diff --git a/Endpoints/ApiKeysEndpoint.cs b/Endpoints/ApiKeysEndpoint.cs
index 6e8a9fe..0464834 100644
--- a/Endpoints/ApiKeysEndpoint.cs
+++ b/Endpoints/ApiKeysEndpoint.cs
@@ -540,8 +540,16 @@ public static class ApiKeysEndpoint
             return;
         }
 
-        await db.SetUserSelectedApiKey(userId, keyId);
-        await ctx.Response.WriteAsJsonAsync(new { ok = true, keyId, name = key.Name });
+        var agentId = ctx.Request.Query["agentId"].FirstOrDefault();
+        if (string.IsNullOrEmpty(agentId))
+        {
+            ctx.Response.StatusCode = 400;
+            await ctx.Response.WriteAsJsonAsync(new { error = "agentId required" });
+            return;
+        }
+
+        await db.SetAgentApiKey(userId, agentId, keyId);
+        await ctx.Response.WriteAsJsonAsync(new { ok = true, keyId, agentId, name = key.Name });
     }
 
     private static async Task HandleGetSelected(HttpContext ctx, DatabaseService db)
@@ -549,7 +557,14 @@ public static class ApiKeysEndpoint
         var userId = ctx.GetUserId();
         if (userId == null) { ctx.Response.StatusCode = 401; return; }
 
-        var key = await db.GetUserSelectedApiKey(userId);
+        var agentId = ctx.Request.Query["agentId"].FirstOrDefault();
+        if (string.IsNullOrEmpty(agentId))
+        {
+            await ctx.Response.WriteAsJsonAsync(new { selected = false });
+            return;
+        }
+
+        var key = await db.GetAgentApiKeyRecord(userId, agentId);
         if (key == null)
         {
             await ctx.Response.WriteAsJsonAsync(new { selected = false });
diff --git a/Endpoints/ChatEndpoint.cs b/Endpoints/ChatEndpoint.cs
index b51c058..a32fcc3 100644
--- a/Endpoints/ChatEndpoint.cs
+++ b/Endpoints/ChatEndpoint.cs
@@ -51,15 +51,6 @@ public static class ChatEndpoint
 
         var userId = req.HttpContext.GetUserId();
 
-        // API-Key des Users auflösen
-        var userApiKey = await db.GetUserSelectedApiKey(userId);
-        if (userApiKey == null)
-        {
-            res.StatusCode = 400;
-            await res.WriteAsJsonAsync(new { error = "Kein API-Key ausgewählt. Bitte wähle einen Key aus." });
-            return;
-        }
-
         var maxIterations = settings.GetInt("MaxIterations", 100);
 
         var hasRemote = remoteMgr.GetBySessionId(sessionId) != null;
@@ -71,6 +62,15 @@ public static class ChatEndpoint
             return;
         }
 
+        // API-Key des Users für diesen Agent auflösen
+        var userApiKey = await db.GetAgentApiKeyRecord(userId, ctx.AgentId);
+        if (userApiKey == null)
+        {
+            res.StatusCode = 400;
+            await res.WriteAsJsonAsync(new { error = "Kein API-Key für diesen Agent zugewiesen. Bitte weise einen Key zu." });
+            return;
+        }
+
         if (isChoiceResponse)
         {
             // Choice-Antwort: tool_result in die VORHERIGE Chain speichern (wo der tool_use liegt)
diff --git a/Services/CronjobService.cs b/Services/CronjobService.cs
index cb2008f..a405bb4 100644
--- a/Services/CronjobService.cs
+++ b/Services/CronjobService.cs
@@ -86,10 +86,10 @@ public class CronjobService : BackgroundService
         if (ctx == null)
             throw new Exception("Session oder Agent nicht gefunden / nicht konfiguriert");
 
-        // API-Key des Cronjob-Owners auflösen
-        var userApiKey = await _db.GetUserSelectedApiKey(job.UserId);
+        // API-Key des Cronjob-Owners für diesen Agent auflösen
+        var userApiKey = await _db.GetAgentApiKeyRecord(job.UserId, ctx.AgentId);
         if (userApiKey == null)
-            throw new Exception($"Kein API-Key für User {job.UserId} ausgewählt");
+            throw new Exception($"Kein API-Key für Agent {ctx.AgentId} zugewiesen (User {job.UserId})");
         ctx.ApiToken = userApiKey.ApiKey;
 
         // History aus DB laden
@@ -140,11 +140,11 @@ public class CronjobService : BackgroundService
                 return;
             }
 
-            // API-Key des Cronjob-Owners auflösen
-            var notifyApiKey = await _db.GetUserSelectedApiKey(job.UserId);
+            // API-Key des Cronjob-Owners für Notify-Agent auflösen
+            var notifyApiKey = await _db.GetAgentApiKeyRecord(job.UserId, notifyCtx.AgentId);
             if (notifyApiKey == null)
             {
-                _logger.LogWarning("Kein API-Key für User {UserId} (Cronjob '{Name}' Notification)", job.UserId, job.Name);
+                _logger.LogWarning("Kein API-Key für Agent {AgentId} (Cronjob '{Name}' Notification)", notifyCtx.AgentId, job.Name);
                 return;
             }
             notifyCtx.ApiToken = notifyApiKey.ApiKey;
diff --git a/Services/DatabaseService.Integrations.cs b/Services/DatabaseService.Integrations.cs
index 9f54dce..67c4a28 100644
--- a/Services/DatabaseService.Integrations.cs
+++ b/Services/DatabaseService.Integrations.cs
@@ -427,9 +427,9 @@ public partial class DatabaseService
         await conn.ExecuteAsync(
             "UPDATE scanned_keys SET adopted_api_key_id = NULL WHERE adopted_api_key_id = @keyId",
             new { keyId });
-        // User die diesen Key ausgewählt haben zurücksetzen
+        // Agent-Key-Zuordnungen die auf diesen Key verweisen löschen
         await conn.ExecuteAsync(
-            "UPDATE users SET selected_api_key_id = NULL WHERE selected_api_key_id = @keyId",
+            "DELETE FROM agent_api_keys WHERE key_id = @keyId",
             new { keyId });
         await conn.ExecuteAsync("DELETE FROM api_keys WHERE key_id = @keyId", new { keyId });
     }
diff --git a/Services/DatabaseService.Users.cs b/Services/DatabaseService.Users.cs
index a49baa8..89dc027 100644
--- a/Services/DatabaseService.Users.cs
+++ b/Services/DatabaseService.Users.cs
@@ -187,32 +187,43 @@ public partial class DatabaseService
         await conn.ExecuteAsync("DELETE FROM users WHERE user_id = @userId", new { userId });
     }
 
-    // ── User API-Key Auswahl ──
+    // ── Agent API-Key Zuordnung ──
 
-    public async Task SetUserSelectedApiKey(string userId, string keyId)
+    public async Task SetAgentApiKey(string userId, string agentId, string keyId)
     {
         using var conn = CreateConnection();
-        await conn.ExecuteAsync(
-            "UPDATE users SET selected_api_key_id = @keyId, updated_at = @now WHERE user_id = @userId",
-            new { userId, keyId = (object)keyId ?? DBNull.Value, now = DateTime.UtcNow.ToString("o") });
+        if (string.IsNullOrEmpty(keyId))
+        {
+            await conn.ExecuteAsync(
+                "DELETE FROM agent_api_keys WHERE user_id = @userId AND agent_id = @agentId",
+                new { userId, agentId });
+        }
+        else
+        {
+            await conn.ExecuteAsync(@"
+                INSERT INTO agent_api_keys (user_id, agent_id, key_id)
+                VALUES (@userId, @agentId, @keyId)
+                ON CONFLICT(user_id, agent_id) DO UPDATE SET key_id = @keyId",
+                new { userId, agentId, keyId });
+        }
     }
 
-    public async Task<string> GetUserSelectedApiKeyId(string userId)
+    public async Task<string> GetAgentApiKeyId(string userId, string agentId)
     {
         using var conn = CreateConnection();
         return await conn.QuerySingleOrDefaultAsync<string>(
-            "SELECT selected_api_key_id FROM users WHERE user_id = @userId",
-            new { userId });
+            "SELECT key_id FROM agent_api_keys WHERE user_id = @userId AND agent_id = @agentId",
+            new { userId, agentId });
     }
 
-    public async Task<ApiKeyRecord> GetUserSelectedApiKey(string userId)
+    public async Task<ApiKeyRecord> GetAgentApiKeyRecord(string userId, string agentId)
     {
         using var conn = CreateConnection();
         return await conn.QuerySingleOrDefaultAsync<ApiKeyRecord>(@"
             SELECT k.* FROM api_keys k
-            INNER JOIN users u ON u.selected_api_key_id = k.key_id
-            WHERE u.user_id = @userId",
-            new { userId });
+            INNER JOIN agent_api_keys a ON a.key_id = k.key_id
+            WHERE a.user_id = @userId AND a.agent_id = @agentId",
+            new { userId, agentId });
     }
 
     /// <summary>
diff --git a/Services/DatabaseService.cs b/Services/DatabaseService.cs
index 8b00f86..171460e 100644
--- a/Services/DatabaseService.cs
+++ b/Services/DatabaseService.cs
@@ -357,9 +357,23 @@ public partial class DatabaseService
         TryAddColumn(conn, "api_keys", "source_url", "TEXT");
         TryAddColumn(conn, "api_keys", "is_public", "INTEGER NOT NULL DEFAULT 0");
 
-        // users: ausgewählter API-Key
+        // users: ausgewählter API-Key (legacy, wird durch agent_api_keys ersetzt)
         TryAddColumn(conn, "users", "selected_api_key_id", "TEXT");
 
+        conn.Execute(@"
+            CREATE TABLE IF NOT EXISTS agent_api_keys (
+                id        INTEGER PRIMARY KEY AUTOINCREMENT,
+                user_id   TEXT NOT NULL,
+                agent_id  TEXT NOT NULL,
+                key_id    TEXT NOT NULL,
+                UNIQUE(user_id, agent_id)
+            );
+            CREATE INDEX IF NOT EXISTS idx_agent_api_keys_user ON agent_api_keys(user_id);
+        ");
+
+        // Migration: selected_api_key_id → agent_api_keys (einmalig)
+        MigrateSelectedApiKeysToAgentKeys(conn);
+
         // Migration: Bestehende PNG/JPEG-Avatare/Images zu WebP konvertieren
         MigrateImagesToWebP(conn);
 
@@ -367,6 +381,43 @@ public partial class DatabaseService
         MigrateImageThumbnails(conn);
     }
 
+    private void MigrateSelectedApiKeysToAgentKeys(SqliteConnection conn)
+    {
+        // Nur migrieren wenn agent_api_keys leer ist und users mit selected_api_key_id existieren
+        var count = conn.ExecuteScalar<int>("SELECT COUNT(*) FROM agent_api_keys");
+        if (count > 0) return;
+
+        var usersWithKeys = conn.Query<(string UserId, string SelectedApiKeyId)>(
+            "SELECT user_id, selected_api_key_id FROM users WHERE selected_api_key_id IS NOT NULL AND selected_api_key_id != ''")
+            .ToList();
+
+        foreach (var (userId, keyId) in usersWithKeys)
+        {
+            // Alle Agents des Users + öffentliche Agents
+            var agentIds = conn.Query<string>(
+                "SELECT agent_id FROM agents WHERE user_id = @userId OR is_public = 1",
+                new { userId }).ToList();
+
+            // Alle Sessions des Users mit Agent → deren Agents auch berücksichtigen
+            var sessionAgentIds = conn.Query<string>(
+                "SELECT DISTINCT agent_id FROM sessions WHERE user_id = @userId AND agent_id IS NOT NULL AND agent_id != ''",
+                new { userId }).ToList();
+
+            var allAgentIds = agentIds.Union(sessionAgentIds).Distinct().ToList();
+
+            foreach (var agentId in allAgentIds)
+            {
+                try
+                {
+                    conn.Execute(
+                        "INSERT OR IGNORE INTO agent_api_keys (user_id, agent_id, key_id) VALUES (@userId, @agentId, @keyId)",
+                        new { userId, agentId, keyId });
+                }
+                catch { /* UNIQUE constraint – already exists */ }
+            }
+        }
+    }
+
     private void MigrateImagesToWebP(SqliteConnection conn)
     {
         const int webPQuality = 80;
diff --git a/Services/TelegramService.cs b/Services/TelegramService.cs
index 3618c0a..a2c6b5b 100644
--- a/Services/TelegramService.cs
+++ b/Services/TelegramService.cs
@@ -168,11 +168,11 @@ public class TelegramService
             return;
         }
 
-        // API-Key des Bot-Owners auflösen
-        var userApiKey = await _db.GetUserSelectedApiKey(botUserId);
+        // API-Key des Bot-Owners für diesen Agent auflösen
+        var userApiKey = await _db.GetAgentApiKeyRecord(botUserId, ctx.AgentId);
         if (userApiKey == null)
         {
-            await SendMessage(chatId, botToken, "❌ Kein API-Key ausgewählt. Der Bot-Besitzer muss im Web-UI einen Key auswählen.");
+            await SendMessage(chatId, botToken, "❌ Kein API-Key für diesen Agent zugewiesen. Der Bot-Besitzer muss im Web-UI einen Key zuweisen.");
             return;
         }
         ctx.ApiToken = userApiKey.ApiKey;
diff --git a/wwwroot/js/api.js b/wwwroot/js/api.js
index 6c1a7b2..02293ed 100644
--- a/wwwroot/js/api.js
+++ b/wwwroot/js/api.js
@@ -224,8 +224,8 @@ function apiToggleApiKeyPublic(id) { return _put('/api/admin/api-keys/' + id + '
 // ── User Key Selection API ──
 
 function apiGetAvailableKeys() { return _get('/api/api-keys/available', []); }
-function apiSelectApiKey(keyId) { return _put('/api/api-keys/select/' + keyId, undefined, 'Fehler beim Auswählen'); }
-function apiGetSelectedKey() { return _get('/api/api-keys/selected', null); }
+function apiSelectApiKey(keyId, agentId) { return _put('/api/api-keys/select/' + keyId + '?agentId=' + encodeURIComponent(agentId), undefined, 'Fehler beim Auswählen'); }
+function apiGetSelectedKey(agentId) { return _get('/api/api-keys/selected' + (agentId ? '?agentId=' + encodeURIComponent(agentId) : ''), null); }
 function apiDeleteApiKey(id) { return _del('/api/admin/api-keys/' + id, 'Fehler beim Löschen'); }
 function apiCheckApiKey(id) { return _post('/api/admin/api-keys/' + id + '/check', undefined, 'Fehler beim Prüfen'); }
 function apiCheckAllApiKeys() { return _post('/api/admin/api-keys/check-all', undefined, 'Fehler beim Prüfen'); }
diff --git a/wwwroot/js/pages/chat-page.js b/wwwroot/js/pages/chat-page.js
index 08dacf5..1ce0224 100644
--- a/wwwroot/js/pages/chat-page.js
+++ b/wwwroot/js/pages/chat-page.js
@@ -49,7 +49,7 @@ async function _initChatUsageBadge() {
   if (!container) return;
 
   try {
-    var selectedKey = await apiGetSelectedKey();
+    var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
     if (!selectedKey || !selectedKey.selected) {
       container.innerHTML = '';
       var noKeyBtn = document.createElement('button');
@@ -85,7 +85,7 @@ async function _refreshChatUsageBadge() {
   var container = document.getElementById('chatUsageBadge');
   if (!container || !_chatUsageKeyId) return;
   try {
-    var selectedKey = await apiGetSelectedKey();
+    var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
     if (selectedKey) _renderChatUsageBadge(container, selectedKey);
   } catch(e) { /* ignore */ }
 }
@@ -119,7 +119,7 @@ function _renderChatUsageBadge(container, key) {
       checkBtn.querySelector('i').className = 'fa fa-spinner fa-spin';
       try {
         await apiCheckApiKey(_chatUsageKeyId);
-        var selectedKey = await apiGetSelectedKey();
+        var selectedKey = await apiGetSelectedKey(getCurrentAgentId());
         if (selectedKey) _renderChatUsageBadge(container, selectedKey);
       } catch(e) {
         console.error('Key check failed:', e);
@@ -136,7 +136,7 @@ async function _showKeySwitchModal() {
   try { keys = await apiGetAvailableKeys(); } catch(e) { return; }
 
   var selectedKey = null;
-  try { selectedKey = await apiGetSelectedKey(); } catch(e) { /* ignore */ }
+  try { selectedKey = await apiGetSelectedKey(getCurrentAgentId()); } catch(e) { /* ignore */ }
   var selectedKeyId = selectedKey ? selectedKey.keyId : null;
 
   var { body, close } = _createModal('API Key wechseln', { modal: 'key-switch-modal' });
@@ -187,7 +187,7 @@ async function _showKeySwitchModal() {
       row.addEventListener('click', async function() {
         row.classList.add('loading-state');
         try {
-          await apiSelectApiKey(key.keyId);
+          await apiSelectApiKey(key.keyId, getCurrentAgentId());
           close();
           await _initChatUsageBadge();
         } catch(e) {
@@ -352,6 +352,8 @@ registerPage('chat', {
       return;
     }
 
+    currentAgentId = session.agentId;
+
     const titleEl = document.getElementById('sessionTitle');
     if (titleEl) {
       titleEl.textContent = session.name || 'Unbenannt';
@@ -605,6 +607,7 @@ registerPage('chat', {
     _chatAbandoned = true;
     stopTypingIndicator();
     setCurrentAgentName(null);
+    currentAgentId = null;
     closeEmojiPicker();
     // Usage Badge cleanup
     if (_chatUsageScrollHandler) {
diff --git a/wwwroot/js/session.js b/wwwroot/js/session.js
index 601f976..3209edb 100644
--- a/wwwroot/js/session.js
+++ b/wwwroot/js/session.js
@@ -1,7 +1,12 @@
 // ── Session State ──
 
 let currentSessionId = null;
+let currentAgentId = null;
 
 function getCurrentSessionId() {
   return currentSessionId;
 }
+
+function getCurrentAgentId() {
+  return currentAgentId;
+}