diff --git a/tools/server/server-task.cpp b/tools/server/server-task.cpp
index 3f30da2cd..2e513a33e 100644
--- a/tools/server/server-task.cpp
+++ b/tools/server/server-task.cpp
@@ -591,8 +591,10 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp() {
 json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
     std::vector<json> server_sent_events;
     std::vector<json> output;
+    size_t output_index = 0;
 
     if (oaicompat_msg.reasoning_content != "") {
+        const size_t item_output_index = output_index++;
         const json output_item = json {
             {"id",      oai_resp_reasoning_id},
             {"summary", json::array()},
@@ -608,6 +610,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
             {"event", "response.output_item.done"},
             {"data", json {
                 {"type", "response.output_item.done"},
+                {"output_index", item_output_index},
                 {"item", output_item}
             }}
         });
@@ -615,11 +618,14 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
     }
 
     if (oaicompat_msg.content != "") {
+        const size_t item_output_index = output_index++;
         server_sent_events.push_back(json {
             {"event", "response.output_text.done"},
             {"data", json {
                 {"type",    "response.output_text.done"},
                 {"item_id", oai_resp_message_id},
+                {"output_index", item_output_index},
+                {"content_index", 0},
                 {"text",    oaicompat_msg.content}
             }}
         });
@@ -636,6 +642,8 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
             {"data", json {
                 {"type",    "response.content_part.done"},
                 {"item_id", oai_resp_message_id},
+                {"output_index", item_output_index},
+                {"content_index", 0},
                 {"part",    content_part}
             }}
         });
@@ -651,6 +659,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
             {"event", "response.output_item.done"},
             {"data", json {
                 {"type", "response.output_item.done"},
+                {"output_index", item_output_index},
                 {"item", output_item}
             }}
         });
@@ -658,6 +667,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
     }
 
     for (const common_chat_tool_call & tool_call : oaicompat_msg.tool_calls) {
+        const size_t item_output_index = output_index++;
         const json output_item = {
             {"id",        "fc_" + tool_call.id},
             {"type",      "function_call"},
@@ -670,6 +680,7 @@ json server_task_result_cmpl_final::to_json_oaicompat_resp_stream() {
             {"event", "response.output_item.done"},
             {"data", json {
                 {"type", "response.output_item.done"},
+                {"output_index", item_output_index},
                 {"item", output_item}
             }}
         });
@@ -1202,6 +1213,7 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                     {"event", "response.output_item.added"},
                     {"data", json {
                         {"type", "response.output_item.added"},
+                        {"output_index", 0},
                         {"item", json {
                             {"id",                oai_resp_reasoning_id},
                             {"summary",           json::array()},
@@ -1218,6 +1230,8 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                 {"event", "response.reasoning_text.delta"},
                 {"data", json {
                     {"type",    "response.reasoning_text.delta"},
+                    {"output_index", 0},
+                    {"content_index", 0},
                     {"delta",   diff.reasoning_content_delta},
                     {"item_id", oai_resp_reasoning_id},
                 }},
@@ -1230,6 +1244,7 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                     {"event", "response.output_item.added"},
                     {"data", json {
                         {"type", "response.output_item.added"},
+                        {"output_index", anthropic_has_reasoning ? 1 : 0},
                         {"item", json {
                             {"content", json::array()},
                             {"id",      oai_resp_message_id},
@@ -1244,6 +1259,8 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                     {"data", json {
                         {"type",    "response.content_part.added"},
                         {"item_id", oai_resp_message_id},
+                        {"output_index", anthropic_has_reasoning ? 1 : 0},
+                        {"content_index", 0},
                         {"part", json {
                             {"type", "output_text"},
                             {"text", ""},
@@ -1257,6 +1274,8 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                 {"data", json {
                     {"type",    "response.output_text.delta"},
                     {"item_id", oai_resp_message_id},
+                    {"output_index", anthropic_has_reasoning ? 1 : 0},
+                    {"content_index", 0},
                     {"delta",   diff.content_delta},
                 }},
             });
@@ -1267,6 +1286,7 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                 {"event", "response.output_item.added"},
                 {"data", json {
                     {"type",  "response.output_item.added"},
+                    {"output_index", (anthropic_has_reasoning ? 1 : 0) + (text_block_started ? 1 : 0) + diff.tool_call_index},
                     {"item", json {
                         {"id",        "fc_" + diff.tool_call_delta.id},
                         {"arguments", ""},
@@ -1287,6 +1307,7 @@ json server_task_result_cmpl_partial::to_json_oaicompat_resp() {
                     {"type",    "response.function_call_arguments.delta"},
                     {"delta",   diff.tool_call_delta.arguments},
                     {"item_id", "fc_" + oai_resp_fc_id},
+                    {"output_index", (anthropic_has_reasoning ? 1 : 0) + (text_block_started ? 1 : 0) + diff.tool_call_index},
                 }},
             });
         }