Read the license. This does not conform to the Open Source definition, nor the Free Software definition.

This is proprietary software.

This software and associated documentation files (the “Software”) may only be used in production, if you (and any entity that you represent) have agreed to, and are in compliance with, the Tabby Subscription Terms of Service, available at https://tabby.tabbyml.com/terms (the “Enterprise Terms”), or other agreement governing the use of the Software, as agreed by you and TabbyML, and otherwise have a valid Tabby Enterprise license for the correct number of user seats. Subject to the foregoing sentence, you are free to modify this Software and publish patches to the Software. You agree that TabbyML and/or its licensors (as applicable) retain all right, title and interest in and to all such modifications and/or patches, and all such modifications and/or patches may only be used, copied, modified, displayed, distributed, or otherwise exploited with a valid Tabby Enterprise license for the correct number of user seats. Notwithstanding the foregoing, you may copy and modify the Software for development and testing purposes, without requiring a subscription. You agree that Tabby and/or its licensors (as applicable) retain all right, title and interest in and to all such modifications. You are not granted any other rights beyond what is expressly stated herein. Subject to the foregoing, it is forbidden to copy, merge, publish, distribute, sublicense, and/or sell the Software.

https://github.com/TabbyML/tabby/blob/main/ee/LICENSE

https://opensource.org/osd/

https://www.gnu.org/philosophy/free-sw.html#fs-definition

The network effect in this article is seen as important for the adoption of free forges when projects choose them. But I don’t see anything about the importance of how many people use them for contributors to, well, contribute. I might have missed it though.

I would hope that programmers and people inclined to do so much as submit bug reports can sign up for an account.

User count doesn’t really matter for code hosting platforms. It’s not a social network.