diff --git a/crates/protos/src/lib.rs b/crates/protos/src/lib.rs
index 8a9a39adc..d33594bc0 100644
--- a/crates/protos/src/lib.rs
+++ b/crates/protos/src/lib.rs
@@ -2442,7 +2442,7 @@ mod tests {
                 json_field: "batch_read_version_resps",
                 bin_field: "batch_read_version_resps_bin",
             },
-            json_encoder: "compat_response_json(batch_read_version_resp)",
+            json_encoder: "compat_response_json(batch_read_version_resp, false)",
         },
         ResponseCompatSendSite {
             field: CompatPayloadField {
@@ -2450,7 +2450,7 @@ mod tests {
                 json_field: "read_multiple_resps",
                 bin_field: "read_multiple_resps_bin",
             },
-            json_encoder: "compat_response_json(read_multiple_resp)",
+            json_encoder: "compat_response_json(read_multiple_resp, false)",
         },
         ResponseCompatSendSite {
             field: CompatPayloadField {
@@ -2458,7 +2458,7 @@ mod tests {
                 json_field: "file_info",
                 bin_field: "file_info_bin",
             },
-            json_encoder: "let file_info_json = compat_response_json(&file_info);",
+            json_encoder: "let file_info_json = compat_response_json(&file_info, request_had_msgpack_payload);",
         },
         ResponseCompatSendSite {
             field: CompatPayloadField {
@@ -2466,7 +2466,7 @@ mod tests {
                 json_field: "raw_file_info",
                 bin_field: "raw_file_info_bin",
             },
-            json_encoder: "let raw_file_info_json = compat_response_json(&raw_file_info);",
+            json_encoder: "let raw_file_info_json = compat_response_json(&raw_file_info, false);",
         },
         ResponseCompatSendSite {
             field: CompatPayloadField {
@@ -2474,7 +2474,7 @@ mod tests {
                 json_field: "rename_data_resp",
                 bin_field: "rename_data_resp_bin",
             },
-            json_encoder: "let rename_data_resp_json = compat_response_json(&rename_data_resp);",
+            json_encoder: "let rename_data_resp_json = compat_response_json(&rename_data_resp, false);",
         },
     ];
 
diff --git a/rustfs/src/storage/rpc/node_service/disk.rs b/rustfs/src/storage/rpc/node_service/disk.rs
index 75a16a45f..53588468e 100644
--- a/rustfs/src/storage/rpc/node_service/disk.rs
+++ b/rustfs/src/storage/rpc/node_service/disk.rs
@@ -141,11 +141,16 @@ fn verify_disk_mutation_digest<T>(
         .map_err(|err| Status::permission_denied(format!("{op} authentication failed: {err}")))
 }
 
-/// JSON compatibility string for a dual-encoded response field. Returns an empty string only when
-/// msgpack-only mode and its explicit fleet confirmation guard are both enabled; otherwise the
-/// legacy JSON encoding is retained for old peers. The paired `_bin` field is always sent.
-fn compat_response_json<T: serde::Serialize>(value: &T) -> std::result::Result<String, serde_json::Error> {
-    if rustfs_protos::internode_rpc_msgpack_only() {
+/// JSON compatibility string for a dual-encoded response field. Returns an empty string when
+/// msgpack-only mode and its explicit fleet confirmation guard are both enabled, or when
+/// request-local `_bin` payloads prove the caller can consume the paired response `_bin` field,
+/// while legacy JSON-only callers still need the compatibility response string during rollout.
+/// The paired `_bin` field is always sent.
+fn compat_response_json<T: serde::Serialize>(
+    value: &T,
+    request_had_msgpack_payload: bool,
+) -> std::result::Result<String, serde_json::Error> {
+    if request_had_msgpack_payload || rustfs_protos::internode_rpc_msgpack_only() {
         return Ok(String::new());
     }
     serde_json::to_string(value)
@@ -159,7 +164,7 @@ fn encode_read_multiple_response_payloads(
 
     for read_multiple_resp in read_multiple_resps {
         read_multiple_resps_json.push(
-            compat_response_json(read_multiple_resp)
+            compat_response_json(read_multiple_resp, false)
                 .map_err(|err| DiskError::other(format!("encode ReadMultipleResp json failed: {err}")))?,
         );
         read_multiple_resps_bin.push(Bytes::from(encode_msgpack(read_multiple_resp, "ReadMultipleResp")?));
@@ -176,7 +181,7 @@ fn encode_batch_read_version_response_payloads(
 
     for batch_read_version_resp in batch_read_version_resps {
         batch_read_version_resps_json.push(
-            compat_response_json(batch_read_version_resp)
+            compat_response_json(batch_read_version_resp, false)
                 .map_err(|err| DiskError::other(format!("encode BatchReadVersionResp json failed: {err}")))?,
         );
         batch_read_version_resps_bin.push(Bytes::from(encode_msgpack_with_capacity(
@@ -571,7 +576,7 @@ impl NodeService {
         if let Some(disk) = self.find_disk(&request.disk).await {
             match disk.read_xl(&request.volume, &request.path, request.read_data).await {
                 Ok(raw_file_info) => {
-                    let raw_file_info_json = compat_response_json(&raw_file_info);
+                    let raw_file_info_json = compat_response_json(&raw_file_info, false);
                     let raw_file_info_bin = encode_msgpack(&raw_file_info, "RawFileInfo");
                     match (raw_file_info_json, raw_file_info_bin) {
                         (Ok(raw_file_info), Ok(raw_file_info_bin)) => Ok(Response::new(ReadXlResponse {
@@ -617,6 +622,7 @@ impl NodeService {
     ) -> Result<Response<ReadVersionResponse>, Status> {
         let request = request.into_inner();
         if let Some(disk) = self.find_disk(&request.disk).await {
+            let request_had_msgpack_payload = !request.opts_bin.is_empty();
             let opts = match decode_msgpack_or_json::<ReadOptions>(&request.opts_bin, &request.opts, "ReadOptions") {
                 Ok(options) => options,
                 Err(err) => {
@@ -633,7 +639,7 @@ impl NodeService {
                 .await
             {
                 Ok(file_info) => {
-                    let file_info_json = compat_response_json(&file_info);
+                    let file_info_json = compat_response_json(&file_info, request_had_msgpack_payload);
                     let file_info_bin = encode_file_info_msgpack(&file_info);
                     match (file_info_json, file_info_bin) {
                         (Ok(file_info), Ok(file_info_bin)) => Ok(Response::new(ReadVersionResponse {
@@ -979,7 +985,7 @@ impl NodeService {
                 .await
             {
                 Ok(rename_data_resp) => {
-                    let rename_data_resp_json = compat_response_json(&rename_data_resp);
+                    let rename_data_resp_json = compat_response_json(&rename_data_resp, false);
                     let rename_data_resp_bin = encode_msgpack_named(&rename_data_resp, "RenameDataResp");
                     match (rename_data_resp_json, rename_data_resp_bin) {
                         (Ok(rename_data_resp), Ok(rename_data_resp_bin)) => Ok(Response::new(RenameDataResponse {
@@ -1527,7 +1533,7 @@ mod tests {
                     name: "legacy-json".to_string(),
                     count: 9,
                 };
-                let json = compat_response_json(&payload).expect("compat response json should encode");
+                let json = compat_response_json(&payload, false).expect("compat response json should encode");
 
                 assert!(!json.is_empty(), "old JSON clients must remain compatible without fleet confirmation");
                 assert_eq!(json, serde_json::to_string(&payload).expect("json should encode"));
@@ -1547,7 +1553,7 @@ mod tests {
                     name: "msgpack-only".to_string(),
                     count: 10,
                 };
-                let json = compat_response_json(&payload).expect("compat response json should encode");
+                let json = compat_response_json(&payload, false).expect("compat response json should encode");
 
                 assert!(json.is_empty(), "msgpack-only may empty JSON only after explicit fleet confirmation");
             },
@@ -1567,7 +1573,7 @@ mod tests {
                 (rustfs_config::ENV_INTERNODE_RPC_MSGPACK_ONLY_FLEET_CONFIRMED, Some("true")),
             ],
             || {
-                let json = compat_response_json(&payload).expect("compat response json should encode");
+                let json = compat_response_json(&payload, false).expect("compat response json should encode");
 
                 assert!(json.is_empty(), "both gates should enter msgpack-only response mode");
             },
@@ -1584,7 +1590,7 @@ mod tests {
             ],
         ] {
             with_internode_msgpack_env(vars, || {
-                let json = compat_response_json(&payload).expect("compat response json should encode");
+                let json = compat_response_json(&payload, false).expect("compat response json should encode");
 
                 assert!(!json.is_empty(), "removing either gate should restore old-peer JSON compatibility");
                 assert_eq!(json, serde_json::to_string(&payload).expect("json should encode"));
@@ -1592,6 +1598,45 @@ mod tests {
         }
     }
 
+    #[test]
+    fn compat_response_json_omits_json_for_msgpack_capable_request_without_fleet_gate() {
+        with_internode_msgpack_env(
+            [
+                (rustfs_config::ENV_INTERNODE_RPC_MSGPACK_ONLY, None::<&str>),
+                (rustfs_config::ENV_INTERNODE_RPC_MSGPACK_ONLY_FLEET_CONFIRMED, None::<&str>),
+            ],
+            || {
+                let payload = SamplePayload {
+                    name: "request-local-bin".to_string(),
+                    count: 13,
+                };
+                let json = compat_response_json(&payload, true).expect("compat response json should encode");
+
+                assert!(json.is_empty(), "a request-local msgpack payload may receive a bin-only response");
+            },
+        );
+    }
+
+    #[test]
+    fn compat_response_json_keeps_json_for_legacy_json_request() {
+        with_internode_msgpack_env(
+            [
+                (rustfs_config::ENV_INTERNODE_RPC_MSGPACK_ONLY, None::<&str>),
+                (rustfs_config::ENV_INTERNODE_RPC_MSGPACK_ONLY_FLEET_CONFIRMED, None::<&str>),
+            ],
+            || {
+                let payload = SamplePayload {
+                    name: "legacy-request-json".to_string(),
+                    count: 14,
+                };
+                let json = compat_response_json(&payload, false).expect("compat response json should encode");
+
+                assert!(!json.is_empty(), "legacy JSON-only callers must keep receiving response JSON");
+                assert_eq!(json, serde_json::to_string(&payload).expect("json should encode"));
+            },
+        );
+    }
+
     #[test]
     fn decode_msgpack_or_json_fails_closed_on_corrupt_non_empty_msgpack() {
         let before = global_internode_metrics().msgpack_json_decode_error_total_for_test();