diff --git a/Services/AnthropicService.Agents.cs b/Services/AnthropicService.Agents.cs
index d14acf8..48678d1 100644
--- a/Services/AnthropicService.Agents.cs
+++ b/Services/AnthropicService.Agents.cs
@@ -466,9 +466,24 @@ public partial class AnthropicService
             };
 
             if (systemPrompt is List<object> spBlocks && spBlocks.Count > 0)
+            {
+                // Cache-Breakpoint auf den letzten System-Prompt-Block (1h TTL).
+                ApplyCacheControlToLast(spBlocks);
                 payload["system"] = spBlocks;
+            }
             else if (systemPrompt is string spText && !string.IsNullOrEmpty(spText))
-                payload["system"] = spText;
+            {
+                // String-System-Prompt → in Block-Form mit cache_control konvertieren.
+                payload["system"] = new List<object>
+                {
+                    new Dictionary<string, object>
+                    {
+                        ["type"] = "text",
+                        ["text"] = spText,
+                        ["cache_control"] = new { type = "ephemeral", ttl = "1h" }
+                    }
+                };
+            }
 
             AddToolsToPayload(payload, toolOpts with { Iteration = iterations });
 
diff --git a/Services/AnthropicService.Streaming.cs b/Services/AnthropicService.Streaming.cs
index 0ae42ec..0a2a482 100644
--- a/Services/AnthropicService.Streaming.cs
+++ b/Services/AnthropicService.Streaming.cs
@@ -93,13 +93,17 @@ public partial class AnthropicService
                 {
                     ["model"] = modelId,
                     ["max_tokens"] = 16384,
-                    ["cache_control"] = new { type = "ephemeral" },
                     ["messages"] = messages,
                     ["stream"] = true
                 };
 
                 if (systemPrompt != null && systemPrompt.Count > 0)
+                {
+                    // Cache-Breakpoint auf den letzten System-Prompt-Block (1h TTL).
+                    // Idempotent über Iterationen.
+                    ApplyCacheControlToLast(systemPrompt);
                     payload["system"] = systemPrompt;
+                }
 
                 var remoteConn = remoteMgr?.GetBySessionId(sessionId);
                 var hasRemote = remoteConn != null;
diff --git a/Services/AnthropicService.cs b/Services/AnthropicService.cs
index 32e0ab7..b7ee941 100644
--- a/Services/AnthropicService.cs
+++ b/Services/AnthropicService.cs
@@ -318,6 +318,31 @@ public partial class AnthropicService
     private Task FinalizeChain(ChainRecord chain, TokenUsage usage, int iterations, string stopReason, System.Diagnostics.Stopwatch sw, string streamErrorInfo = null)
         => SseHelper.FinalizeChain(_db, chain, usage, iterations, stopReason, sw, streamErrorInfo);
 
+    /// <summary>
+    /// Versieht das letzte Element einer Block-Liste (Tools, System-Prompt-Blöcke, etc.) mit
+    /// einer cache_control-Annotation. Konvertiert das Element über JSON-Roundtrip in ein
+    /// Dictionary, damit cache_control auch bei anonymous types gesetzt werden kann.
+    /// Idempotent: Mehrfaches Aufrufen überschreibt nur das cache_control-Feld.
+    /// </summary>
+    private static void ApplyCacheControlToLast(List<object> blocks, string ttl = "1h")
+    {
+        if (blocks == null || blocks.Count == 0) return;
+        var last = blocks[blocks.Count - 1];
+        Dictionary<string, object> dict;
+        if (last is Dictionary<string, object> existing)
+        {
+            dict = existing;
+        }
+        else
+        {
+            var json = JsonSerializer.Serialize(last);
+            var parsed = JsonSerializer.Deserialize<Dictionary<string, object>>(json);
+            dict = parsed ?? new Dictionary<string, object>();
+        }
+        dict["cache_control"] = new { type = "ephemeral", ttl };
+        blocks[blocks.Count - 1] = dict;
+    }
+
     /// <summary>
     /// Fügt Tool-Definitionen und WebSearch zum Payload hinzu.
     /// </summary>
@@ -351,6 +376,10 @@ public partial class AnthropicService
             tools.Add(new { type = opts.WebSearchVersion, name = "web_search", max_uses = 5 });
             // web_search_20260209: Code Execution wird von der API automatisch injected – NICHT manuell hinzufügen!
         }
+        // Cache-Breakpoint auf das letzte Tool → cached den gesamten Tool-Block (1h TTL).
+        // Da Tools pro Iteration neu generiert werden, ist das idempotent.
+        ApplyCacheControlToLast(tools);
+
         payload["tools"] = tools;
         var effectiveChoice = (!opts.PlanMode && opts.ToolChoice == "any" && opts.Iteration == 1) ? "any" : "auto";
         payload["tool_choice"] = new { type = effectiveChoice };
@@ -405,7 +434,7 @@ public partial class AnthropicService
         var client = _httpFactory.CreateClient();
         client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", apiToken);
         client.DefaultRequestHeaders.Add("anthropic-version", "2023-06-01");
-        client.DefaultRequestHeaders.Add("anthropic-beta", "claude-code-20250219,oauth-2025-04-20,code-execution-2025-08-25");
+        client.DefaultRequestHeaders.Add("anthropic-beta", "claude-code-20250219,oauth-2025-04-20,code-execution-2025-08-25,extended-cache-ttl-2025-04-11");
         client.DefaultRequestHeaders.Add("User-Agent", "claude-cli/2.1.2 (external, cli)");
         client.DefaultRequestHeaders.Add("x-app", "cli");
         client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
diff --git a/Services/ClaudeCliService.cs b/Services/ClaudeCliService.cs
index 0a356f0..411a29f 100644
--- a/Services/ClaudeCliService.cs
+++ b/Services/ClaudeCliService.cs
@@ -70,6 +70,11 @@ public class ClaudeCliService
             StandardErrorEncoding = Encoding.UTF8
         };
 
+        // 1h-Prompt-Cache-TTL für Claude CLI aktivieren (seit CLI 2.1.108).
+        // Anthropic hat Anfang März 2026 den Default von 1h auf 5min gesenkt,
+        // dieser Flag holt die 1h-TTL zurück (gilt für API-Key, Bedrock, Vertex, Foundry).
+        psi.Environment["ENABLE_PROMPT_CACHING_1H"] = "1";
+
         foreach (var arg in args)
             psi.ArgumentList.Add(arg);