diff --git a/extensions/telegram/src/bot/helpers.test.ts b/extensions/telegram/src/bot/helpers.test.ts
index 3c8f8aefb72..c78cb595cc0 100644
--- a/extensions/telegram/src/bot/helpers.test.ts
+++ b/extensions/telegram/src/bot/helpers.test.ts
@@ -52,13 +52,26 @@ describe("resolveTelegramForumFlag", () => {
     const getChat = vi.fn(async () => ({ is_forum: true }));
     await expect(
       resolveTelegramForumFlag({
-        chatId: -100123,
+        chatId: -100789,
         chatType: "supergroup",
         isGroup: true,
         getChat,
       }),
     ).resolves.toBe(true);
-    expect(getChat).toHaveBeenCalledWith(-100123);
+    expect(getChat).toHaveBeenCalledWith(-100789);
+  });
+
+  it("reuses resolved forum metadata for later supergroup updates", async () => {
+    const getChat = vi.fn(async () => ({ is_forum: true }));
+    const params = {
+      chatId: -100456,
+      chatType: "supergroup" as const,
+      isGroup: true,
+      getChat,
+    };
+    await expect(resolveTelegramForumFlag(params)).resolves.toBe(true);
+    await expect(resolveTelegramForumFlag(params)).resolves.toBe(true);
+    expect(getChat).toHaveBeenCalledTimes(1);
   });
 
   it("returns false when forum lookup is unavailable", async () => {
@@ -67,7 +80,7 @@ describe("resolveTelegramForumFlag", () => {
     });
     await expect(
       resolveTelegramForumFlag({
-        chatId: -100123,
+        chatId: -100999,
         chatType: "supergroup",
         isGroup: true,
         getChat,
diff --git a/extensions/telegram/src/bot/helpers.ts b/extensions/telegram/src/bot/helpers.ts
index 67f43d02833..2a2f8effaed 100644
--- a/extensions/telegram/src/bot/helpers.ts
+++ b/extensions/telegram/src/bot/helpers.ts
@@ -40,6 +40,7 @@ export {
 };
 
 const TELEGRAM_GENERAL_TOPIC_ID = 1;
+const telegramForumFlagByChatId = new Map<string, boolean>();
 
 function hadUnsafeTelegramText(raw: unknown, sanitized: string): boolean {
   return typeof raw === "string" && raw.trim().length > 0 && sanitized.trim().length === 0;
@@ -71,8 +72,15 @@ export async function resolveTelegramForumFlag(params: {
   if (!params.isGroup || params.chatType !== "supergroup" || !params.getChat) {
     return false;
   }
+  const cacheKey = String(params.chatId);
+  const cached = telegramForumFlagByChatId.get(cacheKey);
+  if (cached !== undefined) {
+    return cached;
+  }
   try {
-    return extractTelegramForumFlag(await params.getChat(params.chatId)) === true;
+    const resolved = extractTelegramForumFlag(await params.getChat(params.chatId)) === true;
+    telegramForumFlagByChatId.set(cacheKey, resolved);
+    return resolved;
   } catch {
     return false;
   }