diff --git a/proto/opamp.proto b/proto/opamp.proto
index a1e77e1..6be7b10 100644
--- a/proto/opamp.proto
+++ b/proto/opamp.proto
@@ -25,8 +25,8 @@ option go_package = "github.com/open-telemetry/opamp-go/protobufs";
 message AgentToServer {
     // Globally unique identifier of the running instance of the Agent. SHOULD remain
     // unchanged for the lifetime of the Agent process.
-    // Recommended format: https://github.com/ulid/spec
-    string instance_uid = 1;
+    // MUST be 16 bytes long and SHOULD be generated using UUID v7 spec.
+    bytes instance_uid = 1;
 
     // The sequence number is incremented by 1 for every AgentToServer sent
     // by the Agent. This allows the Server to detect that it missed a message when
@@ -148,7 +148,7 @@ message CertificateRequest {
 message ServerToAgent {
     // Agent instance uid. MUST match the instance_uid field in AgentToServer message.
     // Used for multiplexing messages from/to multiple agents using one message stream.
-    string instance_uid = 1;
+    bytes instance_uid = 1;
 
     // error_response is set if the Server wants to indicate that something went wrong
     // during processing of an AgentToServer message. If error_response is set then
@@ -804,7 +804,8 @@ enum PackageStatusEnum {
 message AgentIdentification {
     // When new_instance_uid is set, Agent MUST update instance_uid
     // to the value provided and use it for all further communication.
-    string new_instance_uid = 1;
+    // MUST be 16 bytes long and SHOULD be generated using UUID v7 spec.
+    bytes new_instance_uid = 1;
 }
 
 /////////////////////////////////////////////////////////////////////////////////////
diff --git a/specification.md b/specification.md
index 63aab57..4f4fd6d 100644
--- a/specification.md
+++ b/specification.md
@@ -479,7 +479,7 @@ document are specified in
 
 ```protobuf
 message AgentToServer {
-    string instance_uid = 1;
+    bytes instance_uid = 1;
     uint64 sequence_num = 2;
     AgentDescription agent_description = 3;
     uint64 capabilities = 4;
@@ -504,9 +504,9 @@ The instance_uid field is a globally unique identifier of the running instance
 of the Agent. The Agent SHOULD self-generate this identifier and make the best
 effort to avoid creating an identifier that may conflict with identifiers
 created by other Agents. The instance_uid SHOULD remain unchanged for the
-lifetime of the Agent process. The instance_uid MUST be a
-[ULID](https://github.com/ulid/spec) formatted as a 26 character string in canonical
-representation.
+lifetime of the Agent process. The instance_uid MUST be
+16 bytes long and SHOULD be generated using
+[UUID v7 spec](https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bis-14.html#name-uuid-version-7).
 
 In case the Agent wants to use an identifier generated by the Server, the field
 SHOULD be set with a temporary value and RequestInstanceUid flag MUST be set.
@@ -704,7 +704,7 @@ The ServerToAgent message has the following structure:
 
 ```protobuf
 message ServerToAgent {
-    string instance_uid = 1;
+    bytes instance_uid = 1;
     ServerErrorResponse error_response = 2;
     AgentRemoteConfig remote_config = 3;
     ConnectionSettingsOffers connection_settings = 4; // Status: [Beta]
@@ -826,12 +826,12 @@ enum ServerCapabilities {
 Properties related to identification of the Agent, which can be overridden by the
 Server if needed. When new_instance_uid is set, Agent MUST update instance_uid
 to the value provided and use it for all further communication. The new_instance_uid MUST
-be a [ULID](https://github.com/ulid/spec) formatted as a 26 character string in canonical
-representation.
+be 16 bytes long and SHOULD be generated using
+[UUID v7 spec](https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bis-14.html#name-uuid-version-7).
 
 ```protobuf
 message AgentIdentification {
-  string new_instance_uid = 1;
+  bytes new_instance_uid = 1;
 }
 ```