diff --git a/apps/sim/app/api/tools/slack/ephemeral-message/route.ts b/apps/sim/app/api/tools/slack/ephemeral-message/route.ts
new file mode 100644
index 00000000000..315982fec38
--- /dev/null
+++ b/apps/sim/app/api/tools/slack/ephemeral-message/route.ts
@@ -0,0 +1,113 @@
+import { createLogger } from '@sim/logger'
+import { type NextRequest, NextResponse } from 'next/server'
+import { z } from 'zod'
+import { checkInternalAuth } from '@/lib/auth/hybrid'
+import { generateRequestId } from '@/lib/core/utils/request'
+import { openDMChannel, postSlackEphemeralMessage } from '../utils'
+
+export const dynamic = 'force-dynamic'
+
+const logger = createLogger('SlackEphemeralMessageAPI')
+
+const SlackEphemeralMessageSchema = z
+  .object({
+    accessToken: z.string().min(1, 'Access token is required'),
+    channel: z.string().optional().nullable(),
+    dmUserId: z.string().optional().nullable(),
+    userId: z.string().min(1, 'User ID is required'),
+    text: z.string().min(1, 'Message text is required'),
+    thread_ts: z.string().optional().nullable(),
+  })
+  .refine((data) => data.channel || data.dmUserId, {
+    message: 'Either channel or dmUserId is required',
+  })
+
+export async function POST(request: NextRequest) {
+  const requestId = generateRequestId()
+
+  try {
+    const authResult = await checkInternalAuth(request, { requireWorkflowId: false })
+
+    if (!authResult.success) {
+      logger.warn(`[${requestId}] Unauthorized Slack ephemeral send attempt: ${authResult.error}`)
+      return NextResponse.json(
+        {
+          success: false,
+          error: authResult.error || 'Authentication required',
+        },
+        { status: 401 }
+      )
+    }
+
+    logger.info(
+      `[${requestId}] Authenticated Slack ephemeral send request via ${authResult.authType}`,
+      {
+        userId: authResult.userId,
+      }
+    )
+
+    const body = await request.json()
+    const validatedData = SlackEphemeralMessageSchema.parse(body)
+
+    let channel = validatedData.channel
+
+    if (!channel && validatedData.dmUserId) {
+      logger.info(`[${requestId}] Opening DM channel for user: ${validatedData.dmUserId}`)
+      channel = await openDMChannel(
+        validatedData.accessToken,
+        validatedData.dmUserId,
+        requestId,
+        logger
+      )
+    }
+
+    if (!channel) {
+      return NextResponse.json(
+        { success: false, error: 'Either channel or dmUserId is required' },
+        { status: 400 }
+      )
+    }
+
+    logger.info(`[${requestId}] Sending Slack ephemeral message`, {
+      channel,
+      targetUser: validatedData.userId,
+      hasThread: !!validatedData.thread_ts,
+    })
+
+    const result = await postSlackEphemeralMessage(
+      validatedData.accessToken,
+      channel,
+      validatedData.userId,
+      validatedData.text,
+      validatedData.thread_ts
+    )
+
+    if (!result.ok) {
+      logger.error(`[${requestId}] Slack API error:`, result.error)
+      return NextResponse.json(
+        { success: false, error: result.error || 'Failed to send ephemeral message' },
+        { status: 400 }
+      )
+    }
+
+    logger.info(`[${requestId}] Ephemeral message sent successfully`)
+
+    return NextResponse.json({
+      success: true,
+      output: {
+        message_ts: result.message_ts,
+        channel,
+        user: validatedData.userId,
+      },
+    })
+  } catch (error) {
+    logger.error(`[${requestId}] Error sending Slack ephemeral message:`, error)
+    return NextResponse.json(
+      {
+        success: false,
+        error: error instanceof Error ? error.message : 'Unknown error occurred',
+      },
+      { status: 500 }
+    )
+  }
+}
diff --git a/apps/sim/app/api/tools/slack/utils.ts b/apps/sim/app/api/tools/slack/utils.ts
index b635c49d8fe..34cb8bc4333 100644
--- a/apps/sim/app/api/tools/slack/utils.ts
+++ b/apps/sim/app/api/tools/slack/utils.ts
@@ -29,6 +29,34 @@ export async function postSlackMessage(
   return response.json()
 }
 
+/**
+ * Sends an ephemeral message to a Slack channel using chat.postEphemeral
+ * Ephemeral messages are only visible to the specified user and do not persist
+ */
+export async function postSlackEphemeralMessage(
+  accessToken: string,
+  channel: string,
+  user: string,
+  text: string,
+  threadTs?: string | null
+): Promise<{ ok: boolean; message_ts?: string; error?: string }> {
+  const response = await fetch('https://slack.com/api/chat.postEphemeral', {
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      Authorization: `Bearer ${accessToken}`,
+    },
+    body: JSON.stringify({
+      channel,
+      user,
+      text,
+      ...(threadTs && { thread_ts: threadTs }),
+    }),
+  })
+
+  return response.json()
+}
+
 /**
  * Creates a default message object when the API doesn't return one
  */
diff --git a/apps/sim/tools/registry.ts b/apps/sim/tools/registry.ts
index 2bf07caeb4d..3397a700b27 100644
--- a/apps/sim/tools/registry.ts
+++ b/apps/sim/tools/registry.ts
@@ -1541,6 +1541,7 @@ import {
   slackCanvasTool,
   slackDeleteMessageTool,
   slackDownloadTool,
+  slackEphemeralMessageTool,
   slackGetMessageTool,
   slackGetThreadTool,
   slackGetUserTool,
@@ -2208,6 +2209,7 @@ export const tools: Record<string, ToolConfig> = {
   polymarket_get_holders: polymarketGetHoldersTool,
   slack_message: slackMessageTool,
   slack_message_reader: slackMessageReaderTool,
+  slack_ephemeral_message: slackEphemeralMessageTool,
   slack_list_channels: slackListChannelsTool,
   slack_list_members: slackListMembersTool,
   slack_list_users: slackListUsersTool,
diff --git a/apps/sim/tools/slack/ephemeral_message.ts b/apps/sim/tools/slack/ephemeral_message.ts
new file mode 100644
index 00000000000..d010f2bfddb
--- /dev/null
+++ b/apps/sim/tools/slack/ephemeral_message.ts
@@ -0,0 +1,111 @@
+import type { SlackEphemeralMessageParams, SlackEphemeralMessageResponse } from '@/tools/slack/types'
+import type { ToolConfig } from '@/tools/types'
+
+export const slackEphemeralMessageTool: ToolConfig<
+  SlackEphemeralMessageParams,
+  SlackEphemeralMessageResponse
+> = {
+  id: 'slack_ephemeral_message',
+  name: 'Slack Ephemeral Message',
+  description:
+    'Send ephemeral messages visible only to a specific user in Slack channels or threads. Messages are temporary and do not persist across sessions.',
+  version: '1.0.0',
+
+  oauth: {
+    required: true,
+    provider: 'slack',
+  },
+
+  params: {
+    authMethod: {
+      type: 'string',
+      required: false,
+      visibility: 'user-only',
+      description: 'Authentication method: oauth or bot_token',
+    },
+    destinationType: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Destination type: channel or dm',
+    },
+    botToken: {
+      type: 'string',
+      required: false,
+      visibility: 'user-only',
+      description: 'Bot token for Custom Bot',
+    },
+    accessToken: {
+      type: 'string',
+      required: false,
+      visibility: 'hidden',
+      description: 'OAuth access token or bot token for Slack API',
+    },
+    channel: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Slack channel ID (e.g., C1234567890)',
+    },
+    dmUserId: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Slack user ID for direct messages (e.g., U1234567890)',
+    },
+    userId: {
+      type: 'string',
+      required: true,
+      visibility: 'user-or-llm',
+      description: 'User ID who will see the ephemeral message (e.g., U1234567890)',
+    },
+    text: {
+      type: 'string',
+      required: true,
+      visibility: 'user-or-llm',
+      description: 'Message text to send (supports Slack mrkdwn formatting)',
+    },
+    threadTs: {
+      type: 'string',
+      required: false,
+      visibility: 'user-or-llm',
+      description: 'Thread timestamp to reply to (creates ephemeral thread reply)',
+    },
+  },
+
+  request: {
+    url: '/api/tools/slack/ephemeral-message',
+    method: 'POST',
+    headers: () => ({
+      'Content-Type': 'application/json',
+    }),
+    body: (params: SlackEphemeralMessageParams) => {
+      const isDM = params.destinationType === 'dm'
+      return {
+        accessToken: params.accessToken || params.botToken,
+        channel: isDM ? undefined : params.channel,
+        dmUserId: isDM ? params.dmUserId : undefined,
+        userId: params.userId,
+        text: params.text,
+        thread_ts: params.threadTs || undefined,
+      }
+    },
+  },
+
+  transformResponse: async (response: Response) => {
+    const data = await response.json()
+    if (!data.success) {
+      throw new Error(data.error || 'Failed to send Slack ephemeral message')
+    }
+    return {
+      success: true,
+      output: data.output,
+    }
+  },
+
+  outputs: {
+    message_ts: { type: 'string', description: 'Ephemeral message timestamp' },
+    channel: { type: 'string', description: 'Channel ID where message was sent' },
+    user: { type: 'string', description: 'User ID who received the ephemeral message' },
+  },
+}
diff --git a/apps/sim/tools/slack/index.ts b/apps/sim/tools/slack/index.ts
index 2bc0f249ef6..43797d51dd9 100644
--- a/apps/sim/tools/slack/index.ts
+++ b/apps/sim/tools/slack/index.ts
@@ -2,6 +2,7 @@ import { slackAddReactionTool } from '@/tools/slack/add_reaction'
 import { slackCanvasTool } from '@/tools/slack/canvas'
 import { slackDeleteMessageTool } from '@/tools/slack/delete_message'
 import { slackDownloadTool } from '@/tools/slack/download'
+import { slackEphemeralMessageTool } from '@/tools/slack/ephemeral_message'
 import { slackGetMessageTool } from '@/tools/slack/get_message'
 import { slackGetThreadTool } from '@/tools/slack/get_thread'
 import { slackGetUserTool } from '@/tools/slack/get_user'
@@ -26,4 +27,5 @@ export {
   slackGetUserTool,
   slackGetMessageTool,
   slackGetThreadTool,
+  slackEphemeralMessageTool,
 }
diff --git a/apps/sim/tools/slack/types.ts b/apps/sim/tools/slack/types.ts
index 73ecccbad11..312400534bf 100644
--- a/apps/sim/tools/slack/types.ts
+++ b/apps/sim/tools/slack/types.ts
@@ -590,6 +590,15 @@ export interface SlackGetThreadParams extends SlackBaseParams {
   limit?: number
 }
 
+export interface SlackEphemeralMessageParams extends SlackBaseParams {
+  destinationType?: 'channel' | 'dm'
+  channel?: string
+  dmUserId?: string
+  userId: string
+  text: string
+  threadTs?: string
+}
+
 export interface SlackMessageResponse extends ToolResponse {
   output: {
     // Legacy properties for backward compatibility
@@ -841,6 +850,14 @@ export interface SlackGetThreadResponse extends ToolResponse {
   }
 }
 
+export interface SlackEphemeralMessageResponse extends ToolResponse {
+  output: {
+    message_ts: string
+    channel: string
+    user: string
+  }
+}
+
 export type SlackResponse =
   | SlackCanvasResponse
   | SlackMessageReaderResponse
@@ -855,3 +872,4 @@ export type SlackResponse =
   | SlackGetUserResponse
   | SlackGetMessageResponse
   | SlackGetThreadResponse
+  | SlackEphemeralMessageResponse