diff --git a/.changesets/maint_bnjjj_fix_3929.md b/.changesets/maint_bnjjj_fix_3929.md
new file mode 100644
index 0000000000..a4e1d82df6
--- /dev/null
+++ b/.changesets/maint_bnjjj_fix_3929.md
@@ -0,0 +1,5 @@
+### Router should respond with subscription-protocol header for callback ([Issue #3929](https://github.com/apollographql/router/issues/3929))
+
+Callback protocol documentation specifies that router responds with `subscription-protocol: callback/1.0` header to the initialization (check) message. Currently router does not set this header on the response.
+
+By [@bnjjj](https://github.com/bnjjj) in https://github.com/apollographql/router/pull/3939
\ No newline at end of file
diff --git a/apollo-router/src/plugins/subscription.rs b/apollo-router/src/plugins/subscription.rs
index ee8023c368..0aa2c1765e 100644
--- a/apollo-router/src/plugins/subscription.rs
+++ b/apollo-router/src/plugins/subscription.rs
@@ -7,6 +7,8 @@ use bytes::Buf;
 use futures::future::BoxFuture;
 use hmac::Hmac;
 use hmac::Mac;
+use http::HeaderName;
+use http::HeaderValue;
 use http::Method;
 use http::StatusCode;
 use multimap::MultiMap;
@@ -46,6 +48,8 @@ pub(crate) const APOLLO_SUBSCRIPTION_PLUGIN_NAME: &str = "subscription";
 pub(crate) static SUBSCRIPTION_CALLBACK_HMAC_KEY: OnceCell<String> = OnceCell::new();
 pub(crate) const SUBSCRIPTION_WS_CUSTOM_CONNECTION_PARAMS: &str =
     "apollo.subscription.custom_connection_params";
+const CALLBACK_SUBSCRIPTION_HEADER_NAME: &str = "subscription-protocol";
+const CALLBACK_SUBSCRIPTION_HEADER_VALUE: &str = "callback/1.0";
 
 #[derive(Debug, Clone)]
 pub(crate) struct Subscription {
@@ -464,6 +468,7 @@ impl Service<router::Request> for CallbackService {
                                     Ok(router::Response {
                                         response: http::Response::builder()
                                             .status(StatusCode::NO_CONTENT)
+                                            .header(HeaderName::from_static(CALLBACK_SUBSCRIPTION_HEADER_NAME), HeaderValue::from_static(CALLBACK_SUBSCRIPTION_HEADER_VALUE))
                                             .body::<hyper::Body>("".into())
                                             .map_err(BoxError::from)?,
                                         context: req.context,
@@ -472,6 +477,7 @@ impl Service<router::Request> for CallbackService {
                                     Ok(router::Response {
                                         response: http::Response::builder()
                                             .status(StatusCode::NOT_FOUND)
+                                            .header(HeaderName::from_static(CALLBACK_SUBSCRIPTION_HEADER_NAME), HeaderValue::from_static(CALLBACK_SUBSCRIPTION_HEADER_VALUE))
                                             .body("suscription doesn't exist".into())
                                             .map_err(BoxError::from)?,
                                         context: req.context,
@@ -694,6 +700,12 @@ mod tests {
         .unwrap();
         let resp = web_endpoint.clone().oneshot(http_req).await.unwrap();
         assert_eq!(resp.status(), http::StatusCode::NO_CONTENT);
+        assert_eq!(
+            resp.headers()
+                .get(HeaderName::from_static(CALLBACK_SUBSCRIPTION_HEADER_NAME))
+                .unwrap(),
+            HeaderValue::from_static(CALLBACK_SUBSCRIPTION_HEADER_VALUE)
+        );
 
         let http_req = http::Request::post(format!(
             "http://localhost:4000/subscription/callback/{new_sub_id}"
@@ -912,6 +924,12 @@ mod tests {
         .unwrap();
         let resp = web_endpoint.clone().oneshot(http_req).await.unwrap();
         assert_eq!(resp.status(), http::StatusCode::NO_CONTENT);
+        assert_eq!(
+            resp.headers()
+                .get(HeaderName::from_static(CALLBACK_SUBSCRIPTION_HEADER_NAME))
+                .unwrap(),
+            HeaderValue::from_static(CALLBACK_SUBSCRIPTION_HEADER_VALUE)
+        );
 
         let http_req = http::Request::post(format!(
             "http://localhost:4000/subscription/callback/{new_sub_id}"