On May 6, 2005, Metamod:Source 1.0 was released with SourceHook v4.1 as a backend. GameDLL wrapping was achieved by providing the engine with fake copies of the IServerGame* interfaces. Once the true GameDLL location was known it would be loaded by Metamod:Source. The fake interface then directly wrapped calls to the real GameDLL.
On October 21, 2005, the first major revision of Metamod:Source was released, featuring SourceHook v4.4, internal event listeners, dropped reliance on STL, and rewritten GameDLL hooking code. The Day of Defeat:Source release by Valve Software revealed that the binary interface between the engine and mod wasn't necessarily public or current, and MM:S's detection was improved for compatibility and speed. Furthermore, Metamod:Source stopped wrapping the GameDLL interfaces and began using SourceHook to hook them.
On January 7th, 2006, Metamod:Source was updated for SourceHook v4.3, but received no major API changes.
On August 16th, 2006, Metamod:Source was updated for SourceHook v4.4, minor API changes, bug fixes, and a sync to the latest HL2SDK.
On April 5th, 2007, Metamod:Source was updated with API for Valve Server Plugin interface hooking and crash-safe user message enumeration. An experimental gameinfo.txt update tool was also added. No SourceHook changes were made in this release.
Currently in development, Metamod:Source received a near complete overhaul to abstract engine-specific code to support Orange Box. Additionally, SourceHook received a massive overhaul and is now v5.0, adding global hooks and various major API simplifications. It is the first backwards compatibility break since 1.1.