diff --git a/ruma-client-api/src/r0/context/get_context.rs b/ruma-client-api/src/r0/context/get_context.rs
index 1d51ce4e..38f5833e 100644
--- a/ruma-client-api/src/r0/context/get_context.rs
+++ b/ruma-client-api/src/r0/context/get_context.rs
@@ -18,14 +18,15 @@ ruma_api! {
         requires_authentication: true,
     }
 
+    #[non_exhaustive]
     request: {
         /// The room to get events from.
         #[ruma_api(path)]
-        pub room_id: RoomId,
+        pub room_id: &'a RoomId,
 
         /// The event to get context around.
         #[ruma_api(path)]
-        pub event_id: EventId,
+        pub event_id: &'a EventId,
 
         /// The maximum number of events to return.
         ///
@@ -44,6 +45,7 @@ ruma_api! {
         pub filter: Option<RoomEventFilter>,
     }
 
+    #[non_exhaustive]
     response: {
         /// A token that can be used to paginate backwards with.
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -75,6 +77,27 @@ ruma_api! {
     error: crate::Error
 }
 
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given room id and event id.
+    pub fn new(room_id: &'a RoomId, event_id: &'a EventId) -> Self {
+        Self { room_id, event_id, limit: default_limit(), filter: None }
+    }
+}
+
+impl Response {
+    /// Creates an empty `Response`.
+    pub fn new() -> Self {
+        Self {
+            start: None,
+            end: None,
+            events_before: Vec::new(),
+            event: None,
+            events_after: Vec::new(),
+            state: Vec::new(),
+        }
+    }
+}
+
 fn default_limit() -> UInt {
     uint!(10)
 }
diff --git a/ruma-client-api/src/r0/filter/create_filter.rs b/ruma-client-api/src/r0/filter/create_filter.rs
index 61daa97b..b37ca3f5 100644
--- a/ruma-client-api/src/r0/filter/create_filter.rs
+++ b/ruma-client-api/src/r0/filter/create_filter.rs
@@ -15,18 +15,20 @@ ruma_api! {
         requires_authentication: true,
     }
 
+    #[non_exhaustive]
     request: {
         /// The ID of the user uploading the filter.
         ///
         /// The access token must be authorized to make requests for this user ID.
         #[ruma_api(path)]
-        pub user_id: UserId,
+        pub user_id: &'a UserId,
 
         /// The filter definition.
         #[ruma_api(body)]
         pub filter: FilterDefinition,
     }
 
+    #[non_exhaustive]
     response: {
         /// The ID of the filter that was created.
         pub filter_id: String,
@@ -34,3 +36,17 @@ ruma_api! {
 
     error: crate::Error
 }
+
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given user ID and filter definition.
+    pub fn new(user_id: &'a UserId, filter: FilterDefinition) -> Self {
+        Self { user_id, filter }
+    }
+}
+
+impl Response {
+    /// Creates a new `Response` with the given filter ID.
+    pub fn new(filter_id: String) -> Self {
+        Self { filter_id }
+    }
+}
diff --git a/ruma-client-api/src/r0/filter/get_filter.rs b/ruma-client-api/src/r0/filter/get_filter.rs
index e7684490..87b69f1b 100644
--- a/ruma-client-api/src/r0/filter/get_filter.rs
+++ b/ruma-client-api/src/r0/filter/get_filter.rs
@@ -15,16 +15,18 @@ ruma_api! {
         requires_authentication: true,
     }
 
+    #[non_exhaustive]
     request: {
         /// The user ID to download a filter for.
         #[ruma_api(path)]
-        pub user_id: UserId,
+        pub user_id: &'a UserId,
 
         /// The ID of the filter to download.
         #[ruma_api(path)]
-        pub filter_id: String,
+        pub filter_id: &'a str,
     }
 
+    #[non_exhaustive]
     response: {
         /// The filter definition.
         #[ruma_api(body)]
@@ -33,3 +35,17 @@ ruma_api! {
 
     error: crate::Error
 }
+
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given user ID and filter ID.
+    pub fn new(user_id: &'a UserId, filter_id: &'a str) -> Self {
+        Self { user_id, filter_id }
+    }
+}
+
+impl Response {
+    /// Creates a new `Response` with the given filter definition.
+    pub fn new(filter: FilterDefinition) -> Self {
+        Self { filter }
+    }
+}
diff --git a/ruma-client-api/src/r0/message/get_message_events.rs b/ruma-client-api/src/r0/message/get_message_events.rs
index a6ed4159..3427fcbb 100644
--- a/ruma-client-api/src/r0/message/get_message_events.rs
+++ b/ruma-client-api/src/r0/message/get_message_events.rs
@@ -23,7 +23,7 @@ ruma_api! {
     request: {
         /// The room to get events from.
         #[ruma_api(path)]
-        pub room_id: RoomId,
+        pub room_id: &'a RoomId,
 
         /// The token to start returning events from.
         ///
@@ -31,7 +31,7 @@ ruma_api! {
         /// prev_batch token returned for each room by the sync API, or from a start or end token
         /// returned by a previous request to this endpoint.
         #[ruma_api(query)]
-        pub from: String,
+        pub from: &'a str,
 
         /// The token to stop returning events at.
         ///
@@ -40,7 +40,7 @@ ruma_api! {
         /// by a previous request to this endpoint.
         #[serde(skip_serializing_if = "Option::is_none")]
         #[ruma_api(query)]
-        pub to: Option<String>,
+        pub to: Option<&'a str>,
 
         /// The direction to return events from.
         #[ruma_api(query)]
@@ -63,6 +63,7 @@ ruma_api! {
         pub filter: Option<RoomEventFilter>,
     }
 
+    #[non_exhaustive]
     response: {
         /// The token the pagination starts from.
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -84,15 +85,22 @@ ruma_api! {
     error: crate::Error
 }
 
-impl Request {
+impl<'a> Request<'a> {
     /// Creates a `Request` with the given parameters.
     ///
     /// All other parameters will be defaulted.
-    pub fn new(room_id: RoomId, from: String, dir: Direction) -> Self {
+    pub fn new(room_id: &'a RoomId, from: &'a str, dir: Direction) -> Self {
         Self { room_id, from, to: None, dir, limit: default_limit(), filter: None }
     }
 }
 
+impl Response {
+    /// Creates an empty `Response`.
+    pub fn new() -> Self {
+        Self { start: None, end: None, chunk: Vec::new(), state: Vec::new() }
+    }
+}
+
 fn default_limit() -> UInt {
     uint!(10)
 }
@@ -135,9 +143,9 @@ mod tests {
             ..Default::default()
         };
         let req = Request {
-            room_id,
-            from: "token".into(),
-            to: Some("token2".into()),
+            room_id: &room_id,
+            from: "token",
+            to: Some("token2"),
             dir: Direction::Backward,
             limit: uint!(0),
             filter: Some(filter),
@@ -161,9 +169,9 @@ mod tests {
     fn test_serialize_none_room_event_filter() {
         let room_id = room_id!("!roomid:example.org");
         let req = Request {
-            room_id,
-            from: "token".into(),
-            to: Some("token2".into()),
+            room_id: &room_id,
+            from: "token",
+            to: Some("token2"),
             dir: Direction::Backward,
             limit: uint!(0),
             filter: None,
@@ -178,9 +186,9 @@ mod tests {
     fn test_serialize_default_room_event_filter() {
         let room_id = room_id!("!roomid:example.org");
         let req = Request {
-            room_id,
-            from: "token".into(),
-            to: Some("token2".into()),
+            room_id: &room_id,
+            from: "token",
+            to: Some("token2"),
             dir: Direction::Backward,
             limit: uint!(0),
             filter: Some(RoomEventFilter::default()),
diff --git a/ruma-client-api/src/r0/search/search_events.rs b/ruma-client-api/src/r0/search/search_events.rs
index 9237bf99..65117056 100644
--- a/ruma-client-api/src/r0/search/search_events.rs
+++ b/ruma-client-api/src/r0/search/search_events.rs
@@ -3,7 +3,7 @@
 use std::collections::BTreeMap;
 
 use js_int::{uint, UInt};
-use ruma_api::ruma_api;
+use ruma_api::{ruma_api, Outgoing};
 use ruma_common::Raw;
 use ruma_events::{AnyEvent, AnyStateEvent};
 use ruma_identifiers::{EventId, RoomId, UserId};
@@ -21,17 +21,19 @@ ruma_api! {
         requires_authentication: true,
     }
 
+    #[non_exhaustive]
     request: {
         /// The point to return events from.
         ///
         /// If given, this should be a `next_batch` result from a previous call to this endpoint.
         #[ruma_api(query)]
-        pub next_batch: Option<String>,
+        pub next_batch: Option<&'a str>,
 
         /// Describes which categories to search in and their criteria.
-        pub search_categories: Categories,
+        pub search_categories: Categories<'a>,
     }
 
+    #[non_exhaustive]
     response: {
         /// A grouping of search results by category.
         pub search_categories: ResultCategories,
@@ -40,23 +42,45 @@ ruma_api! {
     error: crate::Error
 }
 
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given categories.
+    pub fn new(search_categories: Categories<'a>) -> Self {
+        Self { next_batch: None, search_categories }
+    }
+}
+
+impl Response {
+    /// Creates a new `Response` with the given search results.
+    pub fn new(search_categories: ResultCategories) -> Self {
+        Self { search_categories }
+    }
+}
+
 /// Categories of events that can be searched for.
-#[derive(Clone, Debug, Deserialize, Serialize)]
-pub struct Categories {
-    /// Criteria for searching a category of events.
+#[derive(Clone, Debug, Outgoing, Serialize)]
+#[non_exhaustive]
+pub struct Categories<'a> {
+    /// Criteria for searching room events.
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub room_events: Option<Criteria>,
+    pub room_events: Option<Criteria<'a>>,
+}
+
+impl<'a> Categories<'a> {
+    /// Creates an empty `Categories`.
+    pub fn new() -> Self {
+        Self { room_events: None }
+    }
 }
 
 /// Criteria for searching a category of events.
-#[derive(Clone, Debug, Deserialize, Serialize)]
-pub struct Criteria {
+#[derive(Clone, Debug, Outgoing, Serialize)]
+pub struct Criteria<'a> {
     /// The string to search events for.
-    pub search_term: String,
+    pub search_term: &'a str,
 
     /// The keys to search for. Defaults to all keys.
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub keys: Option<Vec<SearchKeys>>,
+    pub keys: Option<&'a [SearchKeys]>,
 
     /// A `Filter` to apply to the search.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -76,7 +100,7 @@ pub struct Criteria {
 
     /// Requests that the server partitions the result set based on the provided list of keys.
     #[serde(skip_serializing_if = "Option::is_none")]
-    pub groupings: Option<Groupings>,
+    pub groupings: Option<Groupings<'a>>,
 }
 
 /// Configures whether any context for the events returned are included in the response.
@@ -154,11 +178,11 @@ pub enum GroupingKey {
 }
 
 /// Requests that the server partitions the result set based on the provided list of keys.
-#[derive(Clone, Debug, Deserialize, Serialize)]
-pub struct Groupings {
+#[derive(Clone, Copy, Debug, Outgoing, Serialize)]
+pub struct Groupings<'a> {
     /// List of groups to request.
-    #[serde(default, skip_serializing_if = "Vec::is_empty")]
-    pub group_by: Vec<Grouping>,
+    #[serde(default, skip_serializing_if = "<[_]>::is_empty")]
+    pub group_by: &'a [Grouping],
 }
 
 /// The keys to search for.
diff --git a/ruma-client-api/src/r0/server/get_user_info.rs b/ruma-client-api/src/r0/server/get_user_info.rs
index 02a2367b..134497c2 100644
--- a/ruma-client-api/src/r0/server/get_user_info.rs
+++ b/ruma-client-api/src/r0/server/get_user_info.rs
@@ -16,12 +16,14 @@ ruma_api! {
         requires_authentication: true,
     }
 
+    #[non_exhaustive]
     request: {
         /// The user to look up.
         #[ruma_api(path)]
-        pub user_id: UserId,
+        pub user_id: &'a UserId,
     }
 
+    #[non_exhaustive]
     response: {
         /// The Matrix user ID of the user.
         #[serde(skip_serializing_if = "Option::is_none")]
@@ -35,6 +37,20 @@ ruma_api! {
     error: crate::Error
 }
 
+impl<'a> Request<'a> {
+    /// Creates a new `Request` with the given user id.
+    pub fn new(user_id: &'a UserId) -> Self {
+        Self { user_id }
+    }
+}
+
+impl Response {
+    /// Creates an empty `Response`.
+    pub fn new() -> Self {
+        Self { user_id: None, devices: BTreeMap::new() }
+    }
+}
+
 /// Information about a user's device.
 #[derive(Clone, Debug, Deserialize, Serialize)]
 pub struct DeviceInfo {
diff --git a/ruma-client-api/src/r0/session/login.rs b/ruma-client-api/src/r0/session/login.rs
index 0513cf8e..1aaf2182 100644
--- a/ruma-client-api/src/r0/session/login.rs
+++ b/ruma-client-api/src/r0/session/login.rs
@@ -64,7 +64,7 @@ ruma_api! {
 }
 
 /// Identification information for the user.
-#[derive(Clone, Debug, PartialEq, Eq, Outgoing, Serialize)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Outgoing, Serialize)]
 #[serde(from = "user_serde::IncomingUserInfo", into = "user_serde::UserInfo")]
 pub enum UserInfo<'a> {
     /// Either a fully qualified Matrix user ID, or just the localpart (as part of the 'identifier'
@@ -92,7 +92,7 @@ pub enum UserInfo<'a> {
 }
 
 /// The authentication mechanism.
-#[derive(Clone, Debug, PartialEq, Eq, Outgoing, Serialize)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Outgoing, Serialize)]
 #[serde(tag = "type")]
 pub enum LoginInfo<'a> {
     /// A password is supplied to authenticate.
diff --git a/ruma-client-api/src/r0/sync/sync_events.rs b/ruma-client-api/src/r0/sync/sync_events.rs
index 8f62e233..c4bea870 100644
--- a/ruma-client-api/src/r0/sync/sync_events.rs
+++ b/ruma-client-api/src/r0/sync/sync_events.rs
@@ -3,7 +3,7 @@
 use std::{collections::BTreeMap, time::Duration};
 
 use js_int::UInt;
-use ruma_api::ruma_api;
+use ruma_api::{ruma_api, Outgoing};
 use ruma_common::{presence::PresenceState, Raw};
 use ruma_events::{
     presence::PresenceEvent, AnyBasicEvent, AnyStrippedStateEvent, AnySyncEphemeralRoomEvent,
@@ -28,7 +28,7 @@ ruma_api! {
         /// A filter represented either as its full JSON definition or the ID of a saved filter.
         #[serde(skip_serializing_if = "Option::is_none")]
         #[ruma_api(query)]
-        pub filter: Option<Filter>,
+        pub filter: Option<Filter<'a>>,
 
         /// A point in time to continue a sync from.
         ///
@@ -36,7 +36,7 @@ ruma_api! {
         /// request.
         #[serde(skip_serializing_if = "Option::is_none")]
         #[ruma_api(query)]
-        pub since: Option<String>,
+        pub since: Option<&'a str>,
 
         /// Controls whether to include the full state for all rooms the user is a member of.
         #[serde(default, skip_serializing_if = "ruma_serde::is_default")]
@@ -94,10 +94,10 @@ ruma_api! {
 }
 
 /// A filter represented either as its full JSON definition or the ID of a saved filter.
-#[derive(Clone, Debug, Deserialize, Serialize)]
+#[derive(Clone, Debug, Outgoing, Serialize)]
 #[allow(clippy::large_enum_variant)]
 #[serde(untagged)]
-pub enum Filter {
+pub enum Filter<'a> {
     // The filter definition needs to be (de)serialized twice because it is a URL-encoded JSON
     // string. Since #[ruma_api(query)] only does the latter and this is a very uncommon
     // setup, we implement it through custom serde logic for this specific enum variant rather than
@@ -113,7 +113,7 @@ pub enum Filter {
     FilterDefinition(FilterDefinition),
 
     /// The ID of a filter saved on the server.
-    FilterId(String),
+    FilterId(&'a str),
 }
 
 /// Updates to rooms.
@@ -408,13 +408,13 @@ mod tests {
 
     use matches::assert_matches;
 
-    use super::{Filter, PresenceState, Request, Timeline};
+    use super::{Filter, IncomingFilter, IncomingRequest, PresenceState, Request, Timeline};
 
     #[test]
     fn serialize_all_params() {
         let req: http::Request<Vec<u8>> = Request {
-            filter: Some(Filter::FilterId("66696p746572".into())),
-            since: Some("s72594_4483_1934".into()),
+            filter: Some(Filter::FilterId("66696p746572")),
+            since: Some("s72594_4483_1934"),
             full_state: true,
             set_presence: PresenceState::Offline,
             timeout: Some(Duration::from_millis(30000)),
@@ -449,10 +449,10 @@ mod tests {
             .build()
             .unwrap();
 
-        let req: Request =
+        let req: IncomingRequest =
             http::Request::builder().uri(uri).body(Vec::<u8>::new()).unwrap().try_into().unwrap();
 
-        assert_matches!(req.filter, Some(Filter::FilterId(id)) if id == "myfilter");
+        assert_matches!(req.filter, Some(IncomingFilter::FilterId(id)) if id == "myfilter");
         assert_eq!(req.since, Some("myts".into()));
         assert_eq!(req.full_state, false);
         assert_eq!(req.set_presence, PresenceState::Offline);
@@ -468,7 +468,7 @@ mod tests {
             .build()
             .unwrap();
 
-        let req: Request =
+        let req: IncomingRequest =
             http::Request::builder().uri(uri).body(Vec::<u8>::new()).unwrap().try_into().unwrap();
 
         assert_matches!(req.filter, None);
@@ -491,10 +491,10 @@ mod tests {
             .build()
             .unwrap();
 
-        let req: Request =
+        let req: IncomingRequest =
             http::Request::builder().uri(uri).body(Vec::<u8>::new()).unwrap().try_into().unwrap();
 
-        assert_matches!(req.filter, Some(Filter::FilterId(id)) if id == "EOKFFmdZYF");
+        assert_matches!(req.filter, Some(IncomingFilter::FilterId(id)) if id == "EOKFFmdZYF");
         assert_eq!(req.since, None);
         assert_eq!(req.full_state, false);
         assert_eq!(req.set_presence, PresenceState::Online);
diff --git a/ruma-client/src/lib.rs b/ruma-client/src/lib.rs
index 58dacbcf..b47e1ea8 100644
--- a/ruma-client/src/lib.rs
+++ b/ruma-client/src/lib.rs
@@ -319,24 +319,25 @@ where
     /// If the since parameter is None, the first Item might take a significant time to arrive and
     /// be deserialized, because it contains all events that have occurred in the whole lifetime of
     /// the logged-in users account and are visible to them.
-    pub fn sync(
+    pub fn sync<'a>(
         &self,
-        filter: Option<SyncFilter>,
+        filter: Option<SyncFilter<'a>>,
         since: Option<String>,
         set_presence: ruma_common::presence::PresenceState,
         timeout: Option<Duration>,
     ) -> impl Stream<Item = Result<SyncResponse, Error<ruma_client_api::Error>>>
-           + TryStream<Ok = SyncResponse, Error = Error<ruma_client_api::Error>> {
+           + TryStream<Ok = SyncResponse, Error = Error<ruma_client_api::Error>>
+           + 'a {
         let client = self.clone();
         stream::try_unfold(since, move |since| {
             let client = client.clone();
-            let filter = filter.clone();
+            let filter = filter.clone(); // FIXME: Remove once `SyncFilter` is `Copy`
 
             async move {
                 let response = client
                     .request(SyncRequest {
                         filter,
-                        since,
+                        since: since.as_deref(),
                         full_state: false,
                         set_presence,
                         timeout,