diff --git a/crates/ruma-common/CHANGELOG.md b/crates/ruma-common/CHANGELOG.md
index 44f96d9c..81d5f367 100644
--- a/crates/ruma-common/CHANGELOG.md
+++ b/crates/ruma-common/CHANGELOG.md
@@ -13,6 +13,8 @@ Improvements:
 * Stabilize default room server ACL push rule
 * Stabilize `room_types` in `directory::Filter` and `room_type` in `directory::PublicRoomsChunk`
 * Stabilize support for private read receipts
+* Add stable support for threads
+  * Move `Relation::Thread` and associated types and methods out of `unstable-msc3440`
 
 # 0.10.3
 
diff --git a/crates/ruma-common/Cargo.toml b/crates/ruma-common/Cargo.toml
index ebf052d3..10316960 100644
--- a/crates/ruma-common/Cargo.toml
+++ b/crates/ruma-common/Cargo.toml
@@ -38,7 +38,6 @@ unstable-msc2870 = []
 unstable-msc3245 = ["unstable-msc3246"]
 unstable-msc3246 = ["unstable-msc3551", "dep:thiserror"]
 unstable-msc3381 = ["unstable-msc1767"]
-unstable-msc3440 = []
 unstable-msc3488 = ["unstable-msc1767"]
 unstable-msc3551 = ["unstable-msc1767"]
 unstable-msc3552 = ["unstable-msc3551"]
diff --git a/crates/ruma-common/src/events/relation.rs b/crates/ruma-common/src/events/relation.rs
index 1f06222f..10aa2cfe 100644
--- a/crates/ruma-common/src/events/relation.rs
+++ b/crates/ruma-common/src/events/relation.rs
@@ -4,17 +4,16 @@
 
 use std::fmt::Debug;
 
-#[cfg(any(feature = "unstable-msc2677", feature = "unstable-msc3440"))]
 use js_int::UInt;
 use serde::{Deserialize, Serialize};
 
-#[cfg(feature = "unstable-msc3440")]
-use super::AnySyncMessageLikeEvent;
-#[cfg(feature = "unstable-msc3440")]
-use crate::serde::Raw;
+use super::AnyMessageLikeEvent;
 #[cfg(any(feature = "unstable-msc2676", feature = "unstable-msc2677"))]
 use crate::MilliSecondsSinceUnixEpoch;
-use crate::{serde::StringEnum, PrivOwnedStr};
+use crate::{
+    serde::{Raw, StringEnum},
+    PrivOwnedStr,
+};
 #[cfg(feature = "unstable-msc2676")]
 use crate::{OwnedEventId, OwnedUserId};
 
@@ -112,11 +111,10 @@ impl BundledReplacement {
 
 /// A bundled thread.
 #[derive(Clone, Debug, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
 pub struct BundledThread {
     /// The latest event in the thread.
-    pub latest_event: Box<Raw<AnySyncMessageLikeEvent>>,
+    pub latest_event: Box<Raw<AnyMessageLikeEvent>>,
 
     /// The number of events in the thread.
     pub count: UInt,
@@ -125,11 +123,10 @@ pub struct BundledThread {
     pub current_user_participated: bool,
 }
 
-#[cfg(feature = "unstable-msc3440")]
 impl BundledThread {
     /// Creates a new `BundledThread` with the given event, count and user participated flag.
     pub fn new(
-        latest_event: Box<Raw<AnySyncMessageLikeEvent>>,
+        latest_event: Box<Raw<AnyMessageLikeEvent>>,
         count: UInt,
         current_user_participated: bool,
     ) -> Self {
@@ -154,8 +151,7 @@ pub struct Relations {
     pub replace: Option<BundledReplacement>,
 
     /// Thread relation.
-    #[cfg(feature = "unstable-msc3440")]
-    #[serde(rename = "io.element.thread", alias = "m.thread")]
+    #[serde(rename = "m.thread")]
     pub thread: Option<BundledThread>,
 }
 
@@ -182,8 +178,7 @@ pub enum RelationType {
     Replacement,
 
     /// `m.thread`, a participant to a thread.
-    #[cfg(feature = "unstable-msc3440")]
-    #[ruma_enum(rename = "io.element.thread", alias = "m.thread")]
+    #[ruma_enum(rename = "m.thread")]
     Thread,
 
     #[doc(hidden)]
diff --git a/crates/ruma-common/src/events/room/encrypted.rs b/crates/ruma-common/src/events/room/encrypted.rs
index 5f6f5e2e..62149fe4 100644
--- a/crates/ruma-common/src/events/room/encrypted.rs
+++ b/crates/ruma-common/src/events/room/encrypted.rs
@@ -102,7 +102,6 @@ pub enum Relation {
     Annotation(Annotation),
 
     /// An event that belongs to a thread.
-    #[cfg(feature = "unstable-msc3440")]
     Thread(Thread),
 
     #[doc(hidden)]
@@ -117,7 +116,6 @@ impl From<message::Relation> for Relation {
             message::Relation::Replacement(re) => {
                 Self::Replacement(Replacement { event_id: re.event_id })
             }
-            #[cfg(feature = "unstable-msc3440")]
             message::Relation::Thread(t) => Self::Thread(Thread {
                 event_id: t.event_id,
                 in_reply_to: t.in_reply_to,
@@ -178,7 +176,6 @@ impl Annotation {
 
 /// A thread relation for an event.
 #[derive(Clone, Debug, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
 pub struct Thread {
     /// The ID of the root message in the thread.
@@ -199,7 +196,6 @@ pub struct Thread {
     pub is_falling_back: bool,
 }
 
-#[cfg(feature = "unstable-msc3440")]
 impl Thread {
     /// Convenience method to create a regular `Thread` with the given event ID and latest
     /// message-like event ID.
diff --git a/crates/ruma-common/src/events/room/encrypted/relation_serde.rs b/crates/ruma-common/src/events/room/encrypted/relation_serde.rs
index e12287ef..ecea6027 100644
--- a/crates/ruma-common/src/events/room/encrypted/relation_serde.rs
+++ b/crates/ruma-common/src/events/room/encrypted/relation_serde.rs
@@ -4,10 +4,7 @@ use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use super::Annotation;
 #[cfg(feature = "unstable-msc2676")]
 use super::Replacement;
-#[cfg(feature = "unstable-msc3440")]
-use super::Thread;
-use super::{InReplyTo, Reference, Relation};
-#[cfg(feature = "unstable-msc3440")]
+use super::{InReplyTo, Reference, Relation, Thread};
 use crate::OwnedEventId;
 
 impl<'de> Deserialize<'de> for Relation {
@@ -17,7 +14,6 @@ impl<'de> Deserialize<'de> for Relation {
     {
         let ev = EventWithRelatesToJsonRepr::deserialize(deserializer)?;
 
-        #[cfg(feature = "unstable-msc3440")]
         if let Some(
             RelationJsonRepr::ThreadStable(ThreadStableJsonRepr { event_id, is_falling_back })
             | RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr { event_id, is_falling_back }),
@@ -40,7 +36,6 @@ impl<'de> Deserialize<'de> for Relation {
                 RelationJsonRepr::Replacement(Replacement { event_id }) => {
                     Relation::Replacement(Replacement { event_id })
                 }
-                #[cfg(feature = "unstable-msc3440")]
                 RelationJsonRepr::ThreadStable(_) | RelationJsonRepr::ThreadUnstable(_) => {
                     unreachable!()
                 }
@@ -80,11 +75,10 @@ impl Serialize for Relation {
             Relation::Reply { in_reply_to } => {
                 RelatesToJsonRepr { in_reply_to: Some(in_reply_to.clone()), ..Default::default() }
             }
-            #[cfg(feature = "unstable-msc3440")]
             Relation::Thread(Thread { event_id, in_reply_to, is_falling_back }) => {
                 RelatesToJsonRepr {
                     in_reply_to: Some(in_reply_to.clone()),
-                    relation: Some(RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr {
+                    relation: Some(RelationJsonRepr::ThreadStable(ThreadStableJsonRepr {
                         event_id: event_id.clone(),
                         is_falling_back: *is_falling_back,
                     })),
@@ -123,7 +117,6 @@ impl RelatesToJsonRepr {
 
 /// A thread relation without the reply fallback, with stable names.
 #[derive(Clone, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 struct ThreadStableJsonRepr {
     /// The ID of the root message in the thread.
     pub event_id: OwnedEventId,
@@ -136,7 +129,6 @@ struct ThreadStableJsonRepr {
 
 /// A thread relation without the reply fallback, with unstable names.
 #[derive(Clone, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 struct ThreadUnstableJsonRepr {
     /// The ID of the root message in the thread.
     pub event_id: OwnedEventId,
@@ -170,12 +162,10 @@ enum RelationJsonRepr {
     Replacement(Replacement),
 
     /// An event that belongs to a thread, with stable names.
-    #[cfg(feature = "unstable-msc3440")]
     #[serde(rename = "m.thread")]
     ThreadStable(ThreadStableJsonRepr),
 
     /// An event that belongs to a thread, with unstable names.
-    #[cfg(feature = "unstable-msc3440")]
     #[serde(rename = "io.element.thread")]
     ThreadUnstable(ThreadUnstableJsonRepr),
 
diff --git a/crates/ruma-common/src/events/room/message.rs b/crates/ruma-common/src/events/room/message.rs
index 8220f146..dd350ad0 100644
--- a/crates/ruma-common/src/events/room/message.rs
+++ b/crates/ruma-common/src/events/room/message.rs
@@ -166,7 +166,6 @@ impl RoomMessageEventContent {
     /// If `message` is a text, an emote or a notice message, it is modified to include the rich
     /// reply fallback.
     #[doc = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/src/doc/rich_reply.md"))]
-    #[cfg(feature = "unstable-msc3440")]
     pub fn reply(
         message: MessageType,
         original_message: &OriginalRoomMessageEvent,
@@ -198,7 +197,7 @@ impl RoomMessageEventContent {
             .as_ref()
             .filter(|_| forward_thread == ForwardThread::Yes)
         {
-            Relation::Thread(Thread::reply(event_id.clone(), original_message.event_id.clone()))
+            Relation::Thread(Thread::plain(event_id.clone(), original_message.event_id.clone()))
         } else {
             Relation::Reply {
                 in_reply_to: InReplyTo { event_id: original_message.event_id.clone() },
@@ -217,17 +216,16 @@ impl RoomMessageEventContent {
     /// If `message` is a text, an emote or a notice message, and this is a reply in the thread, it
     /// is modified to include the rich reply fallback.
     #[doc = include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/src/doc/rich_reply.md"))]
-    #[cfg(feature = "unstable-msc3440")]
     pub fn for_thread(
         message: MessageType,
         previous_message: &OriginalRoomMessageEvent,
-        is_reply: ReplyInThread,
+        is_reply: ReplyWithinThread,
     ) -> Self {
         let make_reply = |body, formatted: Option<FormattedBody>| {
             reply::plain_and_formatted_reply_body(body, formatted.map(|f| f.body), previous_message)
         };
 
-        let msgtype = if is_reply == ReplyInThread::Yes {
+        let msgtype = if is_reply == ReplyWithinThread::Yes {
             // If this is a real reply, add the rich reply fallback.
             match message {
                 MessageType::Text(TextMessageEventContent { body, formatted, .. }) => {
@@ -261,7 +259,7 @@ impl RoomMessageEventContent {
             relates_to: Some(Relation::Thread(Thread {
                 event_id: thread_root,
                 in_reply_to: InReplyTo { event_id: previous_message.event_id.clone() },
-                is_falling_back: is_reply == ReplyInThread::No,
+                is_falling_back: is_reply == ReplyWithinThread::No,
             })),
         }
     }
@@ -314,15 +312,15 @@ impl RoomMessageEventContent {
 }
 
 /// Whether or not to forward a [`Relation::Thread`] when sending a reply.
-#[cfg(feature = "unstable-msc3440")]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 #[allow(clippy::exhaustive_enums)]
 pub enum ForwardThread {
     /// The thread relation in the original message is forwarded if it exists.
     ///
-    /// This should be set if your client doesn't support threads (see [MSC3440]).
+    /// This should be set if your client doesn't render threads (see the [info
+    /// box for clients which are acutely aware of threads]).
     ///
-    /// [MSC3440]: https://github.com/matrix-org/matrix-spec-proposals/pull/3440
+    /// [info box for clients which are acutely aware of threads]: https://spec.matrix.org/v1.4/client-server-api/#fallback-for-unthreaded-clients
     Yes,
 
     /// Create a reply in the main conversation even if the original message is in a thread.
@@ -332,20 +330,21 @@ pub enum ForwardThread {
 }
 
 /// Whether or not the message is a reply inside a thread.
-#[cfg(feature = "unstable-msc3440")]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 #[allow(clippy::exhaustive_enums)]
-pub enum ReplyInThread {
+pub enum ReplyWithinThread {
     /// This is a reply.
     ///
-    /// Create a proper reply _in_ the thread.
+    /// Create a [reply within the thread].
+    ///
+    /// [reply within the thread]: https://spec.matrix.org/v1.4/client-server-api/#replies-within-threads
     Yes,
 
     /// This is not a reply.
     ///
-    /// Create a regular message in the thread, with a reply fallback, according to [MSC3440].
+    /// Create a regular message in the thread, with a [fallback for unthreaded clients].
     ///
-    /// [MSC3440]: https://github.com/matrix-org/matrix-spec-proposals/pull/3440
+    /// [fallback for unthreaded clients]: https://spec.matrix.org/v1.4/client-server-api/#fallback-for-unthreaded-clients
     No,
 }
 
@@ -520,7 +519,6 @@ pub enum Relation {
     Replacement(Replacement),
 
     /// An event that belongs to a thread.
-    #[cfg(feature = "unstable-msc3440")]
     Thread(Thread),
 
     #[doc(hidden)]
@@ -564,7 +562,6 @@ impl Replacement {
 
 /// The content of a thread relation.
 #[derive(Clone, Debug, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 #[cfg_attr(not(feature = "unstable-exhaustive-types"), non_exhaustive)]
 pub struct Thread {
     /// The ID of the root message in the thread.
@@ -585,7 +582,6 @@ pub struct Thread {
     pub is_falling_back: bool,
 }
 
-#[cfg(feature = "unstable-msc3440")]
 impl Thread {
     /// Convenience method to create a regular `Thread` with the given event ID and latest
     /// message-like event ID.
diff --git a/crates/ruma-common/src/events/room/message/relation_serde.rs b/crates/ruma-common/src/events/room/message/relation_serde.rs
index c68d4b67..1afd392d 100644
--- a/crates/ruma-common/src/events/room/message/relation_serde.rs
+++ b/crates/ruma-common/src/events/room/message/relation_serde.rs
@@ -4,10 +4,7 @@ use serde::{Deserialize, Deserializer, Serialize, Serializer};
 use super::Replacement;
 #[cfg(feature = "unstable-msc2676")]
 use super::RoomMessageEventContent;
-#[cfg(feature = "unstable-msc3440")]
-use super::Thread;
-use super::{InReplyTo, Relation};
-#[cfg(any(feature = "unstable-msc2676", feature = "unstable-msc3440"))]
+use super::{InReplyTo, Relation, Thread};
 use crate::OwnedEventId;
 
 impl<'de> Deserialize<'de> for Relation {
@@ -17,7 +14,6 @@ impl<'de> Deserialize<'de> for Relation {
     {
         let ev = EventWithRelatesToJsonRepr::deserialize(deserializer)?;
 
-        #[cfg(feature = "unstable-msc3440")]
         if let Some(
             RelationJsonRepr::ThreadStable(ThreadStableJsonRepr { event_id, is_falling_back })
             | RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr { event_id, is_falling_back }),
@@ -44,7 +40,6 @@ impl<'de> Deserialize<'de> for Relation {
                 // FIXME: Maybe we should log this, though at this point we don't even have
                 // access to the rel_type of the unknown relation.
                 RelationJsonRepr::Unknown => Relation::_Custom,
-                #[cfg(feature = "unstable-msc3440")]
                 RelationJsonRepr::ThreadStable(_) | RelationJsonRepr::ThreadUnstable(_) => {
                     unreachable!()
                 }
@@ -80,11 +75,10 @@ impl Serialize for Relation {
                     new_content: Some(new_content.clone()),
                 }
             }
-            #[cfg(feature = "unstable-msc3440")]
             Relation::Thread(Thread { event_id, in_reply_to, is_falling_back }) => {
                 EventWithRelatesToJsonRepr::new(RelatesToJsonRepr {
                     in_reply_to: Some(in_reply_to.clone()),
-                    relation: Some(RelationJsonRepr::ThreadUnstable(ThreadUnstableJsonRepr {
+                    relation: Some(RelationJsonRepr::ThreadStable(ThreadStableJsonRepr {
                         event_id: event_id.clone(),
                         is_falling_back: *is_falling_back,
                     })),
@@ -144,13 +138,11 @@ enum RelationJsonRepr {
     #[serde(rename = "m.replace")]
     Replacement(ReplacementJsonRepr),
 
-    /// An event that belongs to a thread, with unstable names.
-    #[cfg(feature = "unstable-msc3440")]
+    /// An event that belongs to a thread, with stable names.
     #[serde(rename = "m.thread")]
     ThreadStable(ThreadStableJsonRepr),
 
     /// An event that belongs to a thread, with unstable names.
-    #[cfg(feature = "unstable-msc3440")]
     #[serde(rename = "io.element.thread")]
     ThreadUnstable(ThreadUnstableJsonRepr),
 
@@ -170,7 +162,6 @@ struct ReplacementJsonRepr {
 
 /// A thread relation without the reply fallback, with stable names.
 #[derive(Clone, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 struct ThreadStableJsonRepr {
     /// The ID of the root message in the thread.
     event_id: OwnedEventId,
@@ -183,7 +174,6 @@ struct ThreadStableJsonRepr {
 
 /// A thread relation without the reply fallback, with unstable names.
 #[derive(Clone, Deserialize, Serialize)]
-#[cfg(feature = "unstable-msc3440")]
 struct ThreadUnstableJsonRepr {
     /// The ID of the root message in the thread.
     event_id: OwnedEventId,
diff --git a/crates/ruma-common/tests/events/relations.rs b/crates/ruma-common/tests/events/relations.rs
index e65297c2..d53736af 100644
--- a/crates/ruma-common/tests/events/relations.rs
+++ b/crates/ruma-common/tests/events/relations.rs
@@ -149,7 +149,6 @@ fn replacement_deserialize() {
 }
 
 #[test]
-#[cfg(feature = "unstable-msc3440")]
 fn thread_plain_serialize() {
     use ruma_common::events::room::message::Thread;
 
@@ -172,12 +171,12 @@ fn thread_plain_serialize() {
             "msgtype": "m.text",
             "body": "<text msg>",
             "m.relates_to": {
-                "rel_type": "io.element.thread",
+                "rel_type": "m.thread",
                 "event_id": "$1598361704261elfgc",
                 "m.in_reply_to": {
                     "event_id": "$latesteventid",
                 },
-                "io.element.show_reply": true,
+                "is_falling_back": true,
             },
         })
     );
@@ -190,19 +189,18 @@ fn thread_plain_serialize() {
             "body": "<text msg>",
             "org.matrix.msc1767.text": "<text msg>",
             "m.relates_to": {
-                "rel_type": "io.element.thread",
+                "rel_type": "m.thread",
                 "event_id": "$1598361704261elfgc",
                 "m.in_reply_to": {
                     "event_id": "$latesteventid",
                 },
-                "io.element.show_reply": true,
+                "is_falling_back": true,
             },
         })
     );
 }
 
 #[test]
-#[cfg(feature = "unstable-msc3440")]
 fn thread_reply_serialize() {
     use ruma_common::events::room::message::Thread;
 
@@ -225,7 +223,7 @@ fn thread_reply_serialize() {
             "msgtype": "m.text",
             "body": "<text msg>",
             "m.relates_to": {
-                "rel_type": "io.element.thread",
+                "rel_type": "m.thread",
                 "event_id": "$1598361704261elfgc",
                 "m.in_reply_to": {
                     "event_id": "$repliedtoeventid",
@@ -242,7 +240,7 @@ fn thread_reply_serialize() {
             "body": "<text msg>",
             "org.matrix.msc1767.text": "<text msg>",
             "m.relates_to": {
-                "rel_type": "io.element.thread",
+                "rel_type": "m.thread",
                 "event_id": "$1598361704261elfgc",
                 "m.in_reply_to": {
                     "event_id": "$repliedtoeventid",
@@ -253,7 +251,6 @@ fn thread_reply_serialize() {
 }
 
 #[test]
-#[cfg(feature = "unstable-msc3440")]
 fn thread_stable_deserialize() {
     let json = json!({
         "msgtype": "m.text",
@@ -281,7 +278,6 @@ fn thread_stable_deserialize() {
 }
 
 #[test]
-#[cfg(feature = "unstable-msc3440")]
 fn thread_unstable_deserialize() {
     let json = json!({
         "msgtype": "m.text",
diff --git a/crates/ruma/Cargo.toml b/crates/ruma/Cargo.toml
index 317d8727..410076f2 100644
--- a/crates/ruma/Cargo.toml
+++ b/crates/ruma/Cargo.toml
@@ -141,7 +141,6 @@ unstable-msc2967 = ["ruma-client-api?/unstable-msc2967"]
 unstable-msc3245 = ["ruma-common/unstable-msc3245"]
 unstable-msc3246 = ["ruma-common/unstable-msc3246"]
 unstable-msc3381 = ["ruma-common/unstable-msc3381"]
-unstable-msc3440 = ["ruma-common/unstable-msc3440"]
 unstable-msc3488 = [
     "ruma-client-api?/unstable-msc3488",
     "ruma-common/unstable-msc3488",
@@ -179,7 +178,6 @@ __ci = [
     "unstable-msc3245",
     "unstable-msc3246",
     "unstable-msc3381",
-    "unstable-msc3440",
     "unstable-msc3488",
     "unstable-msc3551",
     "unstable-msc3552",