diff --git a/pkg/vmcp/server/peer_probe.go b/pkg/vmcp/server/peer_probe.go
index 9947760f8b..08c9d827ce 100644
--- a/pkg/vmcp/server/peer_probe.go
+++ b/pkg/vmcp/server/peer_probe.go
@@ -27,8 +27,14 @@ type peerProbeKey struct{}
 // peerProbeMethods are the MCP methods a peer probe may send: the handshake and
 // the capability lists that the health checker's ListCapabilities runs. A probe
 // never calls a tool, reads a resource or gets a prompt.
+//
+// server/discover is the Modern (2026-07-28) handshake. Once the peer has
+// cached a backend as Modern, its health checker opens with it instead of
+// initialize. Refusing it makes the peer read a 403 as an auth failure, mark
+// the backend unauthenticated and open its circuit breaker.
 var peerProbeMethods = map[string]bool{
 	"initialize":                true,
+	"server/discover":           true,
 	"notifications/initialized": true,
 	"ping":                      true,
 	"tools/list":                true,
diff --git a/pkg/vmcp/server/serve_health_probe_test.go b/pkg/vmcp/server/serve_health_probe_test.go
index 3b39a80e90..0451afea8c 100644
--- a/pkg/vmcp/server/serve_health_probe_test.go
+++ b/pkg/vmcp/server/serve_health_probe_test.go
@@ -30,6 +30,14 @@ func TestPeerProbeMiddleware(t *testing.T) {
 		listBody = `{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}`
 		callBody = `{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"echo"}}`
 		getBody  = `{"jsonrpc":"2.0","id":4,"method":"prompts/get","params":{"name":"p"}}`
+		// The Modern (2026-07-28) health probe opens with server/discover
+		// instead of initialize (pkg/vmcp/client probeRevision and
+		// modernListCapabilities).
+		discoverBody = `{"jsonrpc":"2.0","id":5,"method":"server/discover","params":{"_meta":{` +
+			`"io.modelcontextprotocol/protocolVersion":"2026-07-28",` +
+			`"io.modelcontextprotocol/clientCapabilities":{},` +
+			`"io.modelcontextprotocol/clientInfo":{"name":"toolhive-vmcp","version":"test"}}}}`
+		listenBody = `{"jsonrpc":"2.0","id":6,"method":"subscriptions/listen","params":{}}`
 	)
 	tests := []struct {
 		name       string
@@ -41,6 +49,8 @@ func TestPeerProbeMiddleware(t *testing.T) {
 	}{
 		{"probe initialize is marked", http.MethodPost, health.ProbeHeaderValue, initBody, true, true},
 		{"probe tools/list is marked", http.MethodPost, health.ProbeHeaderValue, listBody, true, true},
+		{"probe server/discover is marked", http.MethodPost, health.ProbeHeaderValue, discoverBody, true, true},
+		{"probe subscriptions/listen is refused", http.MethodPost, health.ProbeHeaderValue, listenBody, false, false},
 		{"probe tools/call is refused", http.MethodPost, health.ProbeHeaderValue, callBody, false, false},
 		{"probe prompts/get is refused", http.MethodPost, health.ProbeHeaderValue, getBody, false, false},
 		{"probe with an unparsable body is refused", http.MethodPost, health.ProbeHeaderValue, `not json`, false, false},