Peer-Id
From version 0.80 onward, Transmission's peer-id is formatted Azureus style with one digit for the major version, two digits for the minor version, and one character to denote a stable release (0), nightly build (Z), or prerelease beta (X). For example:
-TR1330- — Official 1.33 release-TR133Z- — Nightly build between 1.33 and 1.34-TR133X- — Beta release of 1.34
Rationale: This differentiates between official and unofficial releases in a way easy for trackers to detect with simple string comparison. An official release (-TR1330-) is lexigraphically smaller than its post-release unsupported versions (-TR133Z- and -TR133X-), which in turn are lexigraphically smaller than the next official release (-TR1340-).
Before 0.80, versions of Transmission used two digits for the major version and two for the minor. For example, -TR0072- was Transmission 0.72.
User-Agent
Its User-Agent header follows a similar format, plus the VCS revision in parenthesis:
- Transmission/1.30X (6416) — Beta release leading up to version 1.30
- Transmission/1.32 (6455) — Official 1.32 release
- Transmission/1.32+ (6499) — Nightly build between 1.32 and 1.33