iTerm2 has a new drawing engine that uses Metal 2. For many users, this will significantly improve performance.
60 frame per second rendering. Buttery smooth!
Increased throughput (e.g., when you cat a giant file, it'll finish sooner.)
Most users will see improved latency (time between pressing a key and seeing it drawn.)
The Metal renderer is in the nightly builds and iTerm2 3.2beta1 and later.
The new renderer is not available for some configurations:
You must have macOS 10.12 or later.
Transparent windows are not supported. They must be opaque. This is because subpixel anti-aliasing becomes too complex.
You must disable ligatures for both ASCII and non-ASCII fonts in Prefs > Profiles > Text. Ligatures are very hard to support in a GPU-based renderer.
If you have adjusted Prefs > Advanced > Height of top and bottom margins in terminal panes to be less than 2, the Metal renderer will not be used.
Vertical spacing for your fonts (as configured in the font panel) must not be set to less than 100% (the default).
It is also temporarily disabled under certain conditions:
When another view, such as the find bar, is drawn overtop the terminal.
When your device is not plugged into a charger. This is controlled by Prefs > Advanced > Disable Metal renderer when not connected to power.
You can disable it in Prefs > General > GPU Rendering.
The easiest way to verify that it's working is to enable the FPS Meter (Prefs > Advanced > Show FPS meter). When the Metal renderer is in use it shows the current frame rate in magenta text in the top right of the session.