diff --git a/apps/aether-gateway/src/ai_serving/planner/passthrough/provider/family/request.rs b/apps/aether-gateway/src/ai_serving/planner/passthrough/provider/family/request.rs
index 28f701b58..4bd50da98 100644
--- a/apps/aether-gateway/src/ai_serving/planner/passthrough/provider/family/request.rs
+++ b/apps/aether-gateway/src/ai_serving/planner/passthrough/provider/family/request.rs
@@ -316,7 +316,7 @@ pub(crate) async fn resolve_local_same_format_provider_candidate_payload_parts(
 
     // Same-format requests skip `apply_transport_request_body_semantics`, so the opt-in
     // Claude Code body mimicry has to be applied here as well.
-    if crate::provider_transport::claude_code::apply_claude_code_body_mimicry_for_transport(
+    if crate::ai_serving::transport::claude_code::apply_claude_code_body_mimicry_for_transport(
         &mut base_provider_request_body,
         &transport,
         prepared.provider_api_format.as_str(),
diff --git a/apps/aether-gateway/src/ai_serving/planner/standard/openai/chat/decision/request.rs b/apps/aether-gateway/src/ai_serving/planner/standard/openai/chat/decision/request.rs
index ce719f126..87d17fd6d 100644
--- a/apps/aether-gateway/src/ai_serving/planner/standard/openai/chat/decision/request.rs
+++ b/apps/aether-gateway/src/ai_serving/planner/standard/openai/chat/decision/request.rs
@@ -140,7 +140,7 @@ fn finalize_openai_chat_provider_request_body(
         mapped_model,
         source_model,
     );
-    crate::ai_serving::finalize_openai_provider_request_with_codex_model_capabilities_and_reasoning_replay_policy(
+    let finalization_failure = crate::ai_serving::finalize_openai_provider_request_with_codex_model_capabilities_and_reasoning_replay_policy(
         provider_request_body,
         crate::ai_serving::OpenAiProviderRequestFinalization {
             source_api_format: "openai:chat",
@@ -170,7 +170,17 @@ fn finalize_openai_chat_provider_request_body(
             provider_api_format,
             "openai_chat_request_finalization",
         )
-    })
+    });
+    if finalization_failure.is_none() {
+        // This builder does not go through `apply_transport_request_body_semantics`, so the
+        // Claude Code body mimicry must be applied here for Chat -> claude_code requests.
+        crate::ai_serving::transport::claude_code::apply_claude_code_body_mimicry_for_transport(
+            provider_request_body,
+            transport,
+            provider_api_format,
+        );
+    }
+    finalization_failure
 }
 
 #[allow(clippy::too_many_arguments)]
diff --git a/apps/aether-gateway/src/ai_serving/planner/standard/openai/responses/decision/request.rs b/apps/aether-gateway/src/ai_serving/planner/standard/openai/responses/decision/request.rs
index a9170ce59..0a52493bc 100644
--- a/apps/aether-gateway/src/ai_serving/planner/standard/openai/responses/decision/request.rs
+++ b/apps/aether-gateway/src/ai_serving/planner/standard/openai/responses/decision/request.rs
@@ -635,6 +635,13 @@ pub(crate) async fn resolve_local_openai_responses_candidate_payload_parts_with_
     {
         log_responses_to_chat_tool_conversion(trace_id, body_json, &base_provider_request_body);
     }
+    // This builder does not go through `apply_transport_request_body_semantics`, so the
+    // Claude Code body mimicry must be applied here for Responses -> claude_code requests.
+    crate::ai_serving::transport::claude_code::apply_claude_code_body_mimicry_for_transport(
+        &mut base_provider_request_body,
+        &transport,
+        provider_api_format,
+    );
     let provider_request_body = base_provider_request_body;
 
     if let Some(kiro_auth) = kiro_auth.as_ref() {
diff --git a/apps/aether-gateway/src/tests/ai_execute/sync/chat/local_decision.rs b/apps/aether-gateway/src/tests/ai_execute/sync/chat/local_decision.rs
index 9d97ebd83..71465d9f3 100644
--- a/apps/aether-gateway/src/tests/ai_execute/sync/chat/local_decision.rs
+++ b/apps/aether-gateway/src/tests/ai_execute/sync/chat/local_decision.rs
@@ -2028,14 +2028,30 @@ async fn gateway_returns_openai_chat_error_for_local_cross_format_claude_cli_syn
         "claude-code-upstream"
     );
     assert_eq!(seen_execution_runtime_request.body["max_tokens"], 64);
+    // claude_code providers get the Claude Code body shape: billing header + identity +
+    // generic prompt, with the client's own system moved into the message history.
+    let system = seen_execution_runtime_request.body["system"]
+        .as_array()
+        .expect("claude_code system should be rewritten into blocks");
+    assert_eq!(system.len(), 3);
+    assert!(system[0]["text"]
+        .as_str()
+        .is_some_and(|text| text.starts_with("x-anthropic-billing-header: cc_version=")));
     assert_eq!(
-        seen_execution_runtime_request.body["system"],
-        "You are terse."
+        system[1]["text"],
+        "You are Claude Code, Anthropic's official CLI for Claude."
     );
     assert_eq!(
         seen_execution_runtime_request.body["messages"],
-        json!([{"role":"user","content":"Say hello"}])
+        json!([
+            {"role":"user","content":[{"type":"text","text":"[System Instructions]\nYou are terse."}]},
+            {"role":"assistant","content":[{"type":"text","text":"Understood. I will follow these instructions."}]},
+            {"role":"user","content":"Say hello"}
+        ])
     );
+    assert!(seen_execution_runtime_request.body["metadata"]["user_id"]
+        .as_str()
+        .is_some_and(|user_id| user_id.contains("\"session_id\"")));
     assert_eq!(
         seen_execution_runtime_request.client_api_format,
         "openai:chat"