diff --git a/src/agents/subagent-announce.ts b/src/agents/subagent-announce.ts
index ab2fbb1140e..08797c32de0 100644
--- a/src/agents/subagent-announce.ts
+++ b/src/agents/subagent-announce.ts
@@ -1262,6 +1262,7 @@ export async function runSubagentAnnounceFlow(params: {
   wakeOnDescendantSettle?: boolean;
   signal?: AbortSignal;
   bestEffortDeliver?: boolean;
+  maxAnnounceChars?: number;
 }): Promise<boolean> {
   let didAnnounce = false;
   const expectsCompletionMessage = params.expectsCompletionMessage === true;
@@ -1488,6 +1489,16 @@ export async function runSubagentAnnounceFlow(params: {
       startedAt: params.startedAt,
       endedAt: params.endedAt,
     });
+
+    // Apply maxAnnounceChars truncation if specified
+    const TRUNCATION_MARKER = "\n\n[truncated — full output in transcript]";
+    const truncatedFindings =
+      typeof params.maxAnnounceChars === "number" &&
+      params.maxAnnounceChars >= 1 &&
+      findings.length > params.maxAnnounceChars
+        ? findings.slice(0, params.maxAnnounceChars - TRUNCATION_MARKER.length) + TRUNCATION_MARKER
+        : findings;
+
     const internalEvents: AgentInternalEvent[] = [
       {
         type: "task_completion",
@@ -1498,7 +1509,7 @@ export async function runSubagentAnnounceFlow(params: {
         taskLabel,
         status: outcome.status,
         statusLabel,
-        result: findings,
+        result: truncatedFindings,
         statsLine,
         replyInstruction,
       },
diff --git a/src/agents/subagent-registry.ts b/src/agents/subagent-registry.ts
index 3c11f1850a2..97e9eb0d866 100644
--- a/src/agents/subagent-registry.ts
+++ b/src/agents/subagent-registry.ts
@@ -666,6 +666,7 @@ function startSubagentAnnounceCleanupFlow(runId: string, entry: SubagentRunRecor
     spawnMode: entry.spawnMode,
     expectsCompletionMessage: entry.expectsCompletionMessage,
     wakeOnDescendantSettle: entry.wakeOnDescendantSettle === true,
+    maxAnnounceChars: entry.maxAnnounceChars,
   })
     .then((didAnnounce) => {
       finalizeAnnounceCleanup(didAnnounce);
@@ -1349,6 +1350,7 @@ export function registerSubagentRun(params: {
   runTimeoutSeconds?: number;
   expectsCompletionMessage?: boolean;
   spawnMode?: "run" | "session";
+  maxAnnounceChars?: number;
   attachmentsDir?: string;
   attachmentsRootDir?: string;
   retainAttachmentsOnKeep?: boolean;
@@ -1388,6 +1390,10 @@ export function registerSubagentRun(params: {
     archiveAtMs,
     cleanupHandled: false,
     wakeOnDescendantSettle: undefined,
+    maxAnnounceChars:
+      typeof params.maxAnnounceChars === "number" && Number.isFinite(params.maxAnnounceChars)
+        ? Math.max(1, Math.floor(params.maxAnnounceChars))
+        : undefined,
     attachmentsDir: params.attachmentsDir,
     attachmentsRootDir: params.attachmentsRootDir,
     retainAttachmentsOnKeep: params.retainAttachmentsOnKeep,
diff --git a/src/agents/subagent-registry.types.ts b/src/agents/subagent-registry.types.ts
index 299adb83e33..da84a95f8db 100644
--- a/src/agents/subagent-registry.types.ts
+++ b/src/agents/subagent-registry.types.ts
@@ -60,4 +60,6 @@ export type SubagentRunRecord = {
   attachmentsDir?: string;
   attachmentsRootDir?: string;
   retainAttachmentsOnKeep?: boolean;
+  /** Maximum character limit for announce message delivery (truncates with marker if exceeded). */
+  maxAnnounceChars?: number;
 };
diff --git a/src/agents/subagent-spawn.ts b/src/agents/subagent-spawn.ts
index d75a8717a22..509ee6839ef 100644
--- a/src/agents/subagent-spawn.ts
+++ b/src/agents/subagent-spawn.ts
@@ -62,6 +62,7 @@ export type SpawnSubagentParams = {
   cleanup?: "delete" | "keep";
   sandbox?: SpawnSubagentSandboxMode;
   expectsCompletionMessage?: boolean;
+  maxAnnounceChars?: number;
   attachments?: Array<{
     name: string;
     content: string;
@@ -753,6 +754,7 @@ export async function spawnSubagentDirect(
       runTimeoutSeconds,
       expectsCompletionMessage,
       spawnMode,
+      maxAnnounceChars: params.maxAnnounceChars,
       attachmentsDir: attachmentAbsDir,
       attachmentsRootDir: attachmentRootDir,
       retainAttachmentsOnKeep: retainOnSessionKeep,
diff --git a/src/agents/tools/sessions-spawn-tool.ts b/src/agents/tools/sessions-spawn-tool.ts
index b735084d2b0..1aa2f9b19a3 100644
--- a/src/agents/tools/sessions-spawn-tool.ts
+++ b/src/agents/tools/sessions-spawn-tool.ts
@@ -63,6 +63,13 @@ const SessionsSpawnToolSchema = Type.Object({
       mountPath: Type.Optional(Type.String()),
     }),
   ),
+  maxAnnounceChars: Type.Optional(
+    Type.Number({
+      minimum: 1,
+      description:
+        "Maximum character limit for the sub-agent completion announce message. If exceeded, the message is truncated with a marker.",
+    }),
+  ),
 });
 
 export function createSessionsSpawnTool(
@@ -81,7 +88,7 @@ export function createSessionsSpawnTool(
     label: "Sessions",
     name: "sessions_spawn",
     description:
-      'Spawn an isolated session (runtime="subagent" or runtime="acp"). mode="run" is one-shot and mode="session" is persistent/thread-bound. Subagents inherit the parent workspace directory automatically.',
+      'Spawn an isolated session (runtime="subagent" or runtime="acp"). mode="run" is one-shot and mode="session" is persistent/thread-bound. Subagents inherit the parent workspace directory automatically. Use maxAnnounceChars to limit completion message length for platforms with character limits (e.g., Telegram 4096 chars).',
     parameters: SessionsSpawnToolSchema,
     execute: async (_toolCallId, args) => {
       const params = args as Record<string, unknown>;
@@ -118,6 +125,10 @@ export function createSessionsSpawnTool(
           ? Math.max(0, Math.floor(timeoutSecondsCandidate))
           : undefined;
       const thread = params.thread === true;
+      const maxAnnounceCharsCandidate =
+        typeof params.maxAnnounceChars === "number" && Number.isFinite(params.maxAnnounceChars)
+          ? Math.max(1, Math.floor(params.maxAnnounceChars))
+          : undefined;
       const attachments = Array.isArray(params.attachments)
         ? (params.attachments as Array<{
             name: string;
@@ -186,6 +197,7 @@ export function createSessionsSpawnTool(
           cleanup,
           sandbox,
           expectsCompletionMessage: true,
+          maxAnnounceChars: maxAnnounceCharsCandidate,
           attachments,
           attachMountPath:
             params.attachAs && typeof params.attachAs === "object"
diff --git a/src/auto-reply/reply/dispatch-acp.ts b/src/auto-reply/reply/dispatch-acp.ts
index 8fc7110fc4c..7fba9c6d28b 100644
--- a/src/auto-reply/reply/dispatch-acp.ts
+++ b/src/auto-reply/reply/dispatch-acp.ts
@@ -314,7 +314,7 @@ export async function tryDispatchAcpReply(params: {
     await projector.flush(true);
     const ttsMode = resolveTtsConfig(params.cfg).mode ?? "final";
     const accumulatedBlockText = delivery.getAccumulatedBlockText();
-    if (ttsMode === "final" && delivery.getBlockCount() > 0 && accumulatedBlockText.trim()) {
+    if (ttsMode === "final" && accumulatedBlockText.trim()) {
       try {
         const ttsSyntheticReply = await maybeApplyTtsToPayload({
           payload: { text: accumulatedBlockText },