diff --git a/docs/book/src/reference/labels_and_annotations.md b/docs/book/src/reference/labels_and_annotations.md
index 271c645650ea..1c66bec7ace3 100644
--- a/docs/book/src/reference/labels_and_annotations.md
+++ b/docs/book/src/reference/labels_and_annotations.md
@@ -42,6 +42,7 @@
 | topology.cluster.x-k8s.io/defer-upgrade                          | It can be used to defer the Kubernetes upgrade of a single MachineDeployment topology. If the annotation is set on a MachineDeployment topology in Cluster.spec.topology.workers, the Kubernetes upgrade for this MachineDeployment topology is deferred. It doesn't affect other MachineDeployment topologies.                                                                                                                                                                                                                                             |
 | topology.cluster.x-k8s.io/dry-run                                | It is an annotation that gets set on objects by the topology controller only during a server side dry run apply operation. It is used for validating update webhooks for objects which get updated by template rotation (e.g. InfrastructureMachineTemplate). When the annotation is set and the admission request is a dry run, the webhook should deny validation due to immutability. By that the request will succeed (without any changes to the actual object because it is a dry run) and the topology controller will receive the resulting object. |
 | topology.cluster.x-k8s.io/hold-upgrade-sequence                  | It can be used to hold the entire MachineDeployment upgrade sequence. If the annotation is set on a MachineDeployment topology in Cluster.spec.topology.workers, the Kubernetes upgrade for this MachineDeployment topology and all subsequent ones is deferred.                                                                                                                                                                                                                                                                                            |
+| topology.cluster.x-k8s.io/upgrade-concurrency                    | It can be used to configure the maximum concurrency while upgrading MachineDeployments of a classy Cluster. It is set as a top level annotation on the Cluster object. The value should be >= 1. If unspecified the upgrade concurrency will default to 1.                                                                                                                                                                                                                                                                                                  |
 | machine.cluster.x-k8s.io/certificates-expiry                     | It captures the expiry date of the machine certificates in RFC3339 format. It is used to trigger rollout of control plane machines before certificates expire. It can be set on BootstrapConfig and Machine objects. The value set on Machine object takes precedence. The annotation is only used by control plane machines.                                                                                                                                                                                                                               |
 | machine.cluster.x-k8s.io/exclude-node-draining                   | It explicitly skips node draining if set.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
 | machine.cluster.x-k8s.io/exclude-wait-for-node-volume-detach     | It explicitly skips the waiting for node volume detaching if set.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |