diff --git a/CHANGELOG.md b/CHANGELOG.md
index dc38707cd..36155416c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@ Docs: https://docs.clawd.bot
 
 ### Fixes
 - Control UI: ignore bootstrap identity placeholder text for avatar values and fall back to the default avatar. https://docs.clawd.bot/cli/agents https://docs.clawd.bot/web/control-ui
+- Slack: remove deprecated `filetype` field from `files.uploadV2` to eliminate API warnings. (#1447)
 
 ## 2026.1.21
 
diff --git a/src/slack/send.ts b/src/slack/send.ts
index 1f867e9ac..cfc6c4707 100644
--- a/src/slack/send.ts
+++ b/src/slack/send.ts
@@ -94,7 +94,7 @@ async function uploadSlackFile(params: {
     file: buffer,
     filename: fileName,
     ...(params.caption ? { initial_comment: params.caption } : {}),
-    ...(contentType ? { filetype: contentType } : {}),
+    // Note: filetype is deprecated in files.uploadV2, Slack auto-detects from file content
   };
   const payload: FilesUploadV2Arguments = params.threadTs
     ? { ...basePayload, thread_ts: params.threadTs }