diff --git a/temporal/api/worker/v1/worker_nexus_service_commands.proto b/temporal/api/worker/v1/worker_nexus_service_commands.proto
new file mode 100644
index 000000000..d4903d504
--- /dev/null
+++ b/temporal/api/worker/v1/worker_nexus_service_commands.proto
@@ -0,0 +1,49 @@
+syntax = "proto3";
+
+package temporal.api.worker.v1;
+
+option go_package = "go.temporal.io/api/worker/v1;worker";
+option java_package = "io.temporal.api.worker.v1";
+option java_multiple_files = true;
+option java_outer_classname = "WorkerNexusServiceCommandsProto";
+option ruby_package = "Temporalio::Api::Worker::V1";
+option csharp_namespace = "Temporalio.Api.Worker.V1";
+
+// (--
+/////////////////////////////////////////////////////////////////////
+// This file contains:
+// - Conventions between server and worker.
+// - Definitions for commands and payloads for server-worker communication via Nexus
+//
+// COMMUNICATION PROTOCOL:
+// - Transport: Nexus tasks on task queue
+// - Server identifier: "sys-worker-service"
+// - Task queue: /temporal-sys/worker-commands/{namespace}/{worker_grouping_key}
+//
+// WORKER COMMANDS CONVENTIONS:
+//
+// - Worker commands are used to manage worker configurations, operations, etc.
+// - Command names should match names defined in the server API.
+// - Command names are provided in StartOperationRequest.Operation field.
+//
+// PAYLOAD CONVENTIONS:
+//
+// - In/out payloads namings follow the same convention as the regular API:
+// - CommandNameRequest (input payload)
+// - CommandNameResponse (output payload).
+// - Empty payload if response is not needed/not expected
+//
+// --)
+
+// Request payload for the "cancel-activities" Nexus operation.
+message CancelActivitiesRequestPayload {
+    // Task tokens identifying the activities to cancel.
+    // Each token corresponds to a specific activity task that the worker received.
+    repeated bytes task_tokens = 1;
+}
+
+// Response payload for the "cancel-activities" Nexus operation.
+message CancelActivitiesResponsePayload {
+    // Empty for now. Can be extended to include cancellation status per activity.
+}
+