Gemini will be releasing a new version of the Observing Tool (2021B.1.1.2) on Thursday, October 14, which includes several improvements, most notably support for the updated Horizons non-sidereal target database API.
The Gemini Observing Databases will be offline briefly on Thursday as each site is updated, during which time OT synchronizations and file transfers will be unavailable.
This version of the OT is highly recommended, especially for users with non-sidereal targets, but it is not required.
The new OT will be available for download on Thursday after the update, and the installation instructions are linked on the Observing Tool web page.
See the the Release Notes for a complete list of changes.