The macOS Screen Sharing app has a “High Performance” mode (macOS 15+, Apple silicon only) that feels native when used in-combination with a low-latency link. One of the major downsides is that the application refuses to run a more than 1 high performance session. The limit is understandable for the server component, but why is the client limited? Surely the device is capable of more than 1 video decoding stream.

If you try to open a second session and you get:

To continue, close the active session.

I could not find anyone online documenting a way around the client limit, so here is one such way. The limit is enforced per-process, and not system-wide. So to launch additional high performance sessions, you can simply launch a second instance of the client and then connect to your second remote mac.

open -n -a "Screen Sharing"

Research

The feature’s internal name is “ProMode”. Static analysis of the client (/System/Applications/Utilities/Screen Sharing.app, ScreenSharing.framework, ScreenSharingUI.framework, and ScreenSharingKit.framework) locates the entire gate in the app binary, in a singleton class called SessionControllerManager.

The check is a plain nil-test:

// -[SessionControllerManager hasOpenProModeSession]
return activeProModeSession != nil;

Binary Ninja: -[SessionControllerManager hasOpenProModeSession] returns activeProModeSession != nil

And activeProModeSession simply walks this process’s own window controllers, held in the instance variable _sessionControllers, and returns the first whose view is running the High Performance media stream (isUsingAVCMediaStream):

// -[SessionControllerManager activeProModeSession]
for (group in self->_sessionControllers)
    for (windowController in group)
        if (windowController.sessionView.isUsingAVCMediaStream)
            return windowController;
return nil;

Binary Ninja Pseudo Objective-C: -[SessionControllerManager activeProModeSession] retaining [self sessionControllers] and fast-enumerating this process's window controllers

Binary Ninja Pseudo Objective-C: the inner loop returning the controller when [obj isUsingAVCMediaStream] is true, else nullptr

There is no cross-process state. The gate reads only self->_sessionControllers, an in-memory ivar populated by this instance’s own addSession / addSessionWithURL:…. Since the state is contained to within the process, a second process gets a fresh SessionControllerManager with an empty _sessionControllers, so activeProModeSession is nil, hasOpenProModeSession is false, and the second session connects.

Symbol References

SessionControllerManager, activeProModeSession, hasOpenProModeSession, closeOpenProModeSession, openProModeSessionDisplayName, _sessionControllers, +sharedManager
SSSession, appWantsProModeInterface, setAppWantsProModeInterface:, doesServerSupportProMode, maxVirtualDisplays
SSSessionView, hasOpenProModeSession, isUsingAVCMediaStream, ssSessionWantsProModeInterface:
ScreenSharingUI.DisplayConfigurationViewModel, hasOpenProModeSession, maxVirtualDisplays, PromodeDisplayOptionsPickerView
Strings: "Cannot add more than one active High Performance session.", "ProMode enabled", "ProModeActive", "High Performance", "To continue, close the active session."

Multiple sessions for macOS High Performance Screen Sharing

Research

Symbol References