diff --git a/src/agents/cli-backends.ts b/src/agents/cli-backends.ts
index 1efc3b0c4..e32d112cb 100644
--- a/src/agents/cli-backends.ts
+++ b/src/agents/cli-backends.ts
@@ -44,9 +44,9 @@ const DEFAULT_CLAUDE_BACKEND: CliBackendConfig = {
   sessionArg: "--session-id",
   sessionMode: "always",
   sessionIdFields: ["session_id", "sessionId", "conversation_id", "conversationId"],
-  systemPromptArg: "--append-system-prompt",
+  systemPromptArg: "--system-prompt",
   systemPromptMode: "append",
-  systemPromptWhen: "first",
+  systemPromptWhen: "always",
   clearEnv: ["ANTHROPIC_API_KEY", "ANTHROPIC_API_KEY_OLD"],
   serialize: true,
   usageFields: {
diff --git a/src/agents/cli-runner/helpers.ts b/src/agents/cli-runner/helpers.ts
index 50891959b..f245e5b3a 100644
--- a/src/agents/cli-runner/helpers.ts
+++ b/src/agents/cli-runner/helpers.ts
@@ -438,7 +438,7 @@ export function buildCliArgs(params: {
   if (!params.useResume && params.backend.modelArg && params.modelId) {
     args.push(params.backend.modelArg, params.modelId);
   }
-  if (!params.useResume && params.systemPrompt && params.backend.systemPromptArg) {
+  if (params.systemPrompt && params.backend.systemPromptArg) {
     args.push(params.backend.systemPromptArg, params.systemPrompt);
   }
   if (!params.useResume && params.sessionId) {