That depends. 9k is a valid, usable, map size. But issues like the specs of a player's computer, how dense the POI count is, how much terrain is having to be loaded and what their graphics setting are, etc, will determine if they can actually PLAY on the map.
If you are trying to play a 9k map on a hosted server? Check with their tech support. It may depend on the tier of your hosting plan. I know the Blue Fang Solutions tier for 14 players will NOT support a 9k map, I've tried it and they said "Nope, got to up the subscription tier for maps bigger than 8k."
What tool(s) are you using to make a 9k map? Teragon? Or something else?