diff --git a/spec/integ/matrix-client-event-timeline.spec.ts b/spec/integ/matrix-client-event-timeline.spec.ts
index dbcb48acda7..bb4e9563431 100644
--- a/spec/integ/matrix-client-event-timeline.spec.ts
+++ b/spec/integ/matrix-client-event-timeline.spec.ts
@@ -21,11 +21,13 @@ import {
     EventStatus,
     EventTimeline,
     EventTimelineSet,
+    EventType,
     Filter,
     IEvent,
     MatrixClient,
     MatrixEvent,
     PendingEventOrdering,
+    RelationType,
     Room,
 } from "../../src/matrix";
 import { logger } from "../../src/logger";
@@ -33,6 +35,7 @@ import { encodeParams, encodeUri, QueryDict, replaceParam } from "../../src/util
 import { TestClient } from "../TestClient";
 import { FeatureSupport, Thread, THREAD_RELATION_TYPE, ThreadEvent } from "../../src/models/thread";
 import { emitPromise } from "../test-utils/test-utils";
+import { Feature, ServerSupport } from "../../src/feature";
 
 const userId = "@alice:localhost";
 const userName = "Alice";
@@ -1164,6 +1167,117 @@ describe("MatrixClient event timelines", function () {
         ]);
     });
 
+    it("should ensure thread events don't get reordered with recursive relations", async () => {
+        // Test data for a second reply to the first thread
+        const THREAD_REPLY2 = utils.mkEvent({
+            room: roomId,
+            user: userId,
+            type: "m.room.message",
+            content: {
+                "body": "thread reply 2",
+                "msgtype": "m.text",
+                "m.relates_to": {
+                    // We can't use the const here because we change server support mode for test
+                    rel_type: "io.element.thread",
+                    event_id: THREAD_ROOT.event_id,
+                },
+            },
+            event: true,
+        });
+        THREAD_REPLY2.localTimestamp += 1000;
+        const THREAD_ROOT_REACTION = utils.mkEvent({
+            event: true,
+            type: EventType.Reaction,
+            user: userId,
+            room: roomId,
+            content: {
+                "m.relates_to": {
+                    rel_type: RelationType.Annotation,
+                    event_id: THREAD_ROOT.event_id!,
+                    key: Math.random().toString(),
+                },
+            },
+        });
+        THREAD_ROOT_REACTION.localTimestamp += 2000;
+
+        // Test data for a second reply to the first thread
+        const THREAD_REPLY3 = utils.mkEvent({
+            room: roomId,
+            user: userId,
+            type: "m.room.message",
+            content: {
+                "body": "thread reply 3",
+                "msgtype": "m.text",
+                "m.relates_to": {
+                    // We can't use the const here because we change server support mode for test
+                    rel_type: "io.element.thread",
+                    event_id: THREAD_ROOT.event_id,
+                },
+            },
+            event: true,
+        });
+        THREAD_REPLY3.localTimestamp += 3000;
+
+        // Test data for the first thread, with the second reply
+        const THREAD_ROOT_UPDATED = {
+            ...THREAD_ROOT,
+            unsigned: {
+                ...THREAD_ROOT.unsigned,
+                "m.relations": {
+                    ...THREAD_ROOT.unsigned!["m.relations"],
+                    "io.element.thread": {
+                        ...THREAD_ROOT.unsigned!["m.relations"]!["io.element.thread"],
+                        count: 3,
+                        latest_event: THREAD_REPLY3.event,
+                    },
+                },
+            },
+        };
+
+        // @ts-ignore
+        client.clientOpts.threadSupport = true;
+        client.canSupport.set(Feature.RelationsRecursion, ServerSupport.Stable);
+        Thread.setServerSideSupport(FeatureSupport.Stable);
+        Thread.setServerSideListSupport(FeatureSupport.Stable);
+        Thread.setServerSideFwdPaginationSupport(FeatureSupport.Stable);
+
+        client.fetchRoomEvent = () => Promise.resolve(THREAD_ROOT_UPDATED);
+
+        await client.stopClient(); // we don't need the client to be syncing at this time
+        const room = client.getRoom(roomId)!;
+
+        const prom = emitPromise(room, ThreadEvent.Update);
+        // Assume we're seeing the reply while loading backlog
+        room.addLiveEvents([THREAD_REPLY2]);
+        httpBackend
+            .when(
+                "GET",
+                "/_matrix/client/v1/rooms/!foo%3Abar/relations/" +
+                    encodeURIComponent(THREAD_ROOT_UPDATED.event_id!) +
+                    "/" +
+                    encodeURIComponent(THREAD_RELATION_TYPE.name) +
+                    buildRelationPaginationQuery({
+                        dir: Direction.Backward,
+                        limit: 3,
+                        recurse: true,
+                    }),
+            )
+            .respond(200, {
+                chunk: [THREAD_REPLY3.event, THREAD_ROOT_REACTION, THREAD_REPLY2.event, THREAD_REPLY],
+            });
+        await flushHttp(prom);
+        // but while loading the metadata, a new reply has arrived
+        room.addLiveEvents([THREAD_REPLY3]);
+        const thread = room.getThread(THREAD_ROOT_UPDATED.event_id!)!;
+        // then the events should still be all in the right order
+        expect(thread.events.map((it) => it.getId())).toEqual([
+            THREAD_ROOT.event_id,
+            THREAD_REPLY.event_id,
+            THREAD_REPLY2.getId(),
+            THREAD_REPLY3.getId(),
+        ]);
+    });
+
     describe("paginateEventTimeline for thread list timeline", function () {
         const RANDOM_TOKEN = "7280349c7bee430f91defe2a38a0a08c";
 
@@ -1847,7 +1961,10 @@ describe("MatrixClient event timelines", function () {
                         encodeURIComponent(THREAD_ROOT.event_id!) +
                         "/" +
                         encodeURIComponent(THREAD_RELATION_TYPE.name) +
-                        buildRelationPaginationQuery({ dir: Direction.Backward, from: "start_token" }),
+                        buildRelationPaginationQuery({
+                            dir: Direction.Backward,
+                            from: "start_token",
+                        }),
                 )
                 .respond(200, function () {
                     return {
diff --git a/spec/unit/event-timeline-set.spec.ts b/spec/unit/event-timeline-set.spec.ts
index 4a624268c8a..a099aba0370 100644
--- a/spec/unit/event-timeline-set.spec.ts
+++ b/spec/unit/event-timeline-set.spec.ts
@@ -82,6 +82,7 @@ describe("EventTimelineSet", () => {
     beforeEach(() => {
         client = utils.mock(MatrixClient, "MatrixClient");
         client.reEmitter = utils.mock(ReEmitter, "ReEmitter");
+        client.canSupport = new Map();
         room = new Room(roomId, client, userA);
         eventTimelineSet = new EventTimelineSet(room);
         eventTimeline = new EventTimeline(eventTimelineSet);
diff --git a/src/@types/requests.ts b/src/@types/requests.ts
index 12f4d8eb00a..364b9f12c2a 100644
--- a/src/@types/requests.ts
+++ b/src/@types/requests.ts
@@ -186,6 +186,7 @@ export interface IRelationsRequestOpts {
     to?: string;
     limit?: number;
     dir?: Direction;
+    recurse?: boolean; // MSC3981 Relations Recursion /~https://github.com/matrix-org/matrix-spec-proposals/pull/3981
 }
 
 export interface IRelationsResponse {
diff --git a/src/client.ts b/src/client.ts
index ea53b62f28c..c545c2bbd49 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -5736,6 +5736,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             return undefined;
         }
 
+        const recurse = this.canSupport.get(Feature.RelationsRecursion) !== ServerSupport.Unsupported;
         if (Thread.hasServerSideSupport) {
             if (Thread.hasServerSideFwdPaginationSupport) {
                 if (!timelineSet.thread) {
@@ -5748,14 +5749,14 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                     thread.id,
                     THREAD_RELATION_TYPE.name,
                     null,
-                    { dir: Direction.Backward, from: res.start },
+                    { dir: Direction.Backward, from: res.start, recurse: recurse || undefined },
                 );
                 const resNewer: IRelationsResponse = await this.fetchRelations(
                     timelineSet.room.roomId,
                     thread.id,
                     THREAD_RELATION_TYPE.name,
                     null,
-                    { dir: Direction.Forward, from: res.end },
+                    { dir: Direction.Forward, from: res.end, recurse: recurse || undefined },
                 );
                 const events = [
                     // Order events from most recent to oldest (reverse-chronological).
@@ -5803,7 +5804,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                     thread.id,
                     THREAD_RELATION_TYPE.name,
                     null,
-                    { dir: Direction.Backward, from: res.start },
+                    { dir: Direction.Backward, from: res.start, recurse: recurse || undefined },
                 );
                 const eventsNewer: IEvent[] = [];
                 let nextBatch: Optional<string> = res.end;
@@ -5813,7 +5814,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                         thread.id,
                         THREAD_RELATION_TYPE.name,
                         null,
-                        { dir: Direction.Forward, from: nextBatch },
+                        { dir: Direction.Forward, from: nextBatch, recurse: recurse || undefined },
                     );
                     nextBatch = resNewer.next_batch ?? null;
                     eventsNewer.push(...resNewer.chunk);
@@ -5884,12 +5885,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             );
             event = res.chunk?.[0];
         } else if (timelineSet.thread && Thread.hasServerSideSupport) {
+            const recurse = this.canSupport.get(Feature.RelationsRecursion) !== ServerSupport.Unsupported;
             const res = await this.fetchRelations(
                 timelineSet.room.roomId,
                 timelineSet.thread.id,
                 THREAD_RELATION_TYPE.name,
                 null,
-                { dir: Direction.Backward, limit: 1 },
+                { dir: Direction.Backward, limit: 1, recurse: recurse || undefined },
             );
             event = res.chunk?.[0];
         } else {
@@ -6164,10 +6166,12 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                 throw new Error("Unknown room " + eventTimeline.getRoomId());
             }
 
+            const recurse = this.canSupport.get(Feature.RelationsRecursion) !== ServerSupport.Unsupported;
             promise = this.fetchRelations(eventTimeline.getRoomId() ?? "", thread.id, THREAD_RELATION_TYPE.name, null, {
                 dir,
                 limit: opts.limit,
                 from: token ?? undefined,
+                recurse: recurse || undefined,
             })
                 .then(async (res) => {
                     const mapper = this.getEventMapper();
@@ -7956,6 +7960,9 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         if (Thread.hasServerSideFwdPaginationSupport === FeatureSupport.Experimental) {
             params = replaceParam("dir", "org.matrix.msc3715.dir", params);
         }
+        if (this.canSupport.get(Feature.RelationsRecursion) === ServerSupport.Unstable) {
+            params = replaceParam("recurse", "org.matrix.msc3981.recurse", params);
+        }
         const queryString = utils.encodeParams(params);
 
         let templatedUrl = "/rooms/$roomId/relations/$eventId";
diff --git a/src/feature.ts b/src/feature.ts
index 9a0f1f92ad1..a557fe80705 100644
--- a/src/feature.ts
+++ b/src/feature.ts
@@ -31,6 +31,7 @@ export enum Feature {
     LoginTokenRequest = "LoginTokenRequest",
     RelationBasedRedactions = "RelationBasedRedactions",
     AccountDataDeletion = "AccountDataDeletion",
+    RelationsRecursion = "RelationsRecursion",
 }
 
 type FeatureSupportCondition = {
@@ -56,6 +57,9 @@ const featureSupportResolver: Record<string, FeatureSupportCondition> = {
     [Feature.AccountDataDeletion]: {
         unstablePrefixes: ["org.matrix.msc3391"],
     },
+    [Feature.RelationsRecursion]: {
+        unstablePrefixes: ["org.matrix.msc3981"],
+    },
 };
 
 export async function buildFeatureSupportMap(versions: IServerVersions): Promise<Map<Feature, ServerSupport>> {
diff --git a/src/models/thread.ts b/src/models/thread.ts
index 9a4ead33bc9..c31499b2b34 100644
--- a/src/models/thread.ts
+++ b/src/models/thread.ts
@@ -28,6 +28,7 @@ import { ServerControlledNamespacedValue } from "../NamespacedValue";
 import { logger } from "../logger";
 import { ReadReceipt } from "./read-receipt";
 import { CachedReceiptStructure, ReceiptType } from "../@types/read_receipts";
+import { Feature, ServerSupport } from "../feature";
 
 export enum ThreadEvent {
     New = "Thread.new",
@@ -458,25 +459,28 @@ export class Thread extends ReadReceipt<EmittedEvents, EventHandlerMap> {
 
     // XXX: Workaround for /~https://github.com/matrix-org/matrix-spec-proposals/pull/2676/files#r827240084
     private async fetchEditsWhereNeeded(...events: MatrixEvent[]): Promise<unknown> {
-        return Promise.all(
-            events
-                .filter((e) => e.isEncrypted())
-                .map((event: MatrixEvent) => {
-                    if (event.isRelation()) return; // skip - relations don't get edits
-                    return this.client
-                        .relations(this.roomId, event.getId()!, RelationType.Replace, event.getType(), {
-                            limit: 1,
-                        })
-                        .then((relations) => {
-                            if (relations.events.length) {
-                                event.makeReplaced(relations.events[0]);
-                            }
-                        })
-                        .catch((e) => {
-                            logger.error("Failed to load edits for encrypted thread event", e);
-                        });
-                }),
-        );
+        const recursionSupport = this.client.canSupport.get(Feature.RelationsRecursion) ?? ServerSupport.Unsupported;
+        if (recursionSupport !== ServerSupport.Unsupported) {
+            return Promise.all(
+                events
+                    .filter((e) => e.isEncrypted())
+                    .map((event: MatrixEvent) => {
+                        if (event.isRelation()) return; // skip - relations don't get edits
+                        return this.client
+                            .relations(this.roomId, event.getId()!, RelationType.Replace, event.getType(), {
+                                limit: 1,
+                            })
+                            .then((relations) => {
+                                if (relations.events.length) {
+                                    event.makeReplaced(relations.events[0]);
+                                }
+                            })
+                            .catch((e) => {
+                                logger.error("Failed to load edits for encrypted thread event", e);
+                            });
+                    }),
+            );
+        }
     }
 
     public setEventMetadata(event: Optional<MatrixEvent>): void {