diff --git a/ipn/backend.go b/ipn/backend.go
index 3e956f473..9ee3bc651 100644
--- a/ipn/backend.go
+++ b/ipn/backend.go
@@ -81,6 +81,13 @@ const (
 	NotifyInitialHealthState NotifyWatchOpt = 1 << 7 // if set, the first Notify message (sent immediately) will contain the current health.State of the client
 
 	NotifyRateLimit NotifyWatchOpt = 1 << 8 // if set, rate limit spammy netmap updates to every few seconds
+
+	// NotifyOmitLegacyNetmap, if set, causes the backend to not send Notify
+	// mesesages with the [Notify.NetMap] field populated. See that field's docs
+	// for background. Clients should use NodeUpdate, UserUpdate, etc.
+	// At some point in the future (maybe a year or two from 2025-01-04?), this will
+	// become the default and only way.
+	NotifyOmitLegacyNetmap NotifyWatchOpt = 1 << 9
 )
 
 // Notify is a communication from a backend (e.g. tailscaled) to a frontend
@@ -102,12 +109,23 @@ type Notify struct {
 	// For State InUseOtherUser, ErrMessage is not critical and just contains the details.
 	ErrMessage *string
 
-	LoginFinished *empty.Message     // non-nil when/if the login process succeeded
-	State         *State             // if non-nil, the new or current IPN state
-	Prefs         *PrefsView         // if non-nil && Valid, the new or current preferences
-	NetMap        *netmap.NetworkMap // if non-nil, the new or current netmap
-	Engine        *EngineStatus      // if non-nil, the new or current wireguard stats
-	BrowseToURL   *string            // if non-nil, UI should open a browser right now
+	LoginFinished *empty.Message // non-nil when/if the login process succeeded
+	State         *State         // if non-nil, the new or current IPN state
+	Prefs         *PrefsView     // if non-nil && Valid, the new or current preferences
+	Engine        *EngineStatus  // if non-nil, the new or current wireguard stats
+	BrowseToURL   *string        // if non-nil, UI should open a browser right now
+
+	// NetMap, if non-nil, the new or current network map.
+	//
+	// If [NotifyOmitLegacyNetmap] is used on an WatchIPNBus subscription, this
+	// field is always nil.
+	//
+	// Deprecated: while sent by default (as of 2025-01-04), it is a colossal
+	// type and on its way out. With large networks with many peers and high
+	// churn, sending this non-stop to GUI clients uses a lot of CPU and
+	// bandwidth. It was a quadratic mistake from day 1; see
+	// tailscale/tailscale#1909 and tailscale/tailscale#13390.
+	NetMap *netmap.NetworkMap // if non-nil, the new or current netmap
 
 	// FilesWaiting if non-nil means that files are buffered in
 	// the Tailscale daemon and ready for local transfer to the
@@ -153,9 +171,62 @@ type Notify struct {
 	// any changes to the user in the UI.
 	Health *health.State `json:",omitempty"`
 
+	// ResetNodesAndUsers, if true, means that all previously mentioned
+	// nodes and users should be forgotten.
+	//
+	// This is set to true when a new network map long poll to the control
+	// plane begins, but before any NodeUpdate or UserUpdate are sent.
+	ResetNodesAndUsers bool `json:",omitempty"`
+
+	// NodeUpdate is a map of node updates.
+	//
+	// The values are always non-nil.
+	NodeUpdate map[tailcfg.StableNodeID]*NodeUpdate `json:",omitempty"`
+
+	// UserUpdate is a map of user updates.
+	//
+	// The values are always non-nil.
+	UserUpdate map[tailcfg.UserID]*UserUpdate `json:",omitempty"`
+
 	// type is mirrored in xcode/IPN/Core/LocalAPI/Model/LocalAPIModel.swift
 }
 
+// NodeUpdate describes a change to a node in the network map.
+type NodeUpdate struct {
+	// NodeID is the integer form of the Node ID being updated or deleted.
+	NodeID tailcfg.NodeID
+
+	// Deleted is true if the node has been deleted from the network map.
+	Deleted bool `json:",omitempty"`
+
+	// IsSelf is true if this node is the current node.
+	// False or omitted means it's a peer.
+	IsSelf bool `json:",omitempty"`
+
+	// New is the new node information, if the node has been updated.
+	// It maybe omitted for delta updates, depending on the type of update
+	// and the client's WatchIPNBus subscription options.
+	New *tailcfg.Node `json:",omitempty"`
+
+	// Patch, if non-nil, describes the minimal version of the change made to the node.
+	// When Patch and New are both non-nil, the New field represents the state
+	// after the Patch has been applied.
+	Patch *tailcfg.PeerChange `json:",omitempty"`
+}
+
+// UserUpdate describes a change to a user in the network map.
+type UserUpdate struct {
+	UserID tailcfg.UserID
+
+	// Deleted is true if the user has been deleted from the network map.
+	// That is, the user is no longer referenced by any node in the network map.
+	Deleted bool `json:",omitempty"`
+
+	// Profile is the new user profile, if the user has been newly added or
+	// updated. If Delete is true, this is omitted.
+	Profile *tailcfg.UserProfile `json:",omitempty"`
+}
+
 func (n Notify) String() string {
 	var sb strings.Builder
 	sb.WriteString("Notify{")
diff --git a/ipn/ipnlocal/bus.go b/ipn/ipnlocal/bus.go
index 111a877d8..0b435b7be 100644
--- a/ipn/ipnlocal/bus.go
+++ b/ipn/ipnlocal/bus.go
@@ -154,6 +154,9 @@ func isNotableNotify(n *ipn.Notify) bool {
 		n.LoginFinished != nil ||
 		!n.DriveShares.IsNil() ||
 		n.Health != nil ||
+		n.ResetNodesAndUsers ||
+		n.NodeUpdate != nil ||
+		n.UserUpdate != nil ||
 		len(n.IncomingFiles) > 0 ||
 		len(n.OutgoingFiles) > 0 ||
 		n.FilesWaiting != nil
diff --git a/ipn/ipnlocal/bus_test.go b/ipn/ipnlocal/bus_test.go
index 5c75ac54d..74610200d 100644
--- a/ipn/ipnlocal/bus_test.go
+++ b/ipn/ipnlocal/bus_test.go
@@ -12,6 +12,7 @@ import (
 
 	"tailscale.com/drive"
 	"tailscale.com/ipn"
+	"tailscale.com/tailcfg"
 	"tailscale.com/tstest"
 	"tailscale.com/tstime"
 	"tailscale.com/types/logger"
@@ -45,6 +46,10 @@ func TestIsNotableNotify(t *testing.T) {
 			continue
 		case "DriveShares":
 			n.DriveShares = views.SliceOfViews[*drive.Share, drive.ShareView](make([]*drive.Share, 1))
+		case "NodeUpdate":
+			n.NodeUpdate = map[tailcfg.StableNodeID]*ipn.NodeUpdate{}
+		case "UserUpdate":
+			n.UserUpdate = map[tailcfg.UserID]*ipn.UserUpdate{}
 		default:
 			rf := reflect.ValueOf(n).Elem().Field(i)
 			switch rf.Kind() {
@@ -54,6 +59,8 @@ func TestIsNotableNotify(t *testing.T) {
 				rf.SetString("foo")
 			case reflect.Slice:
 				rf.Set(reflect.MakeSlice(rf.Type(), 1, 1))
+			case reflect.Bool:
+				rf.SetBool(true)
 			default:
 				t.Errorf("unhandled field kind %v for %q", rf.Kind(), sf.Name)
 			}