Do i need to implement AGameMode for Client-Only game?

I am not going to use UE4 networking replication etc.
Server will be selfmade.

But, as far as i understand, AGameMode is made for Authoritative Host or for Single-Player game.

My client is not going to be nor Host, nor Single-player game. Its going to be Client-Only application.
Which class should i subclass for client game logic and interaction with server, if i am creating Client-Only game?
Should it be AGameState? or smth else?

As far as my tests showing, Client-Only build doesnt use GameMode, but it still constructed.

Gamemode is represent of game mode regardless of single or multi. Obviuesly in multiplayer this class will be on sever-side and be replicated to client. Role of this class does not change regardless what you do, so yes you will need to implement it and make it work with your server too, or else you use compliantly different game logic.

Ok, thx, i hope so. Anyway i decided not to use Client build config, i will use only Default config.