance. Or throttle their speed during peak periods.

Transmission easily lets you do both, and thus only works its hardest when you want it to. Support for Growl notifications and dock badging keep you updated with what’s going on so you can get back to doing more important things.

NOTE: Transmission is fully open source, with most code licensed under the liberal MIT License and with select code licensed under the GNU General Public License.

What’s New

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 libdeflate, a “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 (e.g. 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!

What’s New Since 4.0.0-beta.3

libtransmission (All Platforms)

• Added a new setting, torrent-added-verify-mode, to force-verify added torrents. (#4611)
• Improved handling of webseed servers that do not support Range requests or 206 Partial Content. (#4601)
• Improved handling of webseed servers that return a content-encoding that was not requested. (#4609)
• Fixed 4.0.0-beta.3 potential socket leak. (#4616)
• Fixed 4.0.0-beta.3 regression that failed to detect largefile build flags on 32bit systems. (#4627)
• Fixed 4.0.0-beta.1 UI bug when removing a tracker from the announce list. (#4635)
• Improved error handling when receiving corrupt piece data from peers. (#4665)
• Fixed 4.0.0-beta.1 FTBFS error on CentOS 7. (#4673, #4675)
• Made small performance improvements in libtransmission. (#4577, #4679)
• Dropped libiconv dependency in libtransmission. (#4565)
• Updated 403 RPC error message. (#4567)
• Bumped libdeflate snapshot to 1.17. (#4596)

macOS Client

• Fixed two Help menus in macOS. (#4500)
• Fixed bug that caused magnet links to always be paused when added. (#4528)
• Fixed 4.0.0-beta.1 regression that broke the Piece View “blinking” when a piece completes. (#4587)
• Ensured that the preferences window is centered the first time it is shown. (#4659)
• Fixed 4.0.0-beta.1 regression that incorrectly handled corrupt blocklists. (#4705)
• Increased the font size in the main window’s torrent list. (#4557)
• Fixed libpsl dependency build issue on macOS. (#4642)

Qt Client

• Made display order of speed limits consistent between Properties, Details dialogs. (#4677)

GTK Client

• Fixed 4.0.0-beta.1 regression making it impossible to close “Set location” dialog (GTK 3 only). (#4625)
• Fixed 4.0.0-beta.2 regression leading to crash during progress bars rendering on some systems. (#4688)

Web Client

• Fixed 4.0.0-beta.1 potential crash when detecting mime-types. (#4569)
• Fixed 4.0.0-beta.1 regression that broke file priority buttons in the web client. (#4610)

Daemon

• Fixed stderr logging issue when running as a systemd unit. (#4612)

transmission-remote

• Fixed 4.0.0-beta.1 regression when displaying session info. (#4624)
• Fixed 4.0.0-beta.1 regression when displaying tracker info. (#4633)