diff --git a/clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/State.generated.cs b/clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/State.generated.cs
index 73079cc0..c2f7fa83 100644
--- a/clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/State.generated.cs
+++ b/clients/dotnet/src/AgentHostProtocol.Abstractions/Generated/State.generated.cs
@@ -2011,6 +2011,14 @@ public sealed record SessionChatSummary
     /// chat is not archived.</summary>
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public bool? Archived { get; init; }
+
+    /// <summary>Aggregate summary of file changes associated with this chat.
+    ///
+    /// Servers may populate this so session lists can show per-chat change
+    /// counts without subscribing to the session or chat channel. Updates travel
+    /// with the rest of the catalog in `root/sessionSummaryChanged`.</summary>
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public ChangesSummary? Changes { get; init; }
 }
 
 /// <summary>Aggregate counts describing the file changes associated with a session or
diff --git a/clients/go/ahptypes/state.generated.go b/clients/go/ahptypes/state.generated.go
index fb84f563..5516b942 100644
--- a/clients/go/ahptypes/state.generated.go
+++ b/clients/go/ahptypes/state.generated.go
@@ -1219,6 +1219,12 @@ type SessionChatSummary struct {
 	// lists without subscribing to the session channel. Absence means the
 	// chat is not archived.
 	Archived *bool `json:"archived,omitempty"`
+	// Aggregate summary of file changes associated with this chat.
+	//
+	// Servers may populate this so session lists can show per-chat change
+	// counts without subscribing to the session or chat channel. Updates travel
+	// with the rest of the catalog in `root/sessionSummaryChanged`.
+	Changes *ChangesSummary `json:"changes,omitempty"`
 }
 
 // Aggregate counts describing the file changes associated with a session or
diff --git a/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt b/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt
index 8fb7f0a4..55ee9ffd 100644
--- a/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt
+++ b/clients/kotlin/src/main/kotlin/com/microsoft/agenthostprotocol/generated/State.generated.kt
@@ -2179,7 +2179,15 @@ data class SessionChatSummary(
      * lists without subscribing to the session channel. Absence means the
      * chat is not archived.
      */
-    val archived: Boolean? = null
+    val archived: Boolean? = null,
+    /**
+     * Aggregate summary of file changes associated with this chat.
+     *
+     * Servers may populate this so session lists can show per-chat change
+     * counts without subscribing to the session or chat channel. Updates travel
+     * with the rest of the catalog in `root/sessionSummaryChanged`.
+     */
+    val changes: ChangesSummary? = null
 )
 
 @Serializable
diff --git a/clients/rust/crates/ahp-types/src/state.rs b/clients/rust/crates/ahp-types/src/state.rs
index 99547d09..6175e861 100644
--- a/clients/rust/crates/ahp-types/src/state.rs
+++ b/clients/rust/crates/ahp-types/src/state.rs
@@ -2470,6 +2470,13 @@ pub struct SessionChatSummary {
     /// chat is not archived.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub archived: Option<bool>,
+    /// Aggregate summary of file changes associated with this chat.
+    ///
+    /// Servers may populate this so session lists can show per-chat change
+    /// counts without subscribing to the session or chat channel. Updates travel
+    /// with the rest of the catalog in `root/sessionSummaryChanged`.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub changes: Option<ChangesSummary>,
 }
 
 /// Aggregate counts describing the file changes associated with a session or
diff --git a/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift b/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift
index 6293a123..3a23761d 100644
--- a/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift
+++ b/clients/swift/AgentHostProtocol/Sources/AgentHostProtocol/Generated/State.generated.swift
@@ -2297,19 +2297,27 @@ public struct SessionChatSummary: Codable, Sendable {
     /// lists without subscribing to the session channel. Absence means the
     /// chat is not archived.
     public var archived: Bool?
+    /// Aggregate summary of file changes associated with this chat.
+    ///
+    /// Servers may populate this so session lists can show per-chat change
+    /// counts without subscribing to the session or chat channel. Updates travel
+    /// with the rest of the catalog in `root/sessionSummaryChanged`.
+    public var changes: ChangesSummary?
 
     public init(
         resource: String,
         title: String,
         origin: ChatOrigin? = nil,
         interactivity: ChatInteractivity? = nil,
-        archived: Bool? = nil
+        archived: Bool? = nil,
+        changes: ChangesSummary? = nil
     ) {
         self.resource = resource
         self.title = title
         self.origin = origin
         self.interactivity = interactivity
         self.archived = archived
+        self.changes = changes
     }
 }
 
diff --git a/docs/.changes/20261001-session-chat-summary-changes.json b/docs/.changes/20261001-session-chat-summary-changes.json
new file mode 100644
index 00000000..ba2e78d3
--- /dev/null
+++ b/docs/.changes/20261001-session-chat-summary-changes.json
@@ -0,0 +1,4 @@
+{
+  "type": "added",
+  "message": "`SessionChatSummary.changes` exposes per-chat change counts in the lightweight chat catalog without requiring a session subscription."
+}
diff --git a/schema/actions.schema.json b/schema/actions.schema.json
index 61ca03d6..d964ec9e 100644
--- a/schema/actions.schema.json
+++ b/schema/actions.schema.json
@@ -3698,6 +3698,10 @@
         "archived": {
           "type": "boolean",
           "description": "Whether this chat has been archived independently of its owning session\n(see `chat/isArchivedChanged`).\n\nGeneric clients use this to group or filter archived chats in session\nlists without subscribing to the session channel. Absence means the\nchat is not archived."
+        },
+        "changes": {
+          "$ref": "#/$defs/ChangesSummary",
+          "description": "Aggregate summary of file changes associated with this chat.\n\nServers may populate this so session lists can show per-chat change\ncounts without subscribing to the session or chat channel. Updates travel\nwith the rest of the catalog in `root/sessionSummaryChanged`."
         }
       },
       "required": [
diff --git a/schema/commands.schema.json b/schema/commands.schema.json
index 177cf399..62a11f8f 100644
--- a/schema/commands.schema.json
+++ b/schema/commands.schema.json
@@ -2964,6 +2964,10 @@
         "archived": {
           "type": "boolean",
           "description": "Whether this chat has been archived independently of its owning session\n(see `chat/isArchivedChanged`).\n\nGeneric clients use this to group or filter archived chats in session\nlists without subscribing to the session channel. Absence means the\nchat is not archived."
+        },
+        "changes": {
+          "$ref": "#/$defs/ChangesSummary",
+          "description": "Aggregate summary of file changes associated with this chat.\n\nServers may populate this so session lists can show per-chat change\ncounts without subscribing to the session or chat channel. Updates travel\nwith the rest of the catalog in `root/sessionSummaryChanged`."
         }
       },
       "required": [
diff --git a/schema/errors.schema.json b/schema/errors.schema.json
index 981b450f..9886f386 100644
--- a/schema/errors.schema.json
+++ b/schema/errors.schema.json
@@ -1236,6 +1236,10 @@
         "archived": {
           "type": "boolean",
           "description": "Whether this chat has been archived independently of its owning session\n(see `chat/isArchivedChanged`).\n\nGeneric clients use this to group or filter archived chats in session\nlists without subscribing to the session channel. Absence means the\nchat is not archived."
+        },
+        "changes": {
+          "$ref": "#/$defs/ChangesSummary",
+          "description": "Aggregate summary of file changes associated with this chat.\n\nServers may populate this so session lists can show per-chat change\ncounts without subscribing to the session or chat channel. Updates travel\nwith the rest of the catalog in `root/sessionSummaryChanged`."
         }
       },
       "required": [
diff --git a/schema/notifications.schema.json b/schema/notifications.schema.json
index c7b6a199..608d4840 100644
--- a/schema/notifications.schema.json
+++ b/schema/notifications.schema.json
@@ -1414,6 +1414,10 @@
         "archived": {
           "type": "boolean",
           "description": "Whether this chat has been archived independently of its owning session\n(see `chat/isArchivedChanged`).\n\nGeneric clients use this to group or filter archived chats in session\nlists without subscribing to the session channel. Absence means the\nchat is not archived."
+        },
+        "changes": {
+          "$ref": "#/$defs/ChangesSummary",
+          "description": "Aggregate summary of file changes associated with this chat.\n\nServers may populate this so session lists can show per-chat change\ncounts without subscribing to the session or chat channel. Updates travel\nwith the rest of the catalog in `root/sessionSummaryChanged`."
         }
       },
       "required": [
diff --git a/schema/state.schema.json b/schema/state.schema.json
index 74b608dc..b3a94a4d 100644
--- a/schema/state.schema.json
+++ b/schema/state.schema.json
@@ -1147,6 +1147,10 @@
         "archived": {
           "type": "boolean",
           "description": "Whether this chat has been archived independently of its owning session\n(see `chat/isArchivedChanged`).\n\nGeneric clients use this to group or filter archived chats in session\nlists without subscribing to the session channel. Absence means the\nchat is not archived."
+        },
+        "changes": {
+          "$ref": "#/$defs/ChangesSummary",
+          "description": "Aggregate summary of file changes associated with this chat.\n\nServers may populate this so session lists can show per-chat change\ncounts without subscribing to the session or chat channel. Updates travel\nwith the rest of the catalog in `root/sessionSummaryChanged`."
         }
       },
       "required": [
diff --git a/types/channels-session/state.ts b/types/channels-session/state.ts
index d85c824c..cb3946dd 100644
--- a/types/channels-session/state.ts
+++ b/types/channels-session/state.ts
@@ -552,6 +552,14 @@ export interface SessionChatSummary {
    * chat is not archived.
    */
   archived?: boolean;
+  /**
+   * Aggregate summary of file changes associated with this chat.
+   *
+   * Servers may populate this so session lists can show per-chat change
+   * counts without subscribing to the session or chat channel. Updates travel
+   * with the rest of the catalog in `root/sessionSummaryChanged`.
+   */
+  changes?: ChangesSummary;
 }
 
 /**
diff --git a/types/test-cases/round-trips/051-session-chat-summary-changes-round-trip.json b/types/test-cases/round-trips/051-session-chat-summary-changes-round-trip.json
new file mode 100644
index 00000000..c7b81124
--- /dev/null
+++ b/types/test-cases/round-trips/051-session-chat-summary-changes-round-trip.json
@@ -0,0 +1,66 @@
+{
+  "name": "session-chat-summary-changes-round-trip",
+  "group": "A",
+  "description": "SessionSummary chat catalog entries preserve optional per-chat change counts so list clients can render them without subscribing to the session or chat channel.",
+  "type": "SessionSummary",
+  "input": {
+    "resource": "ahp-session:/s1",
+    "provider": "demo",
+    "title": "Agent team",
+    "status": 1,
+    "createdAt": "2024-01-01T00:00:00.001Z",
+    "modifiedAt": "2024-01-01T00:00:00.002Z",
+    "changes": {
+      "additions": 15,
+      "deletions": 4,
+      "files": 3
+    },
+    "chats": [
+      {
+        "resource": "ahp-chat:/lead",
+        "title": "Lead"
+      },
+      {
+        "resource": "ahp-chat:/worker",
+        "title": "Worker",
+        "changes": {
+          "additions": 12,
+          "deletions": 3,
+          "files": 2
+        }
+      }
+    ],
+    "defaultChat": "ahp-chat:/lead"
+  },
+  "acceptableOutputs": [
+    {
+      "resource": "ahp-session:/s1",
+      "provider": "demo",
+      "title": "Agent team",
+      "status": 1,
+      "createdAt": "2024-01-01T00:00:00.001Z",
+      "modifiedAt": "2024-01-01T00:00:00.002Z",
+      "changes": {
+        "additions": 15,
+        "deletions": 4,
+        "files": 3
+      },
+      "chats": [
+        {
+          "resource": "ahp-chat:/lead",
+          "title": "Lead"
+        },
+        {
+          "resource": "ahp-chat:/worker",
+          "title": "Worker",
+          "changes": {
+            "additions": 12,
+            "deletions": 3,
+            "files": 2
+          }
+        }
+      ],
+      "defaultChat": "ahp-chat:/lead"
+    }
+  ]
+}