diff --git a/docs/channels/slack.md b/docs/channels/slack.md
index afb6a219b5c7..a882319d9fec 100644
--- a/docs/channels/slack.md
+++ b/docs/channels/slack.md
@@ -1282,7 +1282,7 @@ Primary reference: [Configuration reference - Slack](/gateway/config-channels#sl
 - channel access: `groupPolicy`, `channels.*`, `channels.*.users`, `channels.*.requireMention`
 - threading/history: `replyToMode`, `replyToModeByChatType`, `thread.*`, `historyLimit`, `dmHistoryLimit`, `dms.*.historyLimit`
 - delivery: `textChunkLimit`, `chunkMode`, `mediaMaxMb`, `streaming`, `streaming.nativeTransport`, `streaming.preview.toolProgress`
-- unfurls: `unfurlLinks`, `unfurlMedia` for `chat.postMessage` link/media preview control
+- unfurls: `unfurlLinks` (default: `false`), `unfurlMedia` for `chat.postMessage` link/media preview control
 - ops/features: `configWrites`, `commands.native`, `slashCommand.*`, `actions.*`, `userToken`, `userTokenReadOnly`
 
 </Accordion>
diff --git a/extensions/slack/src/send.ts b/extensions/slack/src/send.ts
index 36fd7110737b..6b3985690524 100644
--- a/extensions/slack/src/send.ts
+++ b/extensions/slack/src/send.ts
@@ -128,7 +128,10 @@ function hasCustomIdentity(identity?: SlackSendIdentity): boolean {
 
 function buildSlackUnfurlPayload(options?: SlackUnfurlOptions) {
   return {
-    ...(typeof options?.unfurlLinks === "boolean" ? { unfurl_links: options.unfurlLinks } : {}),
+    // Default unfurl_links to false so bot messages don't expand inline
+    // link previews (Slack message links, URLs, etc.) unless the operator
+    // explicitly opts in via `channels.slack.unfurlLinks: true`.
+    unfurl_links: options?.unfurlLinks ?? false,
     ...(typeof options?.unfurlMedia === "boolean" ? { unfurl_media: options.unfurlMedia } : {}),
   };
 }
diff --git a/extensions/slack/src/send.unfurl.test.ts b/extensions/slack/src/send.unfurl.test.ts
index 767306c34768..bb05dc7cb850 100644
--- a/extensions/slack/src/send.unfurl.test.ts
+++ b/extensions/slack/src/send.unfurl.test.ts
@@ -47,7 +47,7 @@ function requireLastPostMessagePayload(client: SlackUnfurlTestClient) {
 }
 
 describe("sendMessageSlack unfurl controls", () => {
-  it("omits Slack unfurl flags when config is unset", async () => {
+  it("defaults unfurl_links to false when config is unset", async () => {
     const client = createSlackSendTestClient();
 
     await sendMessageSlack("channel:C123", "https://example.com", {
@@ -58,7 +58,7 @@ describe("sendMessageSlack unfurl controls", () => {
 
     expect(client.chat.postMessage).toHaveBeenCalledTimes(1);
     const payload = requirePostMessagePayload(client);
-    expect("unfurl_links" in payload).toBe(false);
+    expect(payload.unfurl_links).toBe(false);
     expect("unfurl_media" in payload).toBe(false);
   });