diff --git a/services/xai_service.py b/services/xai_service.py
new file mode 100644
index 0000000..479f9df
--- /dev/null
+++ b/services/xai_service.py
@@ -0,0 +1,177 @@
+"""xAI Files & Collections Service"""
+import os
+import aiohttp
+import logging
+from typing import Optional, List
+
+logger = logging.getLogger(__name__)
+
+XAI_FILES_URL = "https://api.x.ai"
+XAI_MANAGEMENT_URL = "https://management-api.x.ai"
+
+
+class XAIService:
+    """
+    Client für xAI Files API und Collections Management API.
+
+    Benötigte Umgebungsvariablen:
+    - XAI_API_KEY         – regulärer API-Key für File-Uploads (api.x.ai)
+    - XAI_MANAGEMENT_KEY  – Management-API-Key für Collection-Operationen (management-api.x.ai)
+    """
+
+    def __init__(self, ctx=None):
+        self.api_key = os.getenv('XAI_API_KEY', '')
+        self.management_key = os.getenv('XAI_MANAGEMENT_KEY', '')
+        self.ctx = ctx
+        self._session: Optional[aiohttp.ClientSession] = None
+
+        if not self.api_key:
+            raise ValueError("XAI_API_KEY not configured in environment")
+        if not self.management_key:
+            raise ValueError("XAI_MANAGEMENT_KEY not configured in environment")
+
+    def _log(self, msg: str, level: str = 'info') -> None:
+        if self.ctx:
+            getattr(self.ctx.logger, level, self.ctx.logger.info)(msg)
+        else:
+            getattr(logger, level, logger.info)(msg)
+
+    async def _get_session(self) -> aiohttp.ClientSession:
+        if self._session is None or self._session.closed:
+            self._session = aiohttp.ClientSession(
+                timeout=aiohttp.ClientTimeout(total=120)
+            )
+        return self._session
+
+    async def close(self) -> None:
+        if self._session and not self._session.closed:
+            await self._session.close()
+
+    async def upload_file(
+        self,
+        file_content: bytes,
+        filename: str,
+        mime_type: str = 'application/octet-stream'
+    ) -> str:
+        """
+        Lädt eine Datei zur xAI Files API hoch (multipart/form-data).
+
+        POST https://api.x.ai/v1/files
+
+        Returns:
+            xAI file_id (str)
+
+        Raises:
+            RuntimeError: bei HTTP-Fehler oder fehlendem file_id in der Antwort
+        """
+        self._log(f"📤 Uploading {len(file_content)} bytes to xAI: {filename}")
+
+        session = await self._get_session()
+        url = f"{XAI_FILES_URL}/v1/files"
+        headers = {"Authorization": f"Bearer {self.api_key}"}
+
+        form = aiohttp.FormData()
+        form.add_field('file', file_content, filename=filename, content_type=mime_type)
+
+        async with session.post(url, data=form, headers=headers) as response:
+            try:
+                data = await response.json()
+            except Exception:
+                raw = await response.text()
+                data = {"_raw": raw}
+
+            if response.status not in (200, 201):
+                raise RuntimeError(
+                    f"xAI file upload failed ({response.status}): {data}"
+                )
+
+            file_id = data.get('id') or data.get('file_id')
+            if not file_id:
+                raise RuntimeError(
+                    f"No file_id in xAI upload response: {data}"
+                )
+
+        self._log(f"✅ xAI file uploaded: {file_id}")
+        return file_id
+
+    async def add_to_collection(self, collection_id: str, file_id: str) -> None:
+        """
+        Fügt eine Datei einer xAI-Collection hinzu.
+
+        POST https://management-api.x.ai/v1/collections/{collection_id}/documents/{file_id}
+
+        Raises:
+            RuntimeError: bei HTTP-Fehler
+        """
+        self._log(f"📚 Adding file {file_id} to collection {collection_id}")
+
+        session = await self._get_session()
+        url = f"{XAI_MANAGEMENT_URL}/v1/collections/{collection_id}/documents/{file_id}"
+        headers = {
+            "Authorization": f"Bearer {self.management_key}",
+            "Content-Type": "application/json",
+        }
+
+        async with session.post(url, headers=headers) as response:
+            if response.status not in (200, 201):
+                raw = await response.text()
+                raise RuntimeError(
+                    f"Failed to add file to collection {collection_id} ({response.status}): {raw}"
+                )
+
+        self._log(f"✅ File {file_id} added to collection {collection_id}")
+
+    async def remove_from_collection(self, collection_id: str, file_id: str) -> None:
+        """
+        Entfernt eine Datei aus einer xAI-Collection.
+        Die Datei selbst wird NICHT gelöscht – sie kann in anderen Collections sein.
+
+        DELETE https://management-api.x.ai/v1/collections/{collection_id}/documents/{file_id}
+
+        Raises:
+            RuntimeError: bei HTTP-Fehler
+        """
+        self._log(f"🗑️  Removing file {file_id} from collection {collection_id}")
+
+        session = await self._get_session()
+        url = f"{XAI_MANAGEMENT_URL}/v1/collections/{collection_id}/documents/{file_id}"
+        headers = {"Authorization": f"Bearer {self.management_key}"}
+
+        async with session.delete(url, headers=headers) as response:
+            if response.status not in (200, 204):
+                raw = await response.text()
+                raise RuntimeError(
+                    f"Failed to remove file from collection {collection_id} ({response.status}): {raw}"
+                )
+
+        self._log(f"✅ File {file_id} removed from collection {collection_id}")
+
+    async def add_to_collections(self, collection_ids: List[str], file_id: str) -> List[str]:
+        """
+        Fügt eine Datei zu mehreren Collections hinzu.
+
+        Returns:
+            Liste der erfolgreich hinzugefügten Collection-IDs
+        """
+        added = []
+        for collection_id in collection_ids:
+            try:
+                await self.add_to_collection(collection_id, file_id)
+                added.append(collection_id)
+            except Exception as e:
+                self._log(
+                    f"⚠️  Fehler beim Hinzufügen zu Collection {collection_id}: {e}",
+                    level='warn'
+                )
+        return added
+
+    async def remove_from_collections(self, collection_ids: List[str], file_id: str) -> None:
+        """Entfernt eine Datei aus mehreren Collections (ignoriert Fehler pro Collection)."""
+        for collection_id in collection_ids:
+            try:
+                await self.remove_from_collection(collection_id, file_id)
+            except Exception as e:
+                self._log(
+                    f"⚠️  Fehler beim Entfernen aus Collection {collection_id}: {e}",
+                    level='warn'
+                )
diff --git a/steps/vmh/document_sync_event_step.py b/steps/vmh/document_sync_event_step.py
index 80d88ba..6d7a2f3 100644
--- a/steps/vmh/document_sync_event_step.py
+++ b/steps/vmh/document_sync_event_step.py
@@ -13,6 +13,8 @@ from typing import Dict, Any
 from motia import FlowContext
 from services.espocrm import EspoCRMAPI
 from services.document_sync_utils import DocumentSync
+from services.xai_service import XAIService
+import hashlib
 import json
 import redis
 import os
@@ -65,10 +67,7 @@ async def handler(event_data: Dict[str, Any], ctx: FlowContext[Any]):
     # APIs initialisieren
     espocrm = EspoCRMAPI()
     sync_utils = DocumentSync(espocrm, redis_client, ctx)
-    
-    # TODO: xAI Service wird in nächstem Schritt hinzugefügt
-    # from services.xai_service import XAIService
-    # xai_service = XAIService(ctx)
+    xai_service = XAIService(ctx)
     
     try:
         # 1. ACQUIRE LOCK (verhindert parallele Syncs)
@@ -98,10 +97,10 @@ async def handler(event_data: Dict[str, Any], ctx: FlowContext[Any]):
             # 3. BESTIMME SYNC-AKTION BASIEREND AUF ACTION
             
             if action == 'delete':
-                await handle_delete(entity_id, document, sync_utils, ctx, entity_type)
+                await handle_delete(entity_id, document, sync_utils, xai_service, ctx, entity_type)
             
             elif action in ['create', 'update']:
-                await handle_create_or_update(entity_id, document, sync_utils, ctx, entity_type)
+                await handle_create_or_update(entity_id, document, sync_utils, xai_service, ctx, entity_type)
             
             else:
                 ctx.logger.warn(f"⚠️  Unbekannte Action: {action}")
@@ -138,7 +137,7 @@ async def handler(event_data: Dict[str, Any], ctx: FlowContext[Any]):
         ctx.logger.error(traceback.format_exc())
 
 
-async def handle_create_or_update(entity_id: str, document: Dict[str, Any], sync_utils: DocumentSync, ctx: FlowContext[Any], entity_type: str = 'CDokumente'):
+async def handle_create_or_update(entity_id: str, document: Dict[str, Any], sync_utils: DocumentSync, xai_service: XAIService, ctx: FlowContext[Any], entity_type: str = 'CDokumente'):
     """
     Behandelt Create/Update von Documents
     
@@ -257,62 +256,59 @@ async def handle_create_or_update(entity_id: str, document: Dict[str, Any], sync
         # ═══════════════════════════════════════════════════════════════
         # xAI SYNC DURCHFÜHREN
         # ═══════════════════════════════════════════════════════════════
-        
+
         ctx.logger.info("")
         ctx.logger.info("=" * 80)
         ctx.logger.info("🤖 xAI SYNC STARTEN")
         ctx.logger.info("=" * 80)
-        
-        # TODO: Implementierung mit xai_service.py
-        ctx.logger.warn("⚠️  xAI Service noch nicht implementiert!")
-        ctx.logger.info("")
-        ctx.logger.info("TODO: Folgende Schritte werden implementiert:")
-        ctx.logger.info("1. 📥 Download File von EspoCRM")
-        ctx.logger.info("2. 📤 Upload zu xAI (falls noch kein xaiFileId)")
-        ctx.logger.info("3. 📚 Add zu Collections")
-        ctx.logger.info("4. 💾 Update EspoCRM: xaiFileId + xaiCollections")
-        ctx.logger.info("")
-        
-        # PLACEHOLDER Implementation:
-        # 
-        # # 1. Download File von EspoCRM
-        # download_info = await sync_utils.get_document_download_info(entity_id)
-        # if not download_info:
-        #     raise Exception("Konnte Download-Info nicht ermitteln")
-        # 
-        # # 2. Upload zu xAI (falls noch nicht vorhanden)
-        # xai_file_id = document.get('xaiFileId')
-        # if not xai_file_id:
-        #     file_content = await download_file_from_espocrm(download_info)
-        #     xai_file_id = await xai_service.upload_file(file_content, download_info['filename'])
-        # 
-        # # 3. Add zu Collections
-        # for collection_id in collection_ids:
-        #     await xai_service.add_file_to_collection(collection_id, xai_file_id)
-        # 
-        # # 4. Update EspoCRM
-        # await sync_utils.release_sync_lock(
-        #     entity_id,
-        #     success=True,
-        #     extra_fields={
-        #         'xaiFileId': xai_file_id,
-        #         'xaiCollections': collection_ids
-        #     }
-        # )
-        
-        # Für jetzt: Success ohne Sync
+
+        # 1. Hole Download-Informationen (falls nicht schon aus Preview-Schritt vorhanden)
+        download_info = await sync_utils.get_document_download_info(entity_id, entity_type)
+        if not download_info:
+            raise Exception("Konnte Download-Info nicht ermitteln – Datei fehlt?")
+
+        ctx.logger.info(f"📥 Datei: {download_info['filename']} ({download_info['size']} bytes, {download_info['mime_type']})")
+
+        # 2. Download Datei von EspoCRM
+        espocrm = sync_utils.espocrm
+        file_content = await espocrm.download_attachment(download_info['attachment_id'])
+        ctx.logger.info(f"✅ Downloaded {len(file_content)} bytes")
+
+        # 3. MD5-Hash berechnen für Change-Detection
+        file_hash = hashlib.md5(file_content).hexdigest()
+        ctx.logger.info(f"🔑 MD5: {file_hash}")
+
+        # 4. Upload zu xAI
+        #    Immer neu hochladen wenn needs_sync=True (neues File oder Hash geändert)
+        ctx.logger.info("📤 Uploading to xAI...")
+        xai_file_id = await xai_service.upload_file(
+            file_content,
+            download_info['filename'],
+            download_info['mime_type']
+        )
+        ctx.logger.info(f"✅ xAI file_id: {xai_file_id}")
+
+        # 5. Zu allen Ziel-Collections hinzufügen
+        ctx.logger.info(f"📚 Füge zu {len(collection_ids)} Collection(s) hinzu...")
+        added_collections = await xai_service.add_to_collections(collection_ids, xai_file_id)
+        ctx.logger.info(f"✅ In {len(added_collections)}/{len(collection_ids)} Collections eingetragen")
+
+        # 6. EspoCRM Metadaten aktualisieren und Lock freigeben
+        await sync_utils.update_sync_metadata(
+            entity_id,
+            xai_file_id=xai_file_id,
+            collection_ids=added_collections,
+            file_hash=file_hash,
+            entity_type=entity_type
+        )
         await sync_utils.release_sync_lock(
             entity_id,
             success=True,
-            extra_fields={
-                # TODO: Echte xAI-Daten hier einsetzen
-                # 'xaiFileId': xai_file_id,
-                # 'xaiCollections': collection_ids
-            }
+            entity_type=entity_type
         )
-        
+
         ctx.logger.info("=" * 80)
-        ctx.logger.info("✅ DOCUMENT SYNC ABGESCHLOSSEN (PLACEHOLDER)")
+        ctx.logger.info("✅ DOCUMENT SYNC ABGESCHLOSSEN")
         ctx.logger.info("=" * 80)
         
     except Exception as e:
@@ -322,7 +318,7 @@ async def handle_create_or_update(entity_id: str, document: Dict[str, Any], sync
         await sync_utils.release_sync_lock(entity_id, success=False, error_message=str(e))
 
 
-async def handle_delete(entity_id: str, document: Dict[str, Any], sync_utils: DocumentSync, ctx: FlowContext[Any], entity_type: str = 'CDokumente'):
+async def handle_delete(entity_id: str, document: Dict[str, Any], sync_utils: DocumentSync, xai_service: XAIService, ctx: FlowContext[Any], entity_type: str = 'CDokumente'):
     """
     Behandelt Delete von Documents
     
@@ -346,25 +342,15 @@ async def handle_delete(entity_id: str, document: Dict[str, Any], sync_utils: Do
         ctx.logger.info(f"   xaiFileId: {xai_file_id}")
         ctx.logger.info(f"   Collections: {xai_collections}")
         
-        # TODO: Implementierung mit xai_service
-        ctx.logger.warn("⚠️  xAI Delete-Operation noch nicht implementiert!")
-        ctx.logger.info("")
-        ctx.logger.info("TODO: Folgende Schritte werden implementiert:")
-        ctx.logger.info("1. 🗑️  Remove File aus allen Collections")
-        ctx.logger.info("2. ⚠️  File NICHT von xAI löschen (kann in anderen Collections sein)")
-        ctx.logger.info("")
-        
-        # PLACEHOLDER Implementation:
-        #
-        # for collection_id in xai_collections:
-        #     await xai_service.remove_file_from_collection(collection_id, xai_file_id)
-        #
-        # ctx.logger.info(f"✅ File aus {len(xai_collections)} Collection(s) entfernt")
-        
+        ctx.logger.info(f"🗑️  Entferne aus {len(xai_collections)} Collection(s)...")
+        await xai_service.remove_from_collections(xai_collections, xai_file_id)
+        ctx.logger.info(f"✅ File aus {len(xai_collections)} Collection(s) entfernt")
+        ctx.logger.info("   (File selbst bleibt in xAI – kann in anderen Collections sein)")
+
         await sync_utils.release_sync_lock(entity_id, success=True, entity_type=entity_type)
-        
+
         ctx.logger.info("=" * 80)
-        ctx.logger.info("✅ DELETE ABGESCHLOSSEN (PLACEHOLDER)")
+        ctx.logger.info("✅ DELETE ABGESCHLOSSEN")
         ctx.logger.info("=" * 80)
         
     except Exception as e: