diff --git a/protocols/autonat/src/v2/client/handler/dial_back.rs b/protocols/autonat/src/v2/client/handler/dial_back.rs
index ef544a4c77a..7cdf194343a 100644
--- a/protocols/autonat/src/v2/client/handler/dial_back.rs
+++ b/protocols/autonat/src/v2/client/handler/dial_back.rs
@@ -35,16 +35,14 @@ impl ConnectionHandler for Handler {
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(ReadyUpgrade::new(DIAL_BACK_PROTOCOL), ())
     }
 
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         loop {
             match self.inbound.poll_next_unpin(cx) {
                 Poll::Pending => return Poll::Pending,
@@ -68,12 +66,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/protocols/autonat/src/v2/client/handler/dial_request.rs b/protocols/autonat/src/v2/client/handler/dial_request.rs
index fff83ad9453..61f564505eb 100644
--- a/protocols/autonat/src/v2/client/handler/dial_request.rs
+++ b/protocols/autonat/src/v2/client/handler/dial_request.rs
@@ -72,7 +72,7 @@ pub struct Handler {
     queued_events: VecDeque<
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::ToBehaviour,
         >,
     >,
@@ -121,16 +121,14 @@ impl ConnectionHandler for Handler {
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         if let Some(event) = self.queued_events.pop_front() {
             return Poll::Ready(event);
         }
@@ -161,12 +159,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::DialUpgradeError(DialUpgradeError { error, .. }) => {
diff --git a/protocols/autonat/src/v2/server/handler/dial_back.rs b/protocols/autonat/src/v2/server/handler/dial_back.rs
index 61593da318d..8adb33509ef 100644
--- a/protocols/autonat/src/v2/server/handler/dial_back.rs
+++ b/protocols/autonat/src/v2/server/handler/dial_back.rs
@@ -46,16 +46,14 @@ impl ConnectionHandler for Handler {
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         if let Poll::Ready(result) = self.outbound.poll_unpin(cx) {
             return Poll::Ready(ConnectionHandlerEvent::NotifyBehaviour(
                 result
@@ -76,12 +74,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedOutbound(FullyNegotiatedOutbound {
diff --git a/protocols/autonat/src/v2/server/handler/dial_request.rs b/protocols/autonat/src/v2/server/handler/dial_request.rs
index 5058e0f3f42..22cab2b9cab 100644
--- a/protocols/autonat/src/v2/server/handler/dial_request.rs
+++ b/protocols/autonat/src/v2/server/handler/dial_request.rs
@@ -81,16 +81,14 @@ where
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(ReadyUpgrade::new(DIAL_REQUEST_PROTOCOL), ())
     }
 
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         loop {
             match self.inbound.poll_unpin(cx) {
                 Poll::Ready(Ok(event)) => {
@@ -117,12 +115,7 @@ where
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/protocols/dcutr/src/handler/relayed.rs b/protocols/dcutr/src/handler/relayed.rs
index 0d6e1b5e889..47813493e9e 100644
--- a/protocols/dcutr/src/handler/relayed.rs
+++ b/protocols/dcutr/src/handler/relayed.rs
@@ -65,7 +65,7 @@ pub struct Handler {
     queued_events: VecDeque<
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::ToBehaviour,
         >,
     >,
@@ -98,10 +98,7 @@ impl Handler {
         &mut self,
         FullyNegotiatedInbound {
             protocol: output, ..
-        }: FullyNegotiatedInbound<
-            <Self as ConnectionHandler>::InboundProtocol,
-            <Self as ConnectionHandler>::InboundOpenInfo,
-        >,
+        }: FullyNegotiatedInbound<<Self as ConnectionHandler>::InboundProtocol>,
     ) {
         match output {
             future::Either::Left(stream) => {
@@ -130,10 +127,7 @@ impl Handler {
         &mut self,
         FullyNegotiatedOutbound {
             protocol: stream, ..
-        }: FullyNegotiatedOutbound<
-            <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
-        >,
+        }: FullyNegotiatedOutbound<<Self as ConnectionHandler>::OutboundProtocol>,
     ) {
         assert!(
             self.endpoint.is_listener(),
@@ -156,7 +150,7 @@ impl Handler {
     fn on_listen_upgrade_error(
         &mut self,
         ListenUpgradeError { error, .. }: ListenUpgradeError<
-            <Self as ConnectionHandler>::InboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::InboundProtocol,
         >,
     ) {
@@ -168,7 +162,7 @@ impl Handler {
     fn on_dial_upgrade_error(
         &mut self,
         DialUpgradeError { error, .. }: DialUpgradeError<
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::OutboundProtocol,
         >,
     ) {
@@ -196,7 +190,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         match self.endpoint {
             ConnectedPoint::Dialer { .. } => {
                 SubstreamProtocol::new(Either::Left(ReadyUpgrade::new(PROTOCOL_NAME)), ())
@@ -236,9 +230,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         // Return queued events.
         if let Some(event) = self.queued_events.pop_front() {
             return Poll::Ready(event);
@@ -295,12 +287,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(fully_negotiated_inbound) => {
diff --git a/protocols/gossipsub/src/handler.rs b/protocols/gossipsub/src/handler.rs
index e66b606896b..f93e993a854 100644
--- a/protocols/gossipsub/src/handler.rs
+++ b/protocols/gossipsub/src/handler.rs
@@ -198,7 +198,6 @@ impl EnabledHandler {
         &mut self,
         FullyNegotiatedOutbound { protocol, .. }: FullyNegotiatedOutbound<
             <Handler as ConnectionHandler>::OutboundProtocol,
-            <Handler as ConnectionHandler>::OutboundOpenInfo,
         >,
     ) {
         let (substream, peer_kind) = protocol;
@@ -221,7 +220,7 @@ impl EnabledHandler {
     ) -> Poll<
         ConnectionHandlerEvent<
             <Handler as ConnectionHandler>::OutboundProtocol,
-            <Handler as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Handler as ConnectionHandler>::ToBehaviour,
         >,
     > {
@@ -427,7 +426,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type OutboundProtocol = ProtocolConfig;
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         match self {
             Handler::Enabled(handler) => {
                 SubstreamProtocol::new(either::Either::Left(handler.listen_protocol.clone()), ())
@@ -462,9 +461,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         match self {
             Handler::Enabled(handler) => handler.poll(cx),
             Handler::Disabled(DisabledHandler::ProtocolUnsupported { peer_kind_sent }) => {
@@ -483,12 +480,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match self {
             Handler::Enabled(handler) => {
diff --git a/protocols/identify/src/handler.rs b/protocols/identify/src/handler.rs
index 6e5af290cd2..7acdfceb0a6 100644
--- a/protocols/identify/src/handler.rs
+++ b/protocols/identify/src/handler.rs
@@ -159,10 +159,7 @@ impl Handler {
         &mut self,
         FullyNegotiatedInbound {
             protocol: output, ..
-        }: FullyNegotiatedInbound<
-            <Self as ConnectionHandler>::InboundProtocol,
-            <Self as ConnectionHandler>::InboundOpenInfo,
-        >,
+        }: FullyNegotiatedInbound<<Self as ConnectionHandler>::InboundProtocol>,
     ) {
         match output {
             future::Either::Left(stream) => {
@@ -198,10 +195,7 @@ impl Handler {
         &mut self,
         FullyNegotiatedOutbound {
             protocol: output, ..
-        }: FullyNegotiatedOutbound<
-            <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
-        >,
+        }: FullyNegotiatedOutbound<<Self as ConnectionHandler>::OutboundProtocol>,
     ) {
         match output {
             future::Either::Left(stream) => {
@@ -303,7 +297,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(
             SelectUpgrade::new(
                 ReadyUpgrade::new(PROTOCOL_NAME),
@@ -334,7 +328,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Event>> {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Event>> {
         if let Some(event) = self.events.pop() {
             return Poll::Ready(event);
         }
@@ -413,12 +407,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(fully_negotiated_inbound) => {
diff --git a/protocols/kad/src/handler.rs b/protocols/kad/src/handler.rs
index 6837e3d499e..b848cf94410 100644
--- a/protocols/kad/src/handler.rs
+++ b/protocols/kad/src/handler.rs
@@ -476,10 +476,7 @@ impl Handler {
         FullyNegotiatedOutbound {
             protocol: stream,
             info: (),
-        }: FullyNegotiatedOutbound<
-            <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
-        >,
+        }: FullyNegotiatedOutbound<<Self as ConnectionHandler>::OutboundProtocol>,
     ) {
         if let Some(sender) = self.pending_streams.pop_front() {
             let _ = sender.send(Ok(stream));
@@ -500,7 +497,6 @@ impl Handler {
         &mut self,
         FullyNegotiatedInbound { protocol, .. }: FullyNegotiatedInbound<
             <Self as ConnectionHandler>::InboundProtocol,
-            <Self as ConnectionHandler>::InboundOpenInfo,
         >,
     ) {
         // If `self.allow_listening` is false, then we produced a `DeniedUpgrade` and `protocol`
@@ -608,7 +604,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         match self.mode {
             Mode::Server => SubstreamProtocol::new(Either::Left(self.protocol_config.clone()), ()),
             Mode::Client => SubstreamProtocol::new(Either::Right(upgrade::DeniedUpgrade), ()),
@@ -719,9 +715,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         loop {
             match &mut self.protocol_status {
                 Some(status) if !status.reported => {
@@ -788,12 +782,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedOutbound(fully_negotiated_outbound) => {
diff --git a/protocols/perf/src/client/handler.rs b/protocols/perf/src/client/handler.rs
index fc427d8134c..043790822b5 100644
--- a/protocols/perf/src/client/handler.rs
+++ b/protocols/perf/src/client/handler.rs
@@ -58,7 +58,7 @@ pub struct Handler {
     queued_events: VecDeque<
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::ToBehaviour,
         >,
     >,
@@ -92,7 +92,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
@@ -106,12 +106,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             // TODO: remove when Rust 1.82 is MSRV
@@ -161,9 +156,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         if let Some(event) = self.queued_events.pop_front() {
             return Poll::Ready(event);
         }
diff --git a/protocols/perf/src/server/handler.rs b/protocols/perf/src/server/handler.rs
index a78485cd9b5..6ecb19dbc18 100644
--- a/protocols/perf/src/server/handler.rs
+++ b/protocols/perf/src/server/handler.rs
@@ -70,7 +70,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = Infallible;
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(ReadyUpgrade::new(crate::PROTOCOL_NAME), ())
     }
 
@@ -82,12 +82,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol, (), Infallible>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
@@ -129,9 +124,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, Infallible, Self::ToBehaviour>> {
         loop {
             match self.inbound.poll_unpin(cx) {
                 Poll::Ready(Ok(Ok(stats))) => {
diff --git a/protocols/ping/src/handler.rs b/protocols/ping/src/handler.rs
index c7d65c64500..510ff0553de 100644
--- a/protocols/ping/src/handler.rs
+++ b/protocols/ping/src/handler.rs
@@ -179,7 +179,7 @@ impl Handler {
     fn on_dial_upgrade_error(
         &mut self,
         DialUpgradeError { error, .. }: DialUpgradeError<
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::OutboundProtocol,
         >,
     ) {
@@ -229,7 +229,7 @@ impl ConnectionHandler for Handler {
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<ReadyUpgrade<StreamProtocol>, ()> {
+    fn listen_protocol(&self) -> SubstreamProtocol<ReadyUpgrade<StreamProtocol>> {
         SubstreamProtocol::new(ReadyUpgrade::new(PROTOCOL_NAME), ())
     }
 
@@ -340,12 +340,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/protocols/relay/src/behaviour/handler.rs b/protocols/relay/src/behaviour/handler.rs
index 0a4fe11c00a..d714bf04fc9 100644
--- a/protocols/relay/src/behaviour/handler.rs
+++ b/protocols/relay/src/behaviour/handler.rs
@@ -343,7 +343,7 @@ pub struct Handler {
     queued_events: VecDeque<
         ConnectionHandlerEvent<
             <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::ToBehaviour,
         >,
     >,
@@ -447,7 +447,7 @@ impl Handler {
     fn on_dial_upgrade_error(
         &mut self,
         DialUpgradeError { error, .. }: DialUpgradeError<
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::OutboundProtocol,
         >,
     ) {
@@ -494,7 +494,7 @@ impl ConnectionHandler for Handler {
     type OutboundProtocol = ReadyUpgrade<StreamProtocol>;
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(ReadyUpgrade::new(HOP_PROTOCOL_NAME), ())
     }
 
@@ -598,9 +598,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         // Return queued events.
         if let Some(event) = self.queued_events.pop_front() {
             return Poll::Ready(event);
@@ -876,12 +874,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/protocols/relay/src/priv_client/handler.rs b/protocols/relay/src/priv_client/handler.rs
index 8f60b689ec8..d2e4db56b4c 100644
--- a/protocols/relay/src/priv_client/handler.rs
+++ b/protocols/relay/src/priv_client/handler.rs
@@ -107,7 +107,7 @@ pub struct Handler {
     queued_events: VecDeque<
         ConnectionHandlerEvent<
             <Handler as ConnectionHandler>::OutboundProtocol,
-            <Handler as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Handler as ConnectionHandler>::ToBehaviour,
         >,
     >,
@@ -241,7 +241,7 @@ impl ConnectionHandler for Handler {
     type OutboundProtocol = ReadyUpgrade<StreamProtocol>;
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(ReadyUpgrade::new(STOP_PROTOCOL_NAME), ())
     }
 
@@ -267,9 +267,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         loop {
             // Reservations
             match self.inflight_reserve_requests.poll_unpin(cx) {
@@ -426,12 +424,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/protocols/request-response/src/handler.rs b/protocols/request-response/src/handler.rs
index 133cff87f40..d70ddc5c0ae 100644
--- a/protocols/request-response/src/handler.rs
+++ b/protocols/request-response/src/handler.rs
@@ -127,10 +127,7 @@ where
         FullyNegotiatedInbound {
             protocol: (mut stream, protocol),
             info: (),
-        }: FullyNegotiatedInbound<
-            <Self as ConnectionHandler>::InboundProtocol,
-            <Self as ConnectionHandler>::InboundOpenInfo,
-        >,
+        }: FullyNegotiatedInbound<<Self as ConnectionHandler>::InboundProtocol>,
     ) {
         let mut codec = self.codec.clone();
         let request_id = self.next_inbound_request_id();
@@ -178,10 +175,7 @@ where
         FullyNegotiatedOutbound {
             protocol: (mut stream, protocol),
             info: (),
-        }: FullyNegotiatedOutbound<
-            <Self as ConnectionHandler>::OutboundProtocol,
-            <Self as ConnectionHandler>::OutboundOpenInfo,
-        >,
+        }: FullyNegotiatedOutbound<<Self as ConnectionHandler>::OutboundProtocol>,
     ) {
         let message = self
             .requested_outbound
@@ -219,7 +213,7 @@ where
     fn on_dial_upgrade_error(
         &mut self,
         DialUpgradeError { error, info: () }: DialUpgradeError<
-            <Self as ConnectionHandler>::OutboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::OutboundProtocol,
         >,
     ) {
@@ -256,7 +250,7 @@ where
     fn on_listen_upgrade_error(
         &mut self,
         ListenUpgradeError { error, .. }: ListenUpgradeError<
-            <Self as ConnectionHandler>::InboundOpenInfo,
+            (),
             <Self as ConnectionHandler>::InboundProtocol,
         >,
     ) {
@@ -383,7 +377,7 @@ where
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(
             Protocol {
                 protocols: self.inbound_protocols.clone(),
@@ -473,12 +467,7 @@ where
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(fully_negotiated_inbound) => {
diff --git a/protocols/stream/src/handler.rs b/protocols/stream/src/handler.rs
index d626f48fb09..5fc903f5980 100644
--- a/protocols/stream/src/handler.rs
+++ b/protocols/stream/src/handler.rs
@@ -52,9 +52,7 @@ impl ConnectionHandler for Handler {
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(
-        &self,
-    ) -> swarm::SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> swarm::SubstreamProtocol<Self::InboundProtocol> {
         swarm::SubstreamProtocol::new(
             Upgrade {
                 supported_protocols: Shared::lock(&self.shared).supported_inbound_protocols(),
@@ -66,13 +64,7 @@ impl ConnectionHandler for Handler {
     fn poll(
         &mut self,
         cx: &mut Context<'_>,
-    ) -> Poll<
-        swarm::ConnectionHandlerEvent<
-            Self::OutboundProtocol,
-            Self::OutboundOpenInfo,
-            Self::ToBehaviour,
-        >,
-    > {
+    ) -> Poll<swarm::ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         if self.pending_upgrade.is_some() {
             return Poll::Pending;
         }
@@ -104,12 +96,7 @@ impl ConnectionHandler for Handler {
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/swarm/benches/connection_handler.rs b/swarm/benches/connection_handler.rs
index a5e47528308..3ae75288208 100644
--- a/swarm/benches/connection_handler.rs
+++ b/swarm/benches/connection_handler.rs
@@ -281,9 +281,7 @@ impl ConnectionHandler for SpinningHandler {
 
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(
-        &self,
-    ) -> libp2p_swarm::SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> libp2p_swarm::SubstreamProtocol<Self::InboundProtocol> {
         libp2p_swarm::SubstreamProtocol::new(Upgrade(self.protocols), ())
     }
 
@@ -291,11 +289,7 @@ impl ConnectionHandler for SpinningHandler {
         &mut self,
         cx: &mut std::task::Context<'_>,
     ) -> std::task::Poll<
-        libp2p_swarm::ConnectionHandlerEvent<
-            Self::OutboundProtocol,
-            Self::OutboundOpenInfo,
-            Self::ToBehaviour,
-        >,
+        libp2p_swarm::ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>,
     > {
         if self.iter_count == usize::MAX {
             return std::task::Poll::Pending;
@@ -322,8 +316,6 @@ impl ConnectionHandler for SpinningHandler {
         _event: libp2p_swarm::handler::ConnectionEvent<
             Self::InboundProtocol,
             Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
         >,
     ) {
     }
diff --git a/swarm/src/behaviour/toggle.rs b/swarm/src/behaviour/toggle.rs
index e70e6cf9896..a706187a40c 100644
--- a/swarm/src/behaviour/toggle.rs
+++ b/swarm/src/behaviour/toggle.rs
@@ -200,6 +200,7 @@ impl<TInner> ToggleConnectionHandler<TInner>
 where
     TInner: ConnectionHandler,
 {
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     fn on_fully_negotiated_inbound(
         &mut self,
         FullyNegotiatedInbound {
@@ -231,7 +232,7 @@ where
             panic!("Unexpected Either::Right in enabled `on_fully_negotiated_inbound`.")
         }
     }
-
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     fn on_listen_upgrade_error(
         &mut self,
         ListenUpgradeError { info, error: err }: ListenUpgradeError<
@@ -267,6 +268,7 @@ where
     }
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<TInner> ConnectionHandler for ToggleConnectionHandler<TInner>
 where
     TInner: ConnectionHandler,
diff --git a/swarm/src/connection.rs b/swarm/src/connection.rs
index a1c7b2a2f20..8e913aa80e5 100644
--- a/swarm/src/connection.rs
+++ b/swarm/src/connection.rs
@@ -123,6 +123,7 @@ where
     /// The underlying handler.
     handler: THandler,
     /// Futures that upgrade incoming substreams.
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     negotiating_in: FuturesUnordered<
         StreamUpgrade<
             THandler::InboundOpenInfo,
@@ -131,6 +132,7 @@ where
         >,
     >,
     /// Futures that upgrade outgoing substreams.
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     negotiating_out: FuturesUnordered<
         StreamUpgrade<
             THandler::OutboundOpenInfo,
@@ -155,6 +157,7 @@ where
     ///
     /// The upgrade timeout is already ticking here so this may fail in case the remote is not
     /// quick enough in providing us with a new stream.
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     requested_substreams: FuturesUnordered<
         SubstreamRequested<THandler::OutboundOpenInfo, THandler::OutboundProtocol>,
     >,
@@ -168,6 +171,7 @@ where
     stream_counter: ActiveStreamCounter,
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<THandler> fmt::Debug for Connection<THandler>
 where
     THandler: ConnectionHandler + fmt::Debug,
@@ -1189,20 +1193,13 @@ mod tests {
         type InboundOpenInfo = ();
         type OutboundOpenInfo = ();
 
-        fn listen_protocol(
-            &self,
-        ) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+        fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
             SubstreamProtocol::new(DeniedUpgrade, ()).with_timeout(self.upgrade_timeout)
         }
 
         fn on_connection_event(
             &mut self,
-            event: ConnectionEvent<
-                Self::InboundProtocol,
-                Self::OutboundProtocol,
-                Self::InboundOpenInfo,
-                Self::OutboundOpenInfo,
-            >,
+            event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
         ) {
             match event {
                 // TODO: remove when Rust 1.82 is MSRV
@@ -1242,13 +1239,7 @@ mod tests {
         fn poll(
             &mut self,
             _: &mut Context<'_>,
-        ) -> Poll<
-            ConnectionHandlerEvent<
-                Self::OutboundProtocol,
-                Self::OutboundOpenInfo,
-                Self::ToBehaviour,
-            >,
-        > {
+        ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
             if self.outbound_requested {
                 self.outbound_requested = false;
                 return Poll::Ready(ConnectionHandlerEvent::OutboundSubstreamRequest {
@@ -1269,9 +1260,7 @@ mod tests {
         type InboundOpenInfo = ();
         type OutboundOpenInfo = ();
 
-        fn listen_protocol(
-            &self,
-        ) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+        fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
             SubstreamProtocol::new(
                 ManyProtocolsUpgrade {
                     protocols: Vec::from_iter(self.active_protocols.clone()),
@@ -1282,12 +1271,7 @@ mod tests {
 
         fn on_connection_event(
             &mut self,
-            event: ConnectionEvent<
-                Self::InboundProtocol,
-                Self::OutboundProtocol,
-                Self::InboundOpenInfo,
-                Self::OutboundOpenInfo,
-            >,
+            event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
         ) {
             match event {
                 ConnectionEvent::LocalProtocolsChange(ProtocolsChange::Added(added)) => {
@@ -1319,13 +1303,7 @@ mod tests {
         fn poll(
             &mut self,
             _: &mut Context<'_>,
-        ) -> Poll<
-            ConnectionHandlerEvent<
-                Self::OutboundProtocol,
-                Self::OutboundOpenInfo,
-                Self::ToBehaviour,
-            >,
-        > {
+        ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
             if let Some(event) = self.events.pop() {
                 return Poll::Ready(event);
             }
diff --git a/swarm/src/connection/pool.rs b/swarm/src/connection/pool.rs
index 49cc774b2b7..f21a7307105 100644
--- a/swarm/src/connection/pool.rs
+++ b/swarm/src/connection/pool.rs
@@ -553,6 +553,7 @@ where
 
     /// Polls the connection pool for events.
     #[tracing::instrument(level = "debug", name = "Pool::poll", skip(self, cx))]
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     pub(crate) fn poll(&mut self, cx: &mut Context<'_>) -> Poll<PoolEvent<THandler::ToBehaviour>>
     where
         THandler: ConnectionHandler + 'static,
diff --git a/swarm/src/dummy.rs b/swarm/src/dummy.rs
index 5452c382cd4..f8137bdbeee 100644
--- a/swarm/src/dummy.rs
+++ b/swarm/src/dummy.rs
@@ -71,9 +71,9 @@ impl crate::handler::ConnectionHandler for ConnectionHandler {
     type InboundProtocol = DeniedUpgrade;
     type OutboundProtocol = DeniedUpgrade;
     type InboundOpenInfo = ();
-    type OutboundOpenInfo = Infallible;
+    type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
@@ -86,20 +86,13 @@ impl crate::handler::ConnectionHandler for ConnectionHandler {
     fn poll(
         &mut self,
         _: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         Poll::Pending
     }
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             // TODO: remove when Rust 1.82 is MSRV
diff --git a/swarm/src/handler.rs b/swarm/src/handler.rs
index 3d0407b4f70..d9293fa41de 100644
--- a/swarm/src/handler.rs
+++ b/swarm/src/handler.rs
@@ -98,6 +98,7 @@ use crate::{connection::AsStrHashEq, StreamProtocol};
 /// Implementors of this trait should keep in mind that the connection can be closed at any time.
 /// When a connection is closed gracefully, the substreams used by the handler may still
 /// continue reading data until the remote closes its side of the connection.
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 pub trait ConnectionHandler: Send + 'static {
     /// A type representing the message(s) a
     /// [`NetworkBehaviour`](crate::behaviour::NetworkBehaviour) can send to a [`ConnectionHandler`]
@@ -112,8 +113,10 @@ pub trait ConnectionHandler: Send + 'static {
     /// The outbound upgrade for the protocol(s) used by the handler.
     type OutboundProtocol: OutboundUpgradeSend;
     /// The type of additional information returned from `listen_protocol`.
+    #[deprecated = "Track data in ConnectionHandler instead."]
     type InboundOpenInfo: Send + 'static;
     /// The type of additional information passed to an `OutboundSubstreamRequest`.
+    #[deprecated = "Track data in ConnectionHandler instead."]
     type OutboundOpenInfo: Send + 'static;
 
     /// The [`InboundUpgrade`](libp2p_core::upgrade::InboundUpgrade) to apply on inbound
@@ -224,7 +227,7 @@ pub trait ConnectionHandler: Send + 'static {
 /// Enumeration with the list of the possible stream events
 /// to pass to [`on_connection_event`](ConnectionHandler::on_connection_event).
 #[non_exhaustive]
-pub enum ConnectionEvent<'a, IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IOI, OOI> {
+pub enum ConnectionEvent<'a, IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IOI = (), OOI = ()> {
     /// Informs the handler about the output of a successful upgrade on a new inbound substream.
     FullyNegotiatedInbound(FullyNegotiatedInbound<IP, IOI>),
     /// Informs the handler about the output of a successful upgrade on a new outbound stream.
@@ -318,7 +321,7 @@ impl<IP: InboundUpgradeSend, OP: OutboundUpgradeSend, IOI, OOI>
 /// [`ConnectionHandler`] implementation to stop a malicious remote node to open and keep alive
 /// an excessive amount of inbound substreams.
 #[derive(Debug)]
-pub struct FullyNegotiatedInbound<IP: InboundUpgradeSend, IOI> {
+pub struct FullyNegotiatedInbound<IP: InboundUpgradeSend, IOI = ()> {
     pub protocol: IP::Output,
     pub info: IOI,
 }
@@ -329,7 +332,7 @@ pub struct FullyNegotiatedInbound<IP: InboundUpgradeSend, IOI> {
 /// The `protocol` field is the information that was previously passed to
 /// [`ConnectionHandlerEvent::OutboundSubstreamRequest`].
 #[derive(Debug)]
-pub struct FullyNegotiatedOutbound<OP: OutboundUpgradeSend, OOI> {
+pub struct FullyNegotiatedOutbound<OP: OutboundUpgradeSend, OOI = ()> {
     pub protocol: OP::Output,
     pub info: OOI,
 }
@@ -524,7 +527,7 @@ pub struct ListenUpgradeError<IOI, IP: InboundUpgradeSend> {
 /// The inbound substream protocol(s) are defined by [`ConnectionHandler::listen_protocol`]
 /// and the outbound substream protocol(s) by [`ConnectionHandlerEvent::OutboundSubstreamRequest`].
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub struct SubstreamProtocol<TUpgrade, TInfo> {
+pub struct SubstreamProtocol<TUpgrade, TInfo = ()> {
     upgrade: TUpgrade,
     info: TInfo,
     timeout: Duration,
diff --git a/swarm/src/handler/either.rs b/swarm/src/handler/either.rs
index 1dc62e0eb2a..a349726f454 100644
--- a/swarm/src/handler/either.rs
+++ b/swarm/src/handler/either.rs
@@ -77,6 +77,7 @@ where
 
 /// Implementation of a [`ConnectionHandler`] that represents either of two [`ConnectionHandler`]
 /// implementations.
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<L, R> ConnectionHandler for Either<L, R>
 where
     L: ConnectionHandler,
diff --git a/swarm/src/handler/map_in.rs b/swarm/src/handler/map_in.rs
index 55885b351bb..7a5166cab75 100644
--- a/swarm/src/handler/map_in.rs
+++ b/swarm/src/handler/map_in.rs
@@ -47,6 +47,7 @@ impl<TConnectionHandler, TMap, TNewIn> MapInEvent<TConnectionHandler, TNewIn, TM
     }
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<TConnectionHandler, TMap, TNewIn> ConnectionHandler
     for MapInEvent<TConnectionHandler, TNewIn, TMap>
 where
diff --git a/swarm/src/handler/map_out.rs b/swarm/src/handler/map_out.rs
index 6d05551aeec..9bb0e2bc554 100644
--- a/swarm/src/handler/map_out.rs
+++ b/swarm/src/handler/map_out.rs
@@ -43,6 +43,7 @@ impl<TConnectionHandler, TMap> MapOutEvent<TConnectionHandler, TMap> {
     }
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<TConnectionHandler, TMap, TNewOut> ConnectionHandler for MapOutEvent<TConnectionHandler, TMap>
 where
     TConnectionHandler: ConnectionHandler,
diff --git a/swarm/src/handler/multi.rs b/swarm/src/handler/multi.rs
index 73af1b1109e..4f4d64f65fe 100644
--- a/swarm/src/handler/multi.rs
+++ b/swarm/src/handler/multi.rs
@@ -86,6 +86,7 @@ where
         Ok(m)
     }
 
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     fn on_listen_upgrade_error(
         &mut self,
         ListenUpgradeError {
@@ -107,6 +108,7 @@ where
     }
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<K, H> ConnectionHandler for MultiHandler<K, H>
 where
     K: Clone + Debug + Hash + Eq + Send + 'static,
diff --git a/swarm/src/handler/one_shot.rs b/swarm/src/handler/one_shot.rs
index 29f2811522b..c623008dd90 100644
--- a/swarm/src/handler/one_shot.rs
+++ b/swarm/src/handler/one_shot.rs
@@ -129,7 +129,7 @@ where
     type OutboundOpenInfo = ();
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         self.listen_protocol.clone()
     }
 
@@ -140,9 +140,7 @@ where
     fn poll(
         &mut self,
         _: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         if !self.events_out.is_empty() {
             return Poll::Ready(ConnectionHandlerEvent::NotifyBehaviour(
                 self.events_out.remove(0),
@@ -169,12 +167,7 @@ where
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
         match event {
             ConnectionEvent::FullyNegotiatedInbound(FullyNegotiatedInbound {
diff --git a/swarm/src/handler/pending.rs b/swarm/src/handler/pending.rs
index 483c4b3d6e8..8223c544593 100644
--- a/swarm/src/handler/pending.rs
+++ b/swarm/src/handler/pending.rs
@@ -51,7 +51,7 @@ impl ConnectionHandler for PendingConnectionHandler {
     type OutboundOpenInfo = Infallible;
     type InboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(PendingUpgrade::new(self.protocol_name.clone()), ())
     }
 
@@ -64,20 +64,13 @@ impl ConnectionHandler for PendingConnectionHandler {
     fn poll(
         &mut self,
         _: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, Infallible, Self::ToBehaviour>> {
         Poll::Pending
     }
 
     fn on_connection_event(
         &mut self,
-        event: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        event: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol, (), Infallible>,
     ) {
         match event {
             // TODO: remove when Rust 1.82 is MSRV
diff --git a/swarm/src/handler/select.rs b/swarm/src/handler/select.rs
index 0f6dbe988ff..f4c926f1a0e 100644
--- a/swarm/src/handler/select.rs
+++ b/swarm/src/handler/select.rs
@@ -152,6 +152,7 @@ where
     TProto1: ConnectionHandler,
     TProto2: ConnectionHandler,
 {
+    #[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
     fn on_listen_upgrade_error(
         &mut self,
         ListenUpgradeError {
@@ -181,6 +182,7 @@ where
     }
 }
 
+#[expect(deprecated)] // TODO: Remove when {In, Out}boundOpenInfo is fully removed.
 impl<TProto1, TProto2> ConnectionHandler for ConnectionHandlerSelect<TProto1, TProto2>
 where
     TProto1: ConnectionHandler,
diff --git a/swarm/tests/connection_close.rs b/swarm/tests/connection_close.rs
index bc71216870a..0d95626b2f0 100644
--- a/swarm/tests/connection_close.rs
+++ b/swarm/tests/connection_close.rs
@@ -103,7 +103,7 @@ impl ConnectionHandler for HandlerWithState {
     type InboundOpenInfo = ();
     type OutboundOpenInfo = ();
 
-    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol, Self::InboundOpenInfo> {
+    fn listen_protocol(&self) -> SubstreamProtocol<Self::InboundProtocol> {
         SubstreamProtocol::new(DeniedUpgrade, ())
     }
 
@@ -114,9 +114,7 @@ impl ConnectionHandler for HandlerWithState {
     fn poll(
         &mut self,
         _: &mut Context<'_>,
-    ) -> Poll<
-        ConnectionHandlerEvent<Self::OutboundProtocol, Self::OutboundOpenInfo, Self::ToBehaviour>,
-    > {
+    ) -> Poll<ConnectionHandlerEvent<Self::OutboundProtocol, (), Self::ToBehaviour>> {
         Poll::Pending
     }
 
@@ -137,12 +135,7 @@ impl ConnectionHandler for HandlerWithState {
 
     fn on_connection_event(
         &mut self,
-        _: ConnectionEvent<
-            Self::InboundProtocol,
-            Self::OutboundProtocol,
-            Self::InboundOpenInfo,
-            Self::OutboundOpenInfo,
-        >,
+        _: ConnectionEvent<Self::InboundProtocol, Self::OutboundProtocol>,
     ) {
     }
 }