diff --git a/specification/v0_10/json/common_types.json b/specification/v0_10/json/common_types.json
index b8bed4ac8..3d2e6679a 100644
--- a/specification/v0_10/json/common_types.json
+++ b/specification/v0_10/json/common_types.json
@@ -9,8 +9,19 @@
       "description": "The unique identifier for a component, used for both definitions and references within the same surface."
     },
     "CallId": {
-      "type": "string",
-      "description": "The unique identifier for a server initiated function call."
+      "type": "object",
+      "description": "The unique identifier for a server initiated function call.",
+      "properties": {
+        "agentId": {
+          "type": "string",
+          "description": "Identifies the agent initiating the function call."
+        },
+        "callId": {
+          "type": "string",
+          "description": "Uniquely identifies this instance of the function call."
+        }
+      },
+      "required": ["callId"]
     },
     "AccessibilityAttributes": {
       "type": "object",
diff --git a/specification/v0_10/test/cases/call_function_message.json b/specification/v0_10/test/cases/call_function_message.json
index 5be22de0d..b90406765 100644
--- a/specification/v0_10/test/cases/call_function_message.json
+++ b/specification/v0_10/test/cases/call_function_message.json
@@ -15,7 +15,7 @@
           "returnType": "void",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "unique-call-id-123",
+        "functionCallId": { "callId": "unique-call-id-123" },
         "wantResponse": true
       }
     },
@@ -29,7 +29,7 @@
           "returnType": "void",
           "callableFrom": "remoteOnly"
         },
-        "functionCallId": "unique-call-id-123a",
+        "functionCallId": { "callId": "unique-call-id-123a" },
         "wantResponse": false
       }
     },
@@ -46,7 +46,7 @@
           "returnType": "void",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "unique-call-id-124"
+        "functionCallId": { "callId": "unique-call-id-124" }
       }
     },
     {
@@ -67,7 +67,7 @@
       "valid": false,
       "data": {
         "version": "v0.10",
-        "functionCallId": "unique-call-id-125"
+        "functionCallId": { "callId": "unique-call-id-125" }
       }
     },
     {
@@ -81,7 +81,7 @@
           "returnType": "boolean",
           "callableFrom": "clientOnly"
         },
-        "functionCallId": "unique-call-id-126"
+        "functionCallId": { "callId": "unique-call-id-126" }
       }
     },
     {
@@ -94,7 +94,7 @@
           "args": { "value": "bar" },
           "returnType": "boolean"
         },
-        "functionCallId": "unique-call-id-126b"
+        "functionCallId": { "callId": "unique-call-id-126b" }
       }
     },
     {
@@ -110,7 +110,7 @@
           "returnType": "boolean",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "unique-call-id-127"
+        "functionCallId": { "callId": "unique-call-id-127" }
       }
     },
     {
@@ -126,7 +126,7 @@
           "returnType": "boolean",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "unique-call-id-128"
+        "functionCallId": { "callId": "unique-call-id-128" }
       }
     },
     {
@@ -140,7 +140,7 @@
           "returnType": "object",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "unique-call-id-129"
+        "functionCallId": { "callId": "unique-call-id-129" }
       }
     },
     {
@@ -156,7 +156,7 @@
           "returnType": "boolean",
           "callableFrom": "clientOrRemote"
         },
-        "functionCallId": "id-3"
+        "functionCallId": { "callId": "id-3" }
       }
     }
   ]
diff --git a/specification/v0_10/test/cases/client_messages.json b/specification/v0_10/test/cases/client_messages.json
index 774e0601f..87cf3a881 100644
--- a/specification/v0_10/test/cases/client_messages.json
+++ b/specification/v0_10/test/cases/client_messages.json
@@ -50,7 +50,7 @@
         "version": "v0.10",
         "error": {
           "code": "FUNCTION_FAILED",
-          "functionCallId": "unique-call-id-132",
+          "functionCallId": { "callId": "unique-call-id-132" },
           "message": "Something went wrong"
         }
       }
@@ -62,7 +62,7 @@
         "version": "v0.10",
         "error": {
           "code": "FUNCTION_FAILED",
-          "functionCallId": "unique-call-id-133",
+          "functionCallId": { "callId": "unique-call-id-133" },
           "surfaceId": "main",
           "message": "Something went wrong"
         }
diff --git a/specification/v0_10/test/cases/function_response.json b/specification/v0_10/test/cases/function_response.json
index aa5a0a358..f8f506b5c 100644
--- a/specification/v0_10/test/cases/function_response.json
+++ b/specification/v0_10/test/cases/function_response.json
@@ -7,7 +7,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-130",
+          "functionCallId": { "callId": "unique-call-id-130" },
           "value": {
             "result": "success",
             "count": 42
@@ -33,7 +33,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131a",
+          "functionCallId": { "callId": "unique-call-id-131a" },
           "value": "success"
         }
       }
@@ -44,7 +44,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131b",
+          "functionCallId": { "callId": "unique-call-id-131b" },
           "value": 42
         }
       }
@@ -55,7 +55,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131c",
+          "functionCallId": { "callId": "unique-call-id-131c" },
           "value": true
         }
       }
@@ -66,7 +66,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131d",
+          "functionCallId": { "callId": "unique-call-id-131d" },
           "value": null
         }
       }
@@ -77,7 +77,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131e",
+          "functionCallId": { "callId": "unique-call-id-131e" },
           "value": [
             "one",
             2,
@@ -93,7 +93,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131",
+          "functionCallId": { "callId": "unique-call-id-131" },
           "value": {
             "result": { "nested": "object" }
           }
@@ -106,7 +106,7 @@
       "data": {
         "version": "v0.10",
         "functionResponse": {
-          "functionCallId": "unique-call-id-131f",
+          "functionCallId": { "callId": "unique-call-id-131f" },
           "value": [
             "one",
             {