diff --git a/zaban_backend/app/api/v1/language_detection.py b/zaban_backend/app/api/v1/language_detection.py
index 6f52f96..b1caaf3 100644
--- a/zaban_backend/app/api/v1/language_detection.py
+++ b/zaban_backend/app/api/v1/language_detection.py
@@ -1,10 +1,13 @@
-from fastapi import APIRouter, HTTPException, Body
+from fastapi import APIRouter, HTTPException, Body, Depends
+
+from ...core.api_key_auth import require_api_key
+
 
 router = APIRouter(prefix="")
 
 
 @router.post("/detect-language")
-async def detect_language(body: dict = Body(...)):
+async def detect_language(body: dict = Body(...), _api_key=Depends(require_api_key)):
     """
     Detect language from text using FastText.
     
diff --git a/zaban_backend/app/api/v1/stt.py b/zaban_backend/app/api/v1/stt.py
index d4cf2b3..50bc36b 100644
--- a/zaban_backend/app/api/v1/stt.py
+++ b/zaban_backend/app/api/v1/stt.py
@@ -2,10 +2,11 @@
 import logging
 
 import httpx
-from fastapi import APIRouter, HTTPException, Request
+from fastapi import APIRouter, HTTPException, Request, Depends
 from starlette.datastructures import UploadFile
 
 from ...services.ai4bharat import Ai4BharatClient
+from ...core.api_key_auth import require_api_key
 
 
 router = APIRouter(prefix="")
@@ -50,7 +51,7 @@ def _log_stt_response(response: dict, request_kind: str) -> None:
 
 
 @router.post("/stt")
-async def stt(request: Request):
+async def stt(request: Request, _api_key=Depends(require_api_key)):
     """
     Speech-to-Text: accept either multipart (audio file) or JSON (audio_url, optional lang).
     JSON: audio_url required; lang optional (auto-detect when omitted).
diff --git a/zaban_backend/app/api/v1/transliteration.py b/zaban_backend/app/api/v1/transliteration.py
index 4156284..85a4cac 100644
--- a/zaban_backend/app/api/v1/transliteration.py
+++ b/zaban_backend/app/api/v1/transliteration.py
@@ -1,8 +1,9 @@
-from fastapi import APIRouter, HTTPException
+from fastapi import APIRouter, HTTPException, Depends
 from pydantic import BaseModel
 from typing import Optional
 
 from ...services.ai4bharat import Ai4BharatClient
+from ...core.api_key_auth import require_api_key
 
 
 router = APIRouter(prefix="")
@@ -20,7 +21,7 @@ class TransliterateRequest(BaseModel):
 
 
 @router.post("/transliterate")
-async def transliterate(req: TransliterateRequest):
+async def transliterate(req: TransliterateRequest, _api_key=Depends(require_api_key)):
     try:
         return await client.transliterate(
             text=req.text,