diff --git a/package.json b/package.json
index 49b1fff..57c009b 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,7 @@
 {
   "type": "module",
   "dependencies": {
+    "@anthropic-ai/tokenizer": "^0.0.4",
     "axios": "^1.10.0",
     "deepmerge": "^4.3.1",
     "dotenv": "^16.4.5",
diff --git a/src/claude/claude-kiro.js b/src/claude/claude-kiro.js
index 5df9d87..2d25800 100644
--- a/src/claude/claude-kiro.js
+++ b/src/claude/claude-kiro.js
@@ -5,6 +5,7 @@ import * as path from 'path';
 import * as os from 'os';
 import * as crypto from 'crypto';
 import { getProviderModels } from '../provider-models.js';
+import { countTokens } from '@anthropic-ai/tokenizer';
 
 const KIRO_CONSTANTS = {
     REFRESH_URL: 'https://prod.{{region}}.auth.desktop.kiro.dev/refreshToken',
@@ -936,11 +937,15 @@ async initializeAuth(forceRefresh = false) {
         
         const finalModel = MODEL_MAPPING[model] ? model : this.modelName;
         console.log(`[Kiro] Calling generateContent with model: ${finalModel}`);
+        
+        // Estimate input tokens before making the API call
+        const inputTokens = this.estimateInputTokens(requestBody);
+        
         const response = await this.callApi('', finalModel, requestBody);
 
         try {
             const { responseText, toolCalls } = this._processApiResponse(response);
-            return this.buildClaudeResponse(responseText, false, 'assistant', model, toolCalls);
+            return this.buildClaudeResponse(responseText, false, 'assistant', model, toolCalls, inputTokens);
         } catch (error) {
             console.error('[Kiro] Error in generateContent:', error);
             throw new Error(`Error processing response: ${error.message}`);
@@ -971,13 +976,16 @@ async initializeAuth(forceRefresh = false) {
         const finalModel = MODEL_MAPPING[model] ? model : this.modelName;
         console.log(`[Kiro] Calling generateContentStream with model: ${finalModel}`);
         
+        // Estimate input tokens before making the API call
+        const inputTokens = this.estimateInputTokens(requestBody);
+        
         try {
             const response = await this.streamApi('', finalModel, requestBody);
             const { responseText, toolCalls } = this._processApiResponse(response);
 
             // Pass both responseText and toolCalls to buildClaudeResponse
             // buildClaudeResponse will handle the logic of combining them into a single stream
-            for (const chunkJson of this.buildClaudeResponse(responseText, true, 'assistant', model, toolCalls)) {
+            for (const chunkJson of this.buildClaudeResponse(responseText, true, 'assistant', model, toolCalls, inputTokens)) {
                 yield chunkJson;
             }
         } catch (error) {
@@ -991,13 +999,55 @@ async initializeAuth(forceRefresh = false) {
         }
     }
 
+    /**
+     * Count tokens for a given text using Claude's official tokenizer
+     */
+    countTextTokens(text) {
+        if (!text) return 0;
+        try {
+            return countTokens(text);
+        } catch (error) {
+            // Fallback to estimation if tokenizer fails
+            console.warn('[Kiro] Tokenizer error, falling back to estimation:', error.message);
+            return Math.ceil((text || '').length / 4);
+        }
+    }
+
+    /**
+     * Calculate input tokens from request body using Claude's official tokenizer
+     */
+    estimateInputTokens(requestBody) {
+        let totalTokens = 0;
+        
+        // Count system prompt tokens
+        if (requestBody.system) {
+            const systemText = this.getContentText(requestBody.system);
+            totalTokens += this.countTextTokens(systemText);
+        }
+        
+        // Count all messages tokens
+        if (requestBody.messages && Array.isArray(requestBody.messages)) {
+            for (const message of requestBody.messages) {
+                if (message.content) {
+                    const contentText = this.getContentText(message);
+                    totalTokens += this.countTextTokens(contentText);
+                }
+            }
+        }
+        
+        // Count tools definitions tokens if present
+        if (requestBody.tools && Array.isArray(requestBody.tools)) {
+            totalTokens += this.countTextTokens(JSON.stringify(requestBody.tools));
+        }
+        
+        return totalTokens;
+    }
+
     /**
      * Build Claude compatible response object
      */
-    buildClaudeResponse(content, isStream = false, role = 'assistant', model, toolCalls = null) {
+    buildClaudeResponse(content, isStream = false, role = 'assistant', model, toolCalls = null, inputTokens = 0) {
         const messageId = `${uuidv4()}`;
-        // Helper to estimate tokens (simple heuristic)
-        const estimateTokens = (text) => Math.ceil((text || '').length / 4);
 
         if (isStream) {
             // Kiro API is "pseudo-streaming", so we'll send a few events to simulate
@@ -1013,7 +1063,7 @@ async initializeAuth(forceRefresh = false) {
                     role: role,
                     model: model,
                     usage: {
-                        input_tokens: 0, // Kiro API doesn't provide this
+                        input_tokens: inputTokens,
                         output_tokens: 0 // Will be updated in message_delta
                     },
                     content: [] // Content will be streamed via content_block_delta
@@ -1050,7 +1100,7 @@ async initializeAuth(forceRefresh = false) {
                     type: "content_block_stop",
                     index: contentBlockIndex
                 });
-                totalOutputTokens += estimateTokens(content);
+                totalOutputTokens += this.countTextTokens(content);
                 // If there are tool calls, the stop reason remains "tool_use".
                 // If only content, it's "end_turn".
                 if (!toolCalls || toolCalls.length === 0) {
@@ -1098,7 +1148,7 @@ async initializeAuth(forceRefresh = false) {
                         type: "content_block_stop",
                         index: index
                     });
-                    totalOutputTokens += estimateTokens(JSON.stringify(inputObject));
+                    totalOutputTokens += this.countTextTokens(JSON.stringify(inputObject));
                 });
                 stopReason = "tool_use"; // If there are tool calls, the stop reason is tool_use
             }
@@ -1143,7 +1193,7 @@ async initializeAuth(forceRefresh = false) {
                         name: tc.function.name,
                         input: inputObject
                     });
-                    outputTokens += estimateTokens(tc.function.arguments);
+                    outputTokens += this.countTextTokens(tc.function.arguments);
                 }
                 stopReason = "tool_use"; // Set stop_reason to "tool_use" when toolCalls exist
             } else if (content) {
@@ -1151,7 +1201,7 @@ async initializeAuth(forceRefresh = false) {
                     type: "text",
                     text: content
                 });
-                outputTokens += estimateTokens(content);
+                outputTokens += this.countTextTokens(content);
             }
 
             return {
@@ -1162,7 +1212,7 @@ async initializeAuth(forceRefresh = false) {
                 stop_reason: stopReason,
                 stop_sequence: null,
                 usage: {
-                    input_tokens: 0, // Kiro API doesn't provide this
+                    input_tokens: inputTokens,
                     output_tokens: outputTokens
                 },
                 content: contentArray