diff --git a/src/main/apiServer/routes/messages.ts b/src/main/apiServer/routes/messages.ts
index 1e18c86118..bcba993915 100644
--- a/src/main/apiServer/routes/messages.ts
+++ b/src/main/apiServer/routes/messages.ts
@@ -5,6 +5,7 @@ import { getAiSdkProviderId } from '@shared/provider'
 import type { Provider } from '@types'
 import type { Request, Response } from 'express'
 import express from 'express'
+import { approximateTokenSize } from 'tokenx'
 
 import { messagesService } from '../services/messages'
 import { generateUnifiedMessage, streamUnifiedMessages } from '../services/unified-messages'
@@ -45,25 +46,34 @@ const providerRouter = express.Router({ mergeParams: true })
 
 /**
  * Estimate token count from messages
- * Simple approximation: ~4 characters per token for English text
+ * Uses tokenx library for accurate token estimation and supports images
  */
 interface CountTokensInput {
-  messages: Array<{ role: string; content: string | Array<{ type: string; text?: string }> }>
+  messages: Array<{
+    role: string
+    content:
+      | string
+      | Array<{
+          type: string
+          text?: string
+          source?: { type: string; media_type?: string; data?: string }
+        }>
+  }>
   system?: string | Array<{ type: string; text?: string }>
 }
 
 function estimateTokenCount(input: CountTokensInput): number {
   const { messages, system } = input
-  let totalChars = 0
+  let totalTokens = 0
 
-  // Count system message tokens
+  // Count system message tokens using tokenx
   if (system) {
     if (typeof system === 'string') {
-      totalChars += system.length
+      totalTokens += approximateTokenSize(system)
     } else if (Array.isArray(system)) {
       for (const block of system) {
         if (block.type === 'text' && block.text) {
-          totalChars += block.text.length
+          totalTokens += approximateTokenSize(block.text)
         }
       }
     }
@@ -72,20 +82,29 @@ function estimateTokenCount(input: CountTokensInput): number {
   // Count message tokens
   for (const msg of messages) {
     if (typeof msg.content === 'string') {
-      totalChars += msg.content.length
+      totalTokens += approximateTokenSize(msg.content)
     } else if (Array.isArray(msg.content)) {
       for (const block of msg.content) {
         if (block.type === 'text' && block.text) {
-          totalChars += block.text.length
+          totalTokens += approximateTokenSize(block.text)
+        } else if (block.type === 'image') {
+          // Image token estimation (consistent with TokenService)
+          // Base64 images: estimate from data length
+          if (block.source?.data) {
+            const dataSize = block.source.data.length * 0.75 // base64 to bytes
+            totalTokens += Math.floor(dataSize / 100)
+          } else {
+            // Default image token estimate
+            totalTokens += 1000
+          }
         }
       }
     }
-    // Add overhead for role
-    totalChars += 10
+    // Add role overhead
+    totalTokens += 3
   }
 
-  // Estimate tokens (~4 chars per token, with some overhead)
-  return Math.ceil(totalChars / 4) + messages.length * 3
+  return totalTokens
 }
 
 // Helper function for basic request validation