diff --git a/Endpoints/ApiKeysEndpoint.cs b/Endpoints/ApiKeysEndpoint.cs
index 0464834..d431c2f 100644
--- a/Endpoints/ApiKeysEndpoint.cs
+++ b/Endpoints/ApiKeysEndpoint.cs
@@ -524,6 +524,22 @@ public static class ApiKeysEndpoint
         var userId = ctx.GetUserId();
         if (userId == null) { ctx.Response.StatusCode = 401; return; }
 
+        var agentId = ctx.Request.Query["agentId"].FirstOrDefault();
+        if (string.IsNullOrEmpty(agentId))
+        {
+            ctx.Response.StatusCode = 400;
+            await ctx.Response.WriteAsJsonAsync(new { error = "agentId required" });
+            return;
+        }
+
+        // "none" = Key-Zuweisung entfernen
+        if (keyId == "none")
+        {
+            await db.SetAgentApiKey(userId, agentId, null);
+            await ctx.Response.WriteAsJsonAsync(new { ok = true, keyId = (string)null, agentId, name = "Kein Key" });
+            return;
+        }
+
         var key = await db.GetApiKey(keyId);
         if (key == null)
         {
@@ -540,14 +556,6 @@ public static class ApiKeysEndpoint
             return;
         }
 
-        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 });
     }
diff --git a/Endpoints/ChatEndpoint.cs b/Endpoints/ChatEndpoint.cs
index a32fcc3..fe57dc0 100644
--- a/Endpoints/ChatEndpoint.cs
+++ b/Endpoints/ChatEndpoint.cs
@@ -62,14 +62,8 @@ public static class ChatEndpoint
             return;
         }
 
-        // API-Key des Users für diesen Agent auflösen
+        // API-Key des Users für diesen Agent auflösen (kann null sein)
         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)
         {
@@ -146,12 +140,21 @@ public static class ChatEndpoint
         // ── Preparer-Agent Phase (vor dem Worker) ──
         if (ctx.Preparer != null && !isChoiceResponse)
         {
+            var preparerApiToken = userApiKey?.ApiKey;
+            // Anthropic-Preparer braucht zwingend einen Key, OpenAI-Provider können ohne auskommen
+            if (string.IsNullOrEmpty(ctx.Preparer.Provider) && string.IsNullOrEmpty(preparerApiToken))
+            {
+                res.StatusCode = 400;
+                await res.WriteAsJsonAsync(new { error = "Kein API-Key für diesen Agent zugewiesen. Bitte weise einen Key zu." });
+                return;
+            }
+
             // Preparer bekommt History MIT seinen eigenen vorherigen Messages (Tag "preparer"),
             // damit er den Kontext seiner Rückfragen kennt
             var preparerHistory = await chatService.BuildHistoryFromDb(sessionId, includeTag: "preparer", promptBlocks: ctx.PromptBlocks);
 
             var preparerResult = await anthropic.RunPreparer(
-                res, ctx.Preparer, preparerHistory, ctx.ChainId, ctx.Workspace, sessionId, userApiKey.ApiKey, cancellationToken);
+                res, ctx.Preparer, preparerHistory, ctx.ChainId, ctx.Workspace, sessionId, preparerApiToken, cancellationToken);
 
             if (!preparerResult.ShouldForward)
             {
@@ -219,33 +222,31 @@ public static class ChatEndpoint
         {
             if (!string.IsNullOrEmpty(ctx.Provider))
             {
-                // OpenAI-kompatibler Provider – für "openai" den User-Key aus DB verwenden
-                string openAiKeyOverride = null;
-                if (ctx.Provider == "openai")
-                {
-                    // Zuerst prüfen ob der ausgewählte Key ein OpenAI-Key ist
-                    if (userApiKey.Provider == "openai")
-                        openAiKeyOverride = userApiKey.ApiKey;
-                    else
-                    {
-                        // Fallback: ersten aktiven OpenAI-Key aus DB holen
-                        openAiKeyOverride = await db.GetFirstActiveKeyByProvider("openai");
-                    }
+                // OpenAI-kompatibler Provider – Key des Users für diesen Agent verwenden
+                string openAiKeyOverride = userApiKey?.ApiKey;
 
-                    if (string.IsNullOrEmpty(openAiKeyOverride))
-                    {
-                        await SseHelper.TryWriteSse(res, "error", new { error = "Kein OpenAI API-Key vorhanden. Bitte einen OpenAI-Key in den API-Keys hinzufügen." }, sseCt);
-                        await SseHelper.TryWriteSse(res, "done", new { chainId = ctx.ChainId }, sseCt);
-                        return;
-                    }
+                // OpenAI-Provider braucht zwingend einen Key
+                if (ctx.Provider == "openai" && string.IsNullOrEmpty(openAiKeyOverride))
+                {
+                    await SseHelper.TryWriteSse(res, "error", new { error = "Kein API-Key für diesen Agent zugewiesen. Bitte einen OpenAI-Key zuweisen." }, sseCt);
+                    await SseHelper.TryWriteSse(res, "done", new { chainId = ctx.ChainId }, sseCt);
+                    return;
                 }
 
                 await openAi.StreamChat(res, ctx.ModelId, ctx.SystemPromptText, messages, ctx.ChainId, workspace: ctx.Workspace, sessionId: sessionId, agentId: ctx.AgentId, apiKeyOverride: openAiKeyOverride, workCt: workCt, sseCt: sseCt);
             }
             else
             {
-                // Standard: Anthropic
-                await anthropic.StreamChat(res, ctx.ModelId, ctx.SystemPrompt, messages, ctx.ChainId, ctx.Workspace, apiToken: userApiKey.ApiKey, sessionId: sessionId, agentId: ctx.AgentId, userId: userId, useMemory: ctx.UseMemory, webSearchVersion: ctx.WebSearchVersion, maxIterations: ctx.MaxIterations, toolChoice: effectiveToolChoice, review: ctx.Review, finalizer: ctx.Finalizer, allowUserChoice: ctx.Agent?.AllowUserChoice ?? true, planMode: ctx.PlanMode, useAutoContext: ctx.Agent?.UseAutoContext ?? true, useGitHubSearch: ctx.Agent?.UseGitHubSearch ?? false, useSerperSearch: ctx.Agent?.UseSerperSearch ?? false, workCt: workCt, hardCt: hardCt, sseCt: sseCt, remoteMgr: remoteMgr);
+                // Standard: Anthropic – Key wird zwingend benötigt
+                var anthropicToken = userApiKey?.ApiKey;
+                if (string.IsNullOrEmpty(anthropicToken))
+                {
+                    await SseHelper.TryWriteSse(res, "error", new { error = "Kein API-Key für diesen Agent zugewiesen. Bitte weise einen Key zu." }, sseCt);
+                    await SseHelper.TryWriteSse(res, "done", new { chainId = ctx.ChainId }, sseCt);
+                    return;
+                }
+
+                await anthropic.StreamChat(res, ctx.ModelId, ctx.SystemPrompt, messages, ctx.ChainId, ctx.Workspace, apiToken: anthropicToken, sessionId: sessionId, agentId: ctx.AgentId, userId: userId, useMemory: ctx.UseMemory, webSearchVersion: ctx.WebSearchVersion, maxIterations: ctx.MaxIterations, toolChoice: effectiveToolChoice, review: ctx.Review, finalizer: ctx.Finalizer, allowUserChoice: ctx.Agent?.AllowUserChoice ?? true, planMode: ctx.PlanMode, useAutoContext: ctx.Agent?.UseAutoContext ?? true, useGitHubSearch: ctx.Agent?.UseGitHubSearch ?? false, useSerperSearch: ctx.Agent?.UseSerperSearch ?? false, workCt: workCt, hardCt: hardCt, sseCt: sseCt, remoteMgr: remoteMgr);
             }
         }
         finally
diff --git a/Models/ChatContext.cs b/Models/ChatContext.cs
index ab295a6..cda5d43 100644
--- a/Models/ChatContext.cs
+++ b/Models/ChatContext.cs
@@ -36,6 +36,7 @@ public class ChatContext
 public class SubAgentContext
 {
     public string ModelId { get; set; }
+    public string Provider { get; set; }  // "" = Anthropic, "nvidia"/"openai"/etc. = OpenAI-kompatibel
     public List<object> SystemPrompt { get; set; }
     public string AgentId { get; set; }
     public string Workspace { get; set; }
diff --git a/Program.cs b/Program.cs
index b9c200c..0da72a5 100644
--- a/Program.cs
+++ b/Program.cs
@@ -96,6 +96,7 @@ builder.Services.AddSingleton<TelegramService>(sp =>
         sp.GetRequiredService<IHttpClientFactory>(),
         dbService, chatService,
         sp.GetRequiredService<AnthropicService>(),
+        sp.GetRequiredService<OpenAiService>(),
         serverSettings));
 
 // Krea Image Generation
@@ -132,6 +133,7 @@ app.Use(async (context, next) =>
 
 toolService.SetHttpClientFactory(app.Services.GetRequiredService<IHttpClientFactory>());
 app.Services.GetRequiredService<AnthropicService>().SetTelegramService(app.Services.GetRequiredService<TelegramService>());
+app.Services.GetRequiredService<AnthropicService>().SetOpenAiService(app.Services.GetRequiredService<OpenAiService>());
 await app.Services.GetRequiredService<OpenAiService>().LoadModelsAsync();
 app.UseWebSockets();
 
diff --git a/Services/AnthropicService.cs b/Services/AnthropicService.cs
index 8aaa9ab..9bcf2a4 100644
--- a/Services/AnthropicService.cs
+++ b/Services/AnthropicService.cs
@@ -50,6 +50,12 @@ public class AnthropicService
         _telegramService = telegramService;
     }
 
+    private OpenAiService _openAiService;
+    public void SetOpenAiService(OpenAiService openAiService)
+    {
+        _openAiService = openAiService;
+    }
+
     /// <summary>
     /// Liest Usage-Header aus einer Anthropic-Response und aktualisiert die api_keys-Tabelle.
     /// Fire-and-forget – Fehler werden stillschweigend ignoriert.
@@ -474,12 +480,25 @@ public class AnthropicService
         var preparerMessages = new List<object>(historyMessages);
 
         var usage = new TokenUsage();
-        var (text, iterations) = await RunAgentChat(
-            response, preparer.ModelId, preparer.SystemPrompt, preparer.AgentId,
-            preparer.Workspace, preparer.UseMemory, preparer.WebSearchVersion,
-            preparer.ToolChoice, preparerMessages, chainId, sessionId, apiToken, usage,
-            0, "preparer", preparer.Agent?.Name ?? "Vorbereiter-Agent",
-            cancellationToken, cancellationToken);
+        string text;
+        int iterations;
+
+        if (!string.IsNullOrEmpty(preparer.Provider) && _openAiService != null)
+        {
+            // OpenAI-kompatibler Preparer
+            var subCtx = BuildSubAgentChatContext(preparer, chainId, sessionId, apiToken);
+            text = await _openAiService.ChatNonStreaming(subCtx, preparerMessages);
+            iterations = 1;
+        }
+        else
+        {
+            (text, iterations) = await RunAgentChat(
+                response, preparer.ModelId, preparer.SystemPrompt, preparer.AgentId,
+                preparer.Workspace, preparer.UseMemory, preparer.WebSearchVersion,
+                preparer.ToolChoice, preparerMessages, chainId, sessionId, apiToken, usage,
+                0, "preparer", preparer.Agent?.Name ?? "Vorbereiter-Agent",
+                cancellationToken, cancellationToken);
+        }
 
         var result = new PreparerResult { IterationCount = iterations, ResponseText = text };
 
@@ -566,13 +585,24 @@ public class AnthropicService
         // Review-Agent bekommt eigene Message-History
         var reviewMessages = BuildReviewMessages(workerMessages);
 
-        // Review-Agent iteriert mit eigenen Tools
-        var (reviewText, reviewIterations) = await RunAgentChat(
-            response, review.ModelId, review.SystemPrompt, review.AgentId,
-            workspace, review.UseMemory, review.WebSearchVersion,
-            review.ToolChoice, reviewMessages, chainId, sessionId, apiToken, usage,
-            baseIterations, "review", review.Agent?.Name ?? "Review-Agent",
-            workCt, sseCt);
+        string reviewText;
+        int reviewIterations;
+
+        if (!string.IsNullOrEmpty(review.Provider) && _openAiService != null)
+        {
+            var subCtx = BuildSubAgentChatContext(review, chainId, sessionId, apiToken);
+            reviewText = await _openAiService.ChatNonStreaming(subCtx, reviewMessages);
+            reviewIterations = 1;
+        }
+        else
+        {
+            (reviewText, reviewIterations) = await RunAgentChat(
+                response, review.ModelId, review.SystemPrompt, review.AgentId,
+                workspace, review.UseMemory, review.WebSearchVersion,
+                review.ToolChoice, reviewMessages, chainId, sessionId, apiToken, usage,
+                baseIterations, "review", review.Agent?.Name ?? "Review-Agent",
+                workCt, sseCt);
+        }
 
         var result = new ReviewResult { ReviewIterationCount = reviewIterations };
 
@@ -636,12 +666,24 @@ public class AnthropicService
         // Finalizer bekommt die Konversation als Kontext (gleiche Methode wie Review)
         var finalizerMessages = BuildReviewMessages(workerMessages);
 
-        var (text, iterations) = await RunAgentChat(
-            response, finalizer.ModelId, finalizer.SystemPrompt, finalizer.AgentId,
-            finalizer.Workspace, finalizer.UseMemory, finalizer.WebSearchVersion,
-            finalizer.ToolChoice, finalizerMessages, chainId, sessionId, apiToken, usage,
-            baseIterations, "finalizer", finalizer.Agent?.Name ?? "Finalizer-Agent",
-            workCt, sseCt);
+        string text;
+        int iterations;
+
+        if (!string.IsNullOrEmpty(finalizer.Provider) && _openAiService != null)
+        {
+            var subCtx = BuildSubAgentChatContext(finalizer, chainId, sessionId, apiToken);
+            text = await _openAiService.ChatNonStreaming(subCtx, finalizerMessages);
+            iterations = 1;
+        }
+        else
+        {
+            (text, iterations) = await RunAgentChat(
+                response, finalizer.ModelId, finalizer.SystemPrompt, finalizer.AgentId,
+                finalizer.Workspace, finalizer.UseMemory, finalizer.WebSearchVersion,
+                finalizer.ToolChoice, finalizerMessages, chainId, sessionId, apiToken, usage,
+                baseIterations, "finalizer", finalizer.Agent?.Name ?? "Finalizer-Agent",
+                workCt, sseCt);
+        }
 
         await SseHelper.TryWriteSse(response, "finalizer_done", new
         {
@@ -769,6 +811,43 @@ public class AnthropicService
         return messages;
     }
 
+    /// <summary>
+    /// Baut einen ChatContext für Sub-Agents (Preparer/Review/Finalizer) auf,
+    /// wenn diese einen OpenAI-kompatiblen Provider nutzen.
+    /// </summary>
+    private ChatContext BuildSubAgentChatContext(SubAgentContext sub, string chainId, string sessionId, string apiToken)
+    {
+        // SystemPrompt als Text extrahieren (SubAgent hat List<object> mit { type, text } Blöcken)
+        var systemText = "";
+        if (sub.SystemPrompt != null)
+        {
+            var parts = new List<string>();
+            foreach (var block in sub.SystemPrompt)
+            {
+                var json = JsonSerializer.Serialize(block);
+                var el = JsonSerializer.Deserialize<JsonElement>(json);
+                if (el.TryGetProperty("text", out var t))
+                    parts.Add(t.GetString() ?? "");
+            }
+            systemText = string.Join("\n\n", parts);
+        }
+
+        return new ChatContext
+        {
+            ChainId = chainId,
+            SessionId = sessionId,
+            ModelId = sub.ModelId,
+            Provider = sub.Provider,
+            Workspace = sub.Workspace,
+            AgentId = sub.AgentId,
+            SystemPromptText = systemText,
+            UseMemory = sub.UseMemory,
+            WebSearchVersion = sub.WebSearchVersion,
+            MaxIterations = 20,
+            ApiToken = apiToken
+        };
+    }
+
     /// <summary>
     /// Generischer Agent-Chat (non-streaming für den Agent, aber SSE-Events für den Client).
     /// Wird für Review-Agent und Finalizer-Agent verwendet.
@@ -918,7 +997,7 @@ public class AnthropicService
 
                     string toolResult;
                     bool isError = false;
-                    try { toolResult = await _toolService.ExecuteTool(toolName, toolInput, agentWorkspace, _memoryService, agentId, workCt, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, telegramService: _telegramService, apiToken: apiToken); }
+                    try { toolResult = await _toolService.ExecuteTool(toolName, toolInput, agentWorkspace, _memoryService, agentId, workCt, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, openAiService: _openAiService, telegramService: _telegramService, apiToken: apiToken); }
                     catch (OperationCanceledException) { throw; }
                     catch (Exception ex) { toolResult = $"Fehler: {ex.Message}"; isError = true; }
 
@@ -1126,7 +1205,7 @@ public class AnthropicService
 
                         string toolResult;
                         bool isError = false;
-                        try { toolResult = await _toolService.ExecuteTool(toolName, toolInput, ctx.Workspace, _memoryService, ctx.AgentId, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, userId: ctx.Session?.UserId, telegramService: _telegramService, apiToken: ctx.ApiToken); }
+                        try { toolResult = await _toolService.ExecuteTool(toolName, toolInput, ctx.Workspace, _memoryService, ctx.AgentId, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, openAiService: _openAiService, userId: ctx.Session?.UserId, telegramService: _telegramService, apiToken: ctx.ApiToken); }
                         catch (OperationCanceledException) { throw; }
                         catch (Exception ex) { toolResult = $"Fehler: {ex.Message}"; isError = true; }
 
@@ -1419,7 +1498,7 @@ public class AnthropicService
 
                             string toolResult;
                             bool isError = false;
-                            try { toolResult = await _toolService.ExecuteTool(currentToolName, inputEl, workspace, _memoryService, agentId, workCt, remoteMgr: remoteMgr, sessionId: sessionId, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, userId: userId, telegramService: _telegramService, apiToken: apiToken); }
+                            try { toolResult = await _toolService.ExecuteTool(currentToolName, inputEl, workspace, _memoryService, agentId, workCt, remoteMgr: remoteMgr, sessionId: sessionId, vectorSearch: _vectorSearch, embeddingBg: _embeddingBg, db: _db, chatService: _chatService, anthropicService: this, openAiService: _openAiService, userId: userId, telegramService: _telegramService, apiToken: apiToken); }
                             catch (OperationCanceledException) { throw; }
                             catch (Exception ex) { toolResult = $"Fehler: {ex.Message}"; isError = true; }
 
diff --git a/Services/ChatService.cs b/Services/ChatService.cs
index bfcdefc..a7e3b1e 100644
--- a/Services/ChatService.cs
+++ b/Services/ChatService.cs
@@ -806,10 +806,12 @@ Für welche Plattform soll die App entwickelt werden? Web, Mobile oder Desktop?
         if (!string.IsNullOrWhiteSpace(systemText))
             prompt.Add(new { type = "text", text = systemText });
 
+        var (provider, _) = OpenAiService.ParseModelString(modelId);
         var hasTools = !string.IsNullOrEmpty(workspace) || agent.UseMemory;
         return new SubAgentContext
         {
             ModelId = modelId,
+            Provider = provider,
             SystemPrompt = prompt,
             AgentId = agent.AgentId,
             Workspace = workspace,
diff --git a/Services/CronjobService.cs b/Services/CronjobService.cs
index a405bb4..8a3f5fc 100644
--- a/Services/CronjobService.cs
+++ b/Services/CronjobService.cs
@@ -15,6 +15,7 @@ public class CronjobService : BackgroundService
     private readonly DatabaseService _db;
     private readonly ChatService _chatService;
     private readonly AnthropicService _anthropicService;
+    private readonly OpenAiService _openAiService;
     private readonly TelegramService _telegramService;
     private readonly ILogger<CronjobService> _logger;
 
@@ -22,12 +23,14 @@ public class CronjobService : BackgroundService
         DatabaseService db,
         ChatService chatService,
         AnthropicService anthropicService,
+        OpenAiService openAiService,
         TelegramService telegramService,
         ILogger<CronjobService> logger)
     {
         _db = db;
         _chatService = chatService;
         _anthropicService = anthropicService;
+        _openAiService = openAiService;
         _telegramService = telegramService;
         _logger = logger;
     }
@@ -109,8 +112,12 @@ public class CronjobService : BackgroundService
             Content = job.Prompt
         });
 
-        // Non-Streaming Chat ausführen
-        var responseText = await _anthropicService.ChatNonStreaming(ctx, history);
+        // Non-Streaming Chat ausführen – Provider-Weiche
+        string responseText;
+        if (!string.IsNullOrEmpty(ctx.Provider))
+            responseText = await _openAiService.ChatNonStreaming(ctx, history);
+        else
+            responseText = await _anthropicService.ChatNonStreaming(ctx, history);
 
         // Session-Timestamp aktualisieren
         await _db.UpdateSessionTimestamp(job.SessionId);
@@ -172,7 +179,11 @@ public class CronjobService : BackgroundService
                     ["content"] = new List<object> { new { type = "text", text = summary } }
                 }
             };
-            var notifyResponse = await _anthropicService.ChatNonStreaming(notifyCtx, notifyHistory);
+            string notifyResponse;
+            if (!string.IsNullOrEmpty(notifyCtx.Provider))
+                notifyResponse = await _openAiService.ChatNonStreaming(notifyCtx, notifyHistory);
+            else
+                notifyResponse = await _anthropicService.ChatNonStreaming(notifyCtx, notifyHistory);
 
             await _db.UpdateSessionTimestamp(job.NotifySessionId);
 
diff --git a/Services/OpenAiService.cs b/Services/OpenAiService.cs
index 909f637..4908b6d 100644
--- a/Services/OpenAiService.cs
+++ b/Services/OpenAiService.cs
@@ -732,6 +732,204 @@ public class OpenAiService
         }
     }
 
+    /// <summary>
+    /// Non-Streaming Chat für Telegram, Cronjobs und send_to_session.
+    /// Gibt den finalen Antworttext zurück. Unterstützt Tool-Calling (agentic loop).
+    /// </summary>
+    public async Task<string> ChatNonStreaming(
+        ChatContext ctx,
+        List<object> messages,
+        Func<int, Task> onIteration = null)
+    {
+        var sw = System.Diagnostics.Stopwatch.StartNew();
+        var usage = new TokenUsage();
+        int iterations = 0;
+        var finalText = new StringBuilder();
+
+        var (provider, modelId) = ParseModelString(ctx.ModelId);
+        if (!Providers.TryGetValue(provider, out var providerConfig))
+            throw new Exception($"Unbekannter Provider: '{provider}'");
+
+        // API-Key Override: User-Key hat Vorrang
+        if (!string.IsNullOrEmpty(ctx.ApiToken))
+            providerConfig = (providerConfig.BaseUrl, ctx.ApiToken);
+
+        // Gemini: Key dynamisch aus ServerSettings
+        if (provider == "gemini" && string.IsNullOrEmpty(providerConfig.ApiKey))
+            providerConfig = (providerConfig.BaseUrl, _settings.Get("GeminiApiKey"));
+
+        var chain = new ChainRecord
+        {
+            ChainId = ctx.ChainId,
+            SessionId = ctx.SessionId,
+            Model = ctx.ModelId
+        };
+
+        // Messages in OpenAI-Format konvertieren
+        var apiMessages = new List<object>();
+        if (!string.IsNullOrEmpty(ctx.SystemPromptText))
+            apiMessages.Add(new { role = "system", content = ctx.SystemPromptText });
+
+        foreach (var msg in messages)
+        {
+            var converted = ConvertMessage(msg);
+            if (converted == null) continue;
+            if (converted is List<object> toolResultList)
+            {
+                foreach (var tr in toolResultList)
+                    apiMessages.Add(tr);
+                continue;
+            }
+            apiMessages.Add(converted);
+        }
+
+        try
+        {
+            while (iterations < ctx.MaxIterations)
+            {
+                iterations++;
+                onIteration?.Invoke(iterations);
+
+                var client = CreateClient(providerConfig.ApiKey);
+                var payload = new Dictionary<string, object>
+                {
+                    ["model"] = modelId,
+                    ["messages"] = apiMessages,
+                    ["stream"] = false,
+                    ["max_tokens"] = 16384,
+                    ["tools"] = OpenAiTools,
+                    ["tool_choice"] = "auto"
+                };
+
+                var jsonPayload = JsonSerializer.Serialize(payload);
+                var httpContent = new StringContent(jsonPayload, Encoding.UTF8, "application/json");
+
+                using var httpResp = await client.SendAsync(
+                    new HttpRequestMessage(HttpMethod.Post, $"{providerConfig.BaseUrl}/chat/completions") { Content = httpContent });
+
+                var respBody = await httpResp.Content.ReadAsStringAsync();
+
+                if (!httpResp.IsSuccessStatusCode)
+                {
+                    var errMsg = $"API {(int)httpResp.StatusCode}: {respBody}";
+                    await _db.SaveMessage(new MessageRecord
+                    {
+                        ChainId = ctx.ChainId, Iteration = iterations,
+                        Role = "system", Type = "error",
+                        Content = errMsg, IsError = true
+                    });
+                    await FinalizeChain(chain, usage, iterations, "error", sw);
+                    throw new Exception($"OpenAI API Fehler: {(int)httpResp.StatusCode}");
+                }
+
+                var resp = JsonSerializer.Deserialize<JsonElement>(respBody);
+
+                // Usage tracken
+                if (resp.TryGetProperty("usage", out var usageProp))
+                {
+                    if (usageProp.TryGetProperty("prompt_tokens", out var pt))
+                        usage.InputTokens = pt.GetInt64();
+                    if (usageProp.TryGetProperty("completion_tokens", out var ct2))
+                        usage.OutputTokens = ct2.GetInt64();
+                }
+
+                // Erste Choice auswerten
+                var choices = resp.GetProperty("choices");
+                if (choices.GetArrayLength() == 0) break;
+
+                var choice = choices[0];
+                var message = choice.GetProperty("message");
+                var finishReason = choice.TryGetProperty("finish_reason", out var frProp) ? frProp.GetString() ?? "" : "";
+
+                // Text extrahieren
+                if (message.TryGetProperty("content", out var contentProp) && contentProp.ValueKind == JsonValueKind.String)
+                {
+                    var text = contentProp.GetString() ?? "";
+                    if (!string.IsNullOrEmpty(text))
+                    {
+                        finalText.Append(text);
+                        await _db.SaveMessage(new MessageRecord
+                        {
+                            ChainId = ctx.ChainId, Iteration = iterations,
+                            Role = "assistant", Type = "text",
+                            Content = text
+                        });
+                    }
+                }
+
+                // Tool-Calls prüfen
+                if (!message.TryGetProperty("tool_calls", out var toolCallsProp) || toolCallsProp.GetArrayLength() == 0)
+                {
+                    await FinalizeChain(chain, usage, iterations, "end_turn", sw);
+                    break;
+                }
+
+                // Assistant-Message mit tool_calls in History
+                var assistantMsg = JsonSerializer.Deserialize<JsonElement>(message.GetRawText());
+                apiMessages.Add(new
+                {
+                    role = "assistant",
+                    content = message.TryGetProperty("content", out var c) && c.ValueKind == JsonValueKind.String ? c.GetString() ?? "" : "",
+                    tool_calls = JsonSerializer.Deserialize<List<object>>(toolCallsProp.GetRawText())
+                });
+
+                // Tool-Calls ausführen
+                var toolResults = new List<object>();
+                foreach (var tc in toolCallsProp.EnumerateArray())
+                {
+                    var tcId = tc.GetProperty("id").GetString() ?? "";
+                    var func = tc.GetProperty("function");
+                    var tcName = func.GetProperty("name").GetString() ?? "";
+                    var tcArgs = func.TryGetProperty("arguments", out var argsProp) ? argsProp.GetString() ?? "{}" : "{}";
+
+                    await _db.SaveMessage(new MessageRecord
+                    {
+                        ChainId = ctx.ChainId, Iteration = iterations,
+                        Role = "assistant", Type = "tool_use",
+                        Content = tcArgs,
+                        ToolCallId = tcId, ToolName = tcName
+                    });
+
+                    JsonElement inputEl;
+                    try { inputEl = JsonSerializer.Deserialize<JsonElement>(tcArgs); }
+                    catch { inputEl = JsonSerializer.Deserialize<JsonElement>("{}"); }
+
+                    string toolResult;
+                    bool isError = false;
+                    try { toolResult = await _toolService.ExecuteTool(tcName, inputEl, ctx.Workspace); }
+                    catch (Exception ex) { toolResult = $"Fehler: {ex.Message}"; isError = true; }
+
+                    toolResults.Add(new
+                    {
+                        role = "tool",
+                        tool_call_id = tcId,
+                        content = toolResult
+                    });
+
+                    await _db.SaveMessage(new MessageRecord
+                    {
+                        ChainId = ctx.ChainId, Iteration = iterations,
+                        Role = "tool", Type = "tool_result",
+                        Content = toolResult,
+                        ToolCallId = tcId, ToolName = tcName,
+                        IsError = isError
+                    });
+                }
+
+                foreach (var tr in toolResults)
+                    apiMessages.Add(tr);
+            }
+        }
+        catch
+        {
+            if (iterations > 0)
+                await FinalizeChain(chain, usage, iterations, "error", sw);
+            throw;
+        }
+
+        return finalText.Length > 0 ? finalText.ToString() : "(Keine Textantwort)";
+    }
+
     /// <summary>
     /// Konvertiert eine Anthropic-format Message in das OpenAI-format.
     /// </summary>
diff --git a/Services/TelegramService.cs b/Services/TelegramService.cs
index a2c6b5b..383b5b5 100644
--- a/Services/TelegramService.cs
+++ b/Services/TelegramService.cs
@@ -15,6 +15,7 @@ public class TelegramService
     private readonly DatabaseService _db;
     private readonly ChatService _chatService;
     private readonly AnthropicService _anthropic;
+    private readonly OpenAiService _openAi;
     private readonly ServerSettingsService _settings;
 
     public TelegramService(
@@ -22,12 +23,14 @@ public class TelegramService
         DatabaseService db,
         ChatService chatService,
         AnthropicService anthropic,
+        OpenAiService openAi,
         ServerSettingsService settings)
     {
         _httpFactory = httpFactory;
         _db = db;
         _chatService = chatService;
         _anthropic = anthropic;
+        _openAi = openAi;
         _settings = settings;
     }
 
@@ -197,11 +200,23 @@ public class TelegramService
                 Content = userText
             });
 
-            var reply = await _anthropic.ChatNonStreaming(ctx, history, onIteration: async (iteration) =>
+            string reply;
+            if (!string.IsNullOrEmpty(ctx.Provider))
             {
-                if (iteration % 3 == 0)
-                    await SendChatAction(chatId, botToken, "typing");
-            });
+                reply = await _openAi.ChatNonStreaming(ctx, history, onIteration: async (iteration) =>
+                {
+                    if (iteration % 3 == 0)
+                        await SendChatAction(chatId, botToken, "typing");
+                });
+            }
+            else
+            {
+                reply = await _anthropic.ChatNonStreaming(ctx, history, onIteration: async (iteration) =>
+                {
+                    if (iteration % 3 == 0)
+                        await SendChatAction(chatId, botToken, "typing");
+                });
+            }
 
             await SendLongMessage(chatId, botToken, reply);
         }
diff --git a/Services/ToolService.cs b/Services/ToolService.cs
index 001da3d..4a04fc5 100644
--- a/Services/ToolService.cs
+++ b/Services/ToolService.cs
@@ -390,7 +390,7 @@ public class ToolService
         };
     }
 
-    public async Task<string> ExecuteTool(string name, JsonElement input, string workspace, MemoryService memoryService = null, string agentId = null, CancellationToken cancellationToken = default, RemoteConnectionManager remoteMgr = null, string sessionId = null, VectorSearchService vectorSearch = null, EmbeddingBackgroundService embeddingBg = null, DatabaseService db = null, ChatService chatService = null, AnthropicService anthropicService = null, string userId = null, TelegramService telegramService = null, string apiToken = null)
+    public async Task<string> ExecuteTool(string name, JsonElement input, string workspace, MemoryService memoryService = null, string agentId = null, CancellationToken cancellationToken = default, RemoteConnectionManager remoteMgr = null, string sessionId = null, VectorSearchService vectorSearch = null, EmbeddingBackgroundService embeddingBg = null, DatabaseService db = null, ChatService chatService = null, AnthropicService anthropicService = null, OpenAiService openAiService = null, string userId = null, TelegramService telegramService = null, string apiToken = null)
     {
         switch (name)
         {
@@ -742,7 +742,7 @@ public class ToolService
             }
             case "send_to_session":
             {
-                if (db == null || chatService == null || anthropicService == null)
+                if (db == null || chatService == null || (anthropicService == null && openAiService == null))
                     return "Fehler: send_to_session nicht verfügbar";
 
                 var sessionIdOrName = input.GetProperty("session_id_or_name").GetString() ?? "";
@@ -767,7 +767,10 @@ public class ToolService
                 var ctx = await chatService.PrepareContext(targetSessionId, userId: userId);
                 if (ctx == null)
                     return $"Fehler: Session '{targetSession.Name}' ist nicht konfiguriert (kein Agent zugewiesen?)";
-                ctx.ApiToken = apiToken;
+
+                // API-Key des Ziel-Agents auflösen (nicht den Key des aufrufenden Agents nutzen)
+                var targetApiKey = await db.GetAgentApiKeyRecord(userId, ctx.AgentId);
+                ctx.ApiToken = targetApiKey?.ApiKey ?? apiToken;
 
                 // History aufbauen – User-Message NICHT in DB speichern (wie Cronjob)
                 // Stattdessen als kontextualisierte Nachricht in die History injizieren
@@ -780,7 +783,10 @@ public class ToolService
 
                 try
                 {
-                    await anthropicService.ChatNonStreaming(ctx, history);
+                    if (!string.IsNullOrEmpty(ctx.Provider) && openAiService != null)
+                        await openAiService.ChatNonStreaming(ctx, history);
+                    else
+                        await anthropicService.ChatNonStreaming(ctx, history);
                 }
                 catch (Exception ex)
                 {
diff --git a/wwwroot/js/pages/chat-page.js b/wwwroot/js/pages/chat-page.js
index 1ce0224..f57d297 100644
--- a/wwwroot/js/pages/chat-page.js
+++ b/wwwroot/js/pages/chat-page.js
@@ -152,6 +152,36 @@ async function _showKeySwitchModal() {
   var list = document.createElement('div');
   list.className = 'key-switch-list';
 
+  // "Kein Key"-Option als erste Zeile
+  var noneRow = document.createElement('div');
+  noneRow.className = 'key-switch-row';
+  if (!selectedKeyId) noneRow.classList.add('active');
+  var noneInfo = document.createElement('div');
+  noneInfo.className = 'key-switch-info';
+  var noneName = document.createElement('div');
+  noneName.className = 'key-switch-name';
+  noneName.textContent = 'Kein Key';
+  noneInfo.appendChild(noneName);
+  var noneMeta = document.createElement('div');
+  noneMeta.className = 'key-switch-meta';
+  noneMeta.textContent = 'Agent ohne API-Key nutzen';
+  noneInfo.appendChild(noneMeta);
+  noneRow.appendChild(noneInfo);
+  if (selectedKeyId) {
+    noneRow.classList.add('clickable');
+    noneRow.addEventListener('click', async function() {
+      noneRow.classList.add('loading-state');
+      try {
+        await apiSelectApiKey('none', getCurrentAgentId());
+        close();
+        await _initChatUsageBadge();
+      } catch(e) {
+        noneRow.classList.remove('loading-state');
+      }
+    });
+  }
+  list.appendChild(noneRow);
+
   keys.forEach(function(key) {
     var row = document.createElement('div');
     row.className = 'key-switch-row';