diff --git a/.babelrc b/.babelrc
deleted file mode 100644
index 6e6720bbf11..00000000000
--- a/.babelrc
+++ /dev/null
@@ -1,22 +0,0 @@
-{
-    "sourceMaps": true,
-    "presets": [
-        [
-            "@babel/preset-env",
-            {
-                "targets": {
-                    "node": 10
-                },
-                "modules": "commonjs"
-            }
-        ],
-        "@babel/preset-typescript"
-    ],
-    "plugins": [
-        "@babel/plugin-proposal-numeric-separator",
-        "@babel/plugin-proposal-class-properties",
-        "@babel/plugin-proposal-object-rest-spread",
-        "@babel/plugin-syntax-dynamic-import",
-        "@babel/plugin-transform-runtime"
-    ]
-}
diff --git a/.github/workflows/notify-downstream.yaml b/.github/workflows/notify-downstream.yaml
index a1c4a28a5ce..8de5da70dcd 100644
--- a/.github/workflows/notify-downstream.yaml
+++ b/.github/workflows/notify-downstream.yaml
@@ -12,7 +12,7 @@ jobs:
             fail-fast: false
             matrix:
                 include:
-                    - repo: vector-im/element-web
+                    - repo: element-hq/element-web
                       event: element-web-notify
                     - repo: matrix-org/matrix-react-sdk
                       event: upstream-sdk-notify
diff --git a/.github/workflows/triage-labelled.yml b/.github/workflows/triage-labelled.yml
index cb013753c56..e464e5b7268 100644
--- a/.github/workflows/triage-labelled.yml
+++ b/.github/workflows/triage-labelled.yml
@@ -6,6 +6,6 @@ on:
 
 jobs:
     call-triage-labelled:
-        uses: vector-im/element-web/.github/workflows/triage-labelled.yml@develop
+        uses: element-hq/element-web/.github/workflows/triage-labelled.yml@develop
         secrets:
             ELEMENT_BOT_TOKEN: ${{ secrets.ELEMENT_BOT_TOKEN }}
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a75f7cff4fa..9c190ae9c67 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,33 @@
+Changes in [33.0.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v33.0.0) (2024-06-04)
+==================================================================================================
+## 🚨 BREAKING CHANGES
+
+* Remove more deprecated methods, fields, and exports ([#4217](https://github.com/matrix-org/matrix-js-sdk/pull/4217)). Contributed by @t3chguy.
+* Remove deprecated methods and fields ([#4201](https://github.com/matrix-org/matrix-js-sdk/pull/4201)). Contributed by @t3chguy.
+
+## 🦖 Deprecations
+
+* Remove more deprecated methods, fields, and exports ([#4217](https://github.com/matrix-org/matrix-js-sdk/pull/4217)). Contributed by @t3chguy.
+* Remove deprecated methods and fields ([#4201](https://github.com/matrix-org/matrix-js-sdk/pull/4201)). Contributed by @t3chguy.
+
+## ✨ Features
+
+* `initRustCrypto`: allow app to pass in the store key directly ([#4210](https://github.com/matrix-org/matrix-js-sdk/pull/4210)). Contributed by @richvdh.
+* Preserve ESM for async imports to work correctly ([#4187](https://github.com/matrix-org/matrix-js-sdk/pull/4187)). Contributed by @ms-dosx86.
+
+## 🐛 Bug Fixes
+
+* Don't run migration for Rust crypto if the legacy store is empty ([#4218](https://github.com/matrix-org/matrix-js-sdk/pull/4218)). Contributed by @andybalaam.
+* Bump matrix-sdk-crypto-wasm to 5.0.0 ([#4216](https://github.com/matrix-org/matrix-js-sdk/pull/4216)). Contributed by @richvdh.
+* Wire up verification cancel \& mismatch for rust crypto ([#4202](https://github.com/matrix-org/matrix-js-sdk/pull/4202)). Contributed by @t3chguy.
+* Only pass id\_server if we had one to begin with ([#4200](https://github.com/matrix-org/matrix-js-sdk/pull/4200)). Contributed by @t3chguy.
+
+
+Changes in [32.4.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v32.4.0) (2024-05-22)
+==================================================================================================
+* No changes
+
+
 Changes in [32.3.0](https://github.com/matrix-org/matrix-js-sdk/releases/tag/v32.3.0) (2024-05-21)
 ==================================================================================================
 ## ✨ Features
diff --git a/babel.config.js b/babel.config.js
new file mode 100644
index 00000000000..6b39ec8271b
--- /dev/null
+++ b/babel.config.js
@@ -0,0 +1,26 @@
+module.exports = {
+    sourceMaps: true,
+    presets: [
+        [
+            "@babel/preset-env",
+            {
+                targets: {
+                    esmodules: true,
+                },
+                // We want to output ES modules for the final build (mostly to ensure that
+                // async imports work correctly). However, jest doesn't support ES modules very
+                // well yet (see https://github.com/jestjs/jest/issues/9430), so we use commonjs
+                // when testing.
+                modules: process.env.NODE_ENV === "test" ? "commonjs" : false,
+            },
+        ],
+        "@babel/preset-typescript",
+    ],
+    plugins: [
+        "@babel/plugin-proposal-numeric-separator",
+        "@babel/plugin-proposal-class-properties",
+        "@babel/plugin-proposal-object-rest-spread",
+        "@babel/plugin-syntax-dynamic-import",
+        "@babel/plugin-transform-runtime",
+    ],
+};
diff --git a/package.json b/package.json
index 24d180a625b..9011449fb29 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
     "name": "matrix-js-sdk",
-    "version": "32.3.0",
+    "version": "33.0.0",
     "description": "Matrix Client-Server SDK for Javascript",
     "engines": {
         "node": ">=18.0.0"
@@ -31,8 +31,8 @@
     "keywords": [
         "matrix-org"
     ],
-    "main": "./src/index.ts",
-    "browser": "./src/browser-index.ts",
+    "main": "./lib/index.js",
+    "browser": "./lib/browser-index.js",
     "matrix_src_main": "./src/index.ts",
     "matrix_src_browser": "./src/browser-index.ts",
     "matrix_lib_main": "./lib/index.js",
@@ -53,7 +53,7 @@
     ],
     "dependencies": {
         "@babel/runtime": "^7.12.5",
-        "@matrix-org/matrix-sdk-crypto-wasm": "^4.9.0",
+        "@matrix-org/matrix-sdk-crypto-wasm": "^5.0.0",
         "another-json": "^0.2.0",
         "bs58": "^5.0.0",
         "content-type": "^1.0.4",
@@ -132,5 +132,6 @@
         "outputDirectory": "coverage",
         "outputName": "jest-sonar-report.xml",
         "relativePaths": true
-    }
+    },
+    "typings": "./lib/index.d.ts"
 }
diff --git a/spec/integ/crypto/megolm-backup.spec.ts b/spec/integ/crypto/megolm-backup.spec.ts
index 66f7892daa5..eee0eafebc2 100644
--- a/spec/integ/crypto/megolm-backup.spec.ts
+++ b/spec/integ/crypto/megolm-backup.spec.ts
@@ -21,7 +21,7 @@ import { Mocked } from "jest-mock";
 
 import {
     createClient,
-    CryptoApi,
+    Crypto,
     CryptoEvent,
     ICreateClientOpts,
     IEvent,
@@ -310,7 +310,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("megolm-keys backup (%s)", (backe
     });
 
     describe("recover from backup", () => {
-        let aliceCrypto: CryptoApi;
+        let aliceCrypto: Crypto.CryptoApi;
 
         beforeEach(async () => {
             fetchMock.get("path:/_matrix/client/v3/room_keys/version", testData.SIGNED_BACKUP_DATA);
diff --git a/spec/integ/crypto/rust-crypto.spec.ts b/spec/integ/crypto/rust-crypto.spec.ts
index 311410febbe..a1b7a7545ed 100644
--- a/spec/integ/crypto/rust-crypto.spec.ts
+++ b/spec/integ/crypto/rust-crypto.spec.ts
@@ -23,6 +23,7 @@ import { populateStore } from "../../test-utils/test_indexeddb_cryptostore_dump"
 import { MSK_NOT_CACHED_DATASET } from "../../test-utils/test_indexeddb_cryptostore_dump/no_cached_msk_dump";
 import { IDENTITY_NOT_TRUSTED_DATASET } from "../../test-utils/test_indexeddb_cryptostore_dump/unverified";
 import { FULL_ACCOUNT_DATASET } from "../../test-utils/test_indexeddb_cryptostore_dump/full_account";
+import { EMPTY_ACCOUNT_DATASET } from "../../test-utils/test_indexeddb_cryptostore_dump/empty_account";
 
 jest.setTimeout(15000);
 
@@ -85,6 +86,44 @@ describe("MatrixClient.initRustCrypto", () => {
         );
     });
 
+    it("should create the meta db if given a storageKey", async () => {
+        const matrixClient = createClient({
+            baseUrl: "http://test.server",
+            userId: "@alice:localhost",
+            deviceId: "aliceDevice",
+        });
+
+        // No databases.
+        expect(await indexedDB.databases()).toHaveLength(0);
+
+        await matrixClient.initRustCrypto({ storageKey: new Uint8Array(32) });
+
+        // should have two indexed dbs now
+        const databaseNames = (await indexedDB.databases()).map((db) => db.name);
+        expect(databaseNames).toEqual(
+            expect.arrayContaining(["matrix-js-sdk::matrix-sdk-crypto", "matrix-js-sdk::matrix-sdk-crypto-meta"]),
+        );
+    });
+
+    it("should create the meta db if given a storagePassword", async () => {
+        const matrixClient = createClient({
+            baseUrl: "http://test.server",
+            userId: "@alice:localhost",
+            deviceId: "aliceDevice",
+        });
+
+        // No databases.
+        expect(await indexedDB.databases()).toHaveLength(0);
+
+        await matrixClient.initRustCrypto({ storagePassword: "the cow is on the moon" });
+
+        // should have two indexed dbs now
+        const databaseNames = (await indexedDB.databases()).map((db) => db.name);
+        expect(databaseNames).toEqual(
+            expect.arrayContaining(["matrix-js-sdk::matrix-sdk-crypto", "matrix-js-sdk::matrix-sdk-crypto-meta"]),
+        );
+    });
+
     it("should ignore a second call", async () => {
         const matrixClient = createClient({
             baseUrl: "http://test.server",
@@ -266,6 +305,38 @@ describe("MatrixClient.initRustCrypto", () => {
             });
         });
 
+        it("should not migrate if account data is missing", async () => {
+            // See https://github.com/element-hq/element-web/issues/27447
+
+            // Given we have an almost-empty legacy account in the database
+            fetchMock.get("path:/_matrix/client/v3/room_keys/version", {
+                status: 404,
+                body: { errcode: "M_NOT_FOUND", error: "No backup found" },
+            });
+            fetchMock.post("path:/_matrix/client/v3/keys/query", EMPTY_ACCOUNT_DATASET.keyQueryResponse);
+
+            const testStoreName = "test-store";
+            await populateStore(testStoreName, EMPTY_ACCOUNT_DATASET.dumpPath);
+            const cryptoStore = new IndexedDBCryptoStore(indexedDB, testStoreName);
+
+            const matrixClient = createClient({
+                baseUrl: "http://test.server",
+                userId: EMPTY_ACCOUNT_DATASET.userId,
+                deviceId: EMPTY_ACCOUNT_DATASET.deviceId,
+                cryptoStore,
+                pickleKey: EMPTY_ACCOUNT_DATASET.pickleKey,
+            });
+
+            // When we start Rust crypto, potentially triggering an upgrade
+            const progressListener = jest.fn();
+            matrixClient.addListener(CryptoEvent.LegacyCryptoStoreMigrationProgress, progressListener);
+
+            await matrixClient.initRustCrypto();
+
+            // Then no error occurs, and no upgrade happens
+            expect(progressListener.mock.calls.length).toBe(0);
+        }, 60000);
+
         describe("Legacy trust migration", () => {
             async function populateAndStartLegacyCryptoStore(dumpPath: string): Promise<IndexedDBCryptoStore> {
                 const testStoreName = "test-store";
diff --git a/spec/integ/matrix-client-methods.spec.ts b/spec/integ/matrix-client-methods.spec.ts
index a66d41b3dbd..06986652d48 100644
--- a/spec/integ/matrix-client-methods.spec.ts
+++ b/spec/integ/matrix-client-methods.spec.ts
@@ -1825,7 +1825,6 @@ function withThreadId(event: MatrixEvent, newThreadId: string): MatrixEvent {
 
 const buildEventMessageInThread = (root: MatrixEvent) =>
     new MatrixEvent({
-        age: 80098509,
         content: {
             "algorithm": "m.megolm.v1.aes-sha2",
             "ciphertext": "ENCRYPTEDSTUFF",
@@ -1846,12 +1845,10 @@ const buildEventMessageInThread = (root: MatrixEvent) =>
         sender: "@andybalaam-test1:matrix.org",
         type: "m.room.encrypted",
         unsigned: { age: 80098509 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventPollResponseReference = () =>
     new MatrixEvent({
-        age: 80098509,
         content: {
             "algorithm": "m.megolm.v1.aes-sha2",
             "ciphertext": "ENCRYPTEDSTUFF",
@@ -1869,7 +1866,6 @@ const buildEventPollResponseReference = () =>
         sender: "@andybalaam-test1:matrix.org",
         type: "m.room.encrypted",
         unsigned: { age: 80106237 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventReaction = (event: MatrixEvent) =>
@@ -1909,7 +1905,6 @@ const buildEventRedaction = (event: MatrixEvent) =>
 
 const buildEventPollStartThreadRoot = () =>
     new MatrixEvent({
-        age: 80108647,
         content: {
             algorithm: "m.megolm.v1.aes-sha2",
             ciphertext: "ENCRYPTEDSTUFF",
@@ -1923,12 +1918,10 @@ const buildEventPollStartThreadRoot = () =>
         sender: "@andybalaam-test1:matrix.org",
         type: "m.room.encrypted",
         unsigned: { age: 80108647 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventReply = (target: MatrixEvent) =>
     new MatrixEvent({
-        age: 80098509,
         content: {
             "algorithm": "m.megolm.v1.aes-sha2",
             "ciphertext": "ENCRYPTEDSTUFF",
@@ -1947,12 +1940,10 @@ const buildEventReply = (target: MatrixEvent) =>
         sender: "@andybalaam-test1:matrix.org",
         type: "m.room.encrypted",
         unsigned: { age: 80098509 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventRoomName = () =>
     new MatrixEvent({
-        age: 80123249,
         content: {
             name: "1 poll, 1 vote, 1 thread",
         },
@@ -1963,12 +1954,10 @@ const buildEventRoomName = () =>
         state_key: "",
         type: "m.room.name",
         unsigned: { age: 80123249 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventEncryption = () =>
     new MatrixEvent({
-        age: 80123383,
         content: {
             algorithm: "m.megolm.v1.aes-sha2",
         },
@@ -1979,12 +1968,10 @@ const buildEventEncryption = () =>
         state_key: "",
         type: "m.room.encryption",
         unsigned: { age: 80123383 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventGuestAccess = () =>
     new MatrixEvent({
-        age: 80123473,
         content: {
             guest_access: "can_join",
         },
@@ -1995,12 +1982,10 @@ const buildEventGuestAccess = () =>
         state_key: "",
         type: "m.room.guest_access",
         unsigned: { age: 80123473 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventHistoryVisibility = () =>
     new MatrixEvent({
-        age: 80123556,
         content: {
             history_visibility: "shared",
         },
@@ -2011,12 +1996,10 @@ const buildEventHistoryVisibility = () =>
         state_key: "",
         type: "m.room.history_visibility",
         unsigned: { age: 80123556 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventJoinRules = () =>
     new MatrixEvent({
-        age: 80123696,
         content: {
             join_rule: KnownMembership.Invite,
         },
@@ -2027,12 +2010,10 @@ const buildEventJoinRules = () =>
         state_key: "",
         type: "m.room.join_rules",
         unsigned: { age: 80123696 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventPowerLevels = () =>
     new MatrixEvent({
-        age: 80124105,
         content: {
             ban: 50,
             events: {
@@ -2063,12 +2044,10 @@ const buildEventPowerLevels = () =>
         state_key: "",
         type: "m.room.power_levels",
         unsigned: { age: 80124105 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventMember = () =>
     new MatrixEvent({
-        age: 80125279,
         content: {
             avatar_url: "mxc://matrix.org/aNtbVcFfwotudypZcHsIcPOc",
             displayname: "andybalaam-test1",
@@ -2081,12 +2060,10 @@ const buildEventMember = () =>
         state_key: "@andybalaam-test1:matrix.org",
         type: "m.room.member",
         unsigned: { age: 80125279 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 const buildEventCreate = () =>
     new MatrixEvent({
-        age: 80126105,
         content: {
             room_version: "6",
         },
@@ -2097,7 +2074,6 @@ const buildEventCreate = () =>
         state_key: "",
         type: "m.room.create",
         unsigned: { age: 80126105 },
-        user_id: "@andybalaam-test1:matrix.org",
     });
 
 function assertObjectContains(obj: Record<string, any>, expected: any): void {
diff --git a/spec/integ/matrix-client-room-timeline.spec.ts b/spec/integ/matrix-client-room-timeline.spec.ts
index a5d4c220a95..1d0ed86e0d3 100644
--- a/spec/integ/matrix-client-room-timeline.spec.ts
+++ b/spec/integ/matrix-client-room-timeline.spec.ts
@@ -333,7 +333,7 @@ describe("MatrixClient room timelines", function () {
                 name: userName,
                 url: "mxc://some/url",
             });
-            oldMshipEvent.prev_content = {
+            oldMshipEvent.unsigned!.prev_content = {
                 displayname: "Old Alice",
                 avatar_url: undefined,
                 membership: KnownMembership.Join,
diff --git a/spec/test-utils/test-utils.ts b/spec/test-utils/test-utils.ts
index 965a6a08806..a6cc6445565 100644
--- a/spec/test-utils/test-utils.ts
+++ b/spec/test-utils/test-utils.ts
@@ -173,8 +173,10 @@ export function mkEvent(opts: IEventOpts & { event?: boolean }, client?: MatrixC
         room_id: opts.room,
         sender: opts.sender || opts.user, // opts.user for backwards-compat
         content: opts.content,
-        prev_content: opts.prev_content,
-        unsigned: opts.unsigned || {},
+        unsigned: {
+            ...opts.unsigned,
+            prev_content: opts.prev_content,
+        },
         event_id: "$" + testEventIndex++ + "-" + Math.random() + "-" + Math.random(),
         txn_id: "~" + Math.random(),
         redacts: opts.redacts,
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/README.md b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/README.md
new file mode 100644
index 00000000000..df3ab87e55c
--- /dev/null
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/README.md
@@ -0,0 +1,10 @@
+## Dump of an empty libolm indexeddb cryptostore to test skipping migration
+
+A dump of an account which is almost completely empty, and totally unsuitable
+for use as a real account.
+
+This dump was manually created by copying and editing full_account.
+
+Created to test
+["Unable to restore session" error due due to half-initialised legacy indexeddb crypto store #27447](https://github.com/element-hq/element-web/issues/27447).
+We should not launch the Rust migration code when we find a DB in this state.
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/dump.json b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/dump.json
new file mode 100644
index 00000000000..10227c8bc43
--- /dev/null
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/dump.json
@@ -0,0 +1,14 @@
+{
+    "account": [],
+    "device_data": [],
+    "inbound_group_sessions": [],
+    "inbound_group_sessions_withheld": [],
+    "notified_error_devices": [],
+    "outgoingRoomKeyRequests": [],
+    "parked_shared_history": [],
+    "rooms": [],
+    "session_problems": [],
+    "sessions": [],
+    "sessions_needing_backup": [],
+    "shared_history_inbound_group_sessions": []
+}
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/index.ts b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/index.ts
new file mode 100644
index 00000000000..db196e99424
--- /dev/null
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/index.ts
@@ -0,0 +1,35 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import { DumpDataSetInfo } from "../index";
+
+/**
+ * A key query response containing the current keys of the tested user.
+ * To be used during tests with fetchmock.
+ */
+const KEYS_QUERY_RESPONSE = { device_keys: { "@emptyuser:example.com": {} } };
+
+/**
+ * A dataset containing the information for the tested user.
+ * To be used during tests.
+ */
+export const EMPTY_ACCOUNT_DATASET: DumpDataSetInfo = {
+    userId: "@emptyuser:example.com",
+    deviceId: "EMPTYDEVIC",
+    pickleKey: "+/bcdefghijklmnopqrstu1/zyxvutsrqponmlkjih2",
+    keyQueryResponse: KEYS_QUERY_RESPONSE,
+    dumpPath: "spec/test-utils/test_indexeddb_cryptostore_dump/empty_account/dump.json",
+};
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/full_account/index.ts b/spec/test-utils/test_indexeddb_cryptostore_dump/full_account/index.ts
index 96aa258401d..3ea92d6b210 100644
--- a/spec/test-utils/test_indexeddb_cryptostore_dump/full_account/index.ts
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/full_account/index.ts
@@ -1,3 +1,19 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
 import { DumpDataSetInfo } from "../index";
 
 /**
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/no_cached_msk_dump/index.ts b/spec/test-utils/test_indexeddb_cryptostore_dump/no_cached_msk_dump/index.ts
index bc4c8449fed..3d2a380d433 100644
--- a/spec/test-utils/test_indexeddb_cryptostore_dump/no_cached_msk_dump/index.ts
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/no_cached_msk_dump/index.ts
@@ -1,3 +1,19 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
 import { KeyBackupInfo } from "../../../../src/crypto-api/keybackup";
 import { DumpDataSetInfo } from "../index";
 
diff --git a/spec/test-utils/test_indexeddb_cryptostore_dump/unverified/index.ts b/spec/test-utils/test_indexeddb_cryptostore_dump/unverified/index.ts
index b89a0f3caef..4499180b6da 100644
--- a/spec/test-utils/test_indexeddb_cryptostore_dump/unverified/index.ts
+++ b/spec/test-utils/test_indexeddb_cryptostore_dump/unverified/index.ts
@@ -1,3 +1,19 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
 import { DumpDataSetInfo } from "../index";
 
 /**
diff --git a/spec/unit/autodiscovery.spec.ts b/spec/unit/autodiscovery.spec.ts
index ceed8be1f57..e4c7c98b293 100644
--- a/spec/unit/autodiscovery.spec.ts
+++ b/spec/unit/autodiscovery.spec.ts
@@ -857,7 +857,7 @@ describe("AutoDiscovery", function () {
                 const expected = {
                     "m.homeserver": {
                         state: AutoDiscoveryAction.FAIL_ERROR,
-                        error: AutoDiscovery.ERROR_HOMESERVER_TOO_OLD,
+                        error: AutoDiscovery.ERROR_UNSUPPORTED_HOMESERVER_SPEC_VERSION,
                         base_url: "https://example.org",
                     },
                     "m.identity_server": {
diff --git a/spec/unit/event-timeline-set.spec.ts b/spec/unit/event-timeline-set.spec.ts
index a817127569c..c89ddc4606e 100644
--- a/spec/unit/event-timeline-set.spec.ts
+++ b/spec/unit/event-timeline-set.spec.ts
@@ -136,11 +136,6 @@ describe("EventTimelineSet", () => {
             expect(eventsInLiveTimeline.length).toStrictEqual(1);
             expect(eventsInLiveTimeline[0]).toStrictEqual(duplicateMessageEvent);
         });
-
-        it("Make sure legacy overload passing options directly as parameters still works", () => {
-            expect(() => eventTimelineSet.addLiveEvent(messageEvent, DuplicateStrategy.Replace, false)).not.toThrow();
-            expect(() => eventTimelineSet.addLiveEvent(messageEvent, DuplicateStrategy.Ignore, true)).not.toThrow();
-        });
     });
 
     describe("addEventToTimeline", () => {
diff --git a/spec/unit/matrix-client.spec.ts b/spec/unit/matrix-client.spec.ts
index b83e841fcf6..fa9cd776902 100644
--- a/spec/unit/matrix-client.spec.ts
+++ b/spec/unit/matrix-client.spec.ts
@@ -1560,7 +1560,6 @@ describe("MatrixClient", function () {
                     },
                 },
                 event_id: "$ev1",
-                user_id: "@alice:matrix.org",
             });
 
             expect(rootEvent.isThreadRoot).toBe(true);
diff --git a/spec/unit/room.spec.ts b/spec/unit/room.spec.ts
index 6ca454ef82a..eb90b8bdfa0 100644
--- a/spec/unit/room.spec.ts
+++ b/spec/unit/room.spec.ts
@@ -22,7 +22,7 @@ import { mocked } from "jest-mock";
 import { M_POLL_KIND_DISCLOSED, M_POLL_RESPONSE, M_POLL_START, Optional, PollStartEvent } from "matrix-events-sdk";
 
 import * as utils from "../test-utils/test-utils";
-import { emitPromise } from "../test-utils/test-utils";
+import { emitPromise, IMessageOpts } from "../test-utils/test-utils";
 import {
     Direction,
     DuplicateStrategy,
@@ -54,7 +54,6 @@ import { Crypto } from "../../src/crypto";
 import * as threadUtils from "../test-utils/thread";
 import { getMockClientWithEventEmitter, mockClientMethodsUser } from "../test-utils/client";
 import { logger } from "../../src/logger";
-import { IMessageOpts } from "../test-utils/test-utils";
 import { flushPromises } from "../test-utils/flushPromises";
 import { KnownMembership } from "../../src/@types/membership";
 
@@ -339,24 +338,6 @@ describe("Room", function () {
             }),
         ];
 
-        it("Make sure legacy overload passing options directly as parameters still works", async () => {
-            await expect(room.addLiveEvents(events, DuplicateStrategy.Replace, false)).resolves.not.toThrow();
-            await expect(room.addLiveEvents(events, DuplicateStrategy.Ignore, true)).resolves.not.toThrow();
-            await expect(
-                // @ts-ignore
-                room.addLiveEvents(events, "shouldfailbecauseinvalidduplicatestrategy", false),
-            ).rejects.toThrow();
-        });
-
-        it("should throw if duplicateStrategy isn't 'replace' or 'ignore'", async function () {
-            return expect(
-                // @ts-ignore
-                room.addLiveEvents(events, {
-                    duplicateStrategy: "foo",
-                }),
-            ).rejects.toThrow();
-        });
-
         it("should replace a timeline event if dupe strategy is 'replace'", async function () {
             // make a duplicate
             const dupe = utils.mkMessage({
@@ -387,7 +368,7 @@ describe("Room", function () {
             expect(room.timeline[0]).toEqual(events[0]);
             // @ts-ignore
             await room.addLiveEvents([dupe], {
-                duplicateStrategy: "ignore",
+                duplicateStrategy: DuplicateStrategy.Ignore,
             });
             expect(room.timeline[0]).toEqual(events[0]);
         });
diff --git a/spec/unit/rust-crypto/rust-crypto.spec.ts b/spec/unit/rust-crypto/rust-crypto.spec.ts
index 1a1ff5525fc..57c1066d593 100644
--- a/spec/unit/rust-crypto/rust-crypto.spec.ts
+++ b/spec/unit/rust-crypto/rust-crypto.spec.ts
@@ -104,7 +104,7 @@ describe("initRustCrypto", () => {
         } as unknown as Mocked<OlmMachine>;
     }
 
-    it("passes through the store params", async () => {
+    it("passes through the store params (passphrase)", async () => {
         const mockStore = { free: jest.fn() } as unknown as StoreHandle;
         jest.spyOn(StoreHandle, "open").mockResolvedValue(mockStore);
 
@@ -126,7 +126,30 @@ describe("initRustCrypto", () => {
         expect(OlmMachine.initFromStore).toHaveBeenCalledWith(expect.anything(), expect.anything(), mockStore);
     });
 
-    it("suppresses the storePassphrase if storePrefix is unset", async () => {
+    it("passes through the store params (key)", async () => {
+        const mockStore = { free: jest.fn() } as unknown as StoreHandle;
+        jest.spyOn(StoreHandle, "openWithKey").mockResolvedValue(mockStore);
+
+        const testOlmMachine = makeTestOlmMachine();
+        jest.spyOn(OlmMachine, "initFromStore").mockResolvedValue(testOlmMachine);
+
+        const storeKey = new Uint8Array(32);
+        await initRustCrypto({
+            logger,
+            http: {} as MatrixClient["http"],
+            userId: TEST_USER,
+            deviceId: TEST_DEVICE_ID,
+            secretStorage: {} as ServerSideSecretStorage,
+            cryptoCallbacks: {} as CryptoCallbacks,
+            storePrefix: "storePrefix",
+            storeKey: storeKey,
+        });
+
+        expect(StoreHandle.openWithKey).toHaveBeenCalledWith("storePrefix", storeKey);
+        expect(OlmMachine.initFromStore).toHaveBeenCalledWith(expect.anything(), expect.anything(), mockStore);
+    });
+
+    it("suppresses the storePassphrase and storeKey if storePrefix is unset", async () => {
         const mockStore = { free: jest.fn() } as unknown as StoreHandle;
         jest.spyOn(StoreHandle, "open").mockResolvedValue(mockStore);
 
@@ -141,10 +164,11 @@ describe("initRustCrypto", () => {
             secretStorage: {} as ServerSideSecretStorage,
             cryptoCallbacks: {} as CryptoCallbacks,
             storePrefix: null,
+            storeKey: new Uint8Array(),
             storePassphrase: "storePassphrase",
         });
 
-        expect(StoreHandle.open).toHaveBeenCalledWith(undefined, undefined);
+        expect(StoreHandle.open).toHaveBeenCalledWith();
         expect(OlmMachine.initFromStore).toHaveBeenCalledWith(expect.anything(), expect.anything(), mockStore);
     });
 
@@ -1395,14 +1419,15 @@ describe("RustCrypto", () => {
             const rustCrypto = await makeTestRustCrypto();
             const olmMachine: OlmMachine = rustCrypto["olmMachine"];
 
+            const backupVersion = testData.SIGNED_BACKUP_DATA.version!;
             await olmMachine.enableBackupV1(
                 (testData.SIGNED_BACKUP_DATA.auth_data as Curve25519AuthData).public_key,
-                testData.SIGNED_BACKUP_DATA.version!,
+                backupVersion,
             );
 
             // we import two keys: one "from backup", and one "from export"
             const [backedUpRoomKey, exportedRoomKey] = testData.MEGOLM_SESSION_DATA_ARRAY;
-            await rustCrypto.importBackedUpRoomKeys([backedUpRoomKey]);
+            await rustCrypto.importBackedUpRoomKeys([backedUpRoomKey], backupVersion);
             await rustCrypto.importRoomKeys([exportedRoomKey]);
 
             // we ask for the keys that should be backed up
@@ -1437,16 +1462,17 @@ describe("RustCrypto", () => {
             const rustCrypto = await makeTestRustCrypto();
             const olmMachine: OlmMachine = rustCrypto["olmMachine"];
 
+            const backupVersion = testData.SIGNED_BACKUP_DATA.version!;
             await olmMachine.enableBackupV1(
                 (testData.SIGNED_BACKUP_DATA.auth_data as Curve25519AuthData).public_key,
-                testData.SIGNED_BACKUP_DATA.version!,
+                backupVersion,
             );
 
             const backup = Array.from(testData.MEGOLM_SESSION_DATA_ARRAY);
             // in addition to correct keys, we restore an invalid key
             backup.push({ room_id: "!roomid", session_id: "sessionid" } as IMegolmSessionData);
             const progressCallback = jest.fn();
-            await rustCrypto.importBackedUpRoomKeys(backup, { progressCallback });
+            await rustCrypto.importBackedUpRoomKeys(backup, backupVersion, { progressCallback });
             expect(progressCallback).toHaveBeenCalledWith({
                 total: 3,
                 successes: 0,
diff --git a/src/@types/registration.ts b/src/@types/registration.ts
index 90fc098e482..7bfb99f7d40 100644
--- a/src/@types/registration.ts
+++ b/src/@types/registration.ts
@@ -52,21 +52,13 @@ export interface RegisterRequest {
      */
     initial_device_display_name?: string;
     /**
-     * @deprecated missing in the spec
+     * Guest users can also upgrade their account by going through the ordinary register flow,
+     * but specifying the additional POST parameter guest_access_token containing the guest’s access token.
+     * They are also required to specify the username parameter to the value of the local part of their username,
+     * which is otherwise optional.
+     * @see https://spec.matrix.org/v1.10/client-server-api/#guest-access
      */
     guest_access_token?: string;
-    /**
-     * @deprecated missing in the spec
-     */
-    x_show_msisdn?: boolean;
-    /**
-     * @deprecated missing in the spec
-     */
-    bind_msisdn?: boolean;
-    /**
-     * @deprecated missing in the spec
-     */
-    bind_email?: boolean;
 }
 
 /**
diff --git a/src/autodiscovery.ts b/src/autodiscovery.ts
index 29dac54bdb7..8f4f196682c 100644
--- a/src/autodiscovery.ts
+++ b/src/autodiscovery.ts
@@ -43,8 +43,6 @@ export enum AutoDiscoveryError {
     InvalidJson = "Invalid JSON",
     UnsupportedHomeserverSpecVersion = "The homeserver does not meet the version requirements",
 
-    /** @deprecated Replaced by `UnsupportedHomeserverSpecVersion` */
-    HomeserverTooOld = UnsupportedHomeserverSpecVersion,
     // TODO: Implement when Sydent supports the `/versions` endpoint - https://github.com/matrix-org/sydent/issues/424
     //IdentityServerTooOld = "The identity server does not meet the minimum version requirements",
 }
@@ -91,9 +89,6 @@ export class AutoDiscovery {
     public static readonly ERROR_UNSUPPORTED_HOMESERVER_SPEC_VERSION =
         AutoDiscoveryError.UnsupportedHomeserverSpecVersion;
 
-    /** @deprecated Replaced by ERROR_UNSUPPORTED_HOMESERVER_SPEC_VERSION */
-    public static readonly ERROR_HOMESERVER_TOO_OLD = AutoDiscovery.ERROR_UNSUPPORTED_HOMESERVER_SPEC_VERSION;
-
     public static readonly ALL_ERRORS = Object.keys(AutoDiscoveryError) as AutoDiscoveryError[];
 
     /**
diff --git a/src/client.ts b/src/client.ts
index 27485d076f8..72e28f52916 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -357,14 +357,14 @@ export interface ICreateClientOpts {
     deviceToImport?: IExportedDevice;
 
     /**
-     * Encryption key used for encrypting sensitive data (such as e2ee keys) in storage.
+     * Encryption key used for encrypting sensitive data (such as e2ee keys) in {@link ICreateClientOpts#cryptoStore}.
      *
      * This must be set to the same value every time the client is initialised for the same device.
      *
-     * If unset, either a hardcoded key or no encryption at all is used, depending on the Crypto implementation.
-     *
-     * No particular requirement is placed on the key data (it is fed into an HKDF to generate the actual encryption
-     * keys).
+     * This is only used for the legacy crypto implementation (as used by {@link MatrixClient#initCrypto}),
+     * but if you use the rust crypto implementation ({@link MatrixClient#initRustCrypto}) and the device
+     * previously used legacy crypto (so must be migrated), then this must still be provided, so that the
+     * data can be migrated from the legacy store.
      */
     pickleKey?: string;
 
@@ -1480,13 +1480,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
 
         this.on(ClientEvent.Sync, this.startMatrixRTC);
 
-        // backwards compat for when 'opts' was 'historyLen'.
-        if (typeof opts === "number") {
-            opts = {
-                initialSyncLimit: opts,
-            };
-        }
-
         // Create our own user object artificially (instead of waiting for sync)
         // so it's always available, even if the user is not in any rooms etc.
         const userId = this.getUserId();
@@ -2229,17 +2222,24 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * An alternative to {@link initCrypto}.
      *
-     * *WARNING*: this API is very experimental, should not be used in production, and may change without notice!
-     *    Eventually it will be deprecated and `initCrypto` will do the same thing.
-     *
-     * @experimental
-     *
-     * @param useIndexedDB - True to use an indexeddb store, false to use an in-memory store. Defaults to 'true'.
+     * @param args.useIndexedDB - True to use an indexeddb store, false to use an in-memory store. Defaults to 'true'.
+     * @param args.storageKey - A key with which to encrypt the indexeddb store. If provided, it must be exactly
+     *    32 bytes of data, and must be the same each time the client is initialised for a given device.
+     *    If both this and `storagePassword` are unspecified, the store will be unencrypted.
+     * @param args.storagePassword - An alternative to `storageKey`. A password which will be used to derive a key to
+     *    encrypt the store with. Deriving a key from a password is (deliberately) a slow operation, so prefer
+     *    to pass a `storageKey` directly where possible.
      *
      * @returns a Promise which will resolve when the crypto layer has been
      *    successfully initialised.
      */
-    public async initRustCrypto({ useIndexedDB = true }: { useIndexedDB?: boolean } = {}): Promise<void> {
+    public async initRustCrypto(
+        args: {
+            useIndexedDB?: boolean;
+            storageKey?: Uint8Array;
+            storagePassword?: string;
+        } = {},
+    ): Promise<void> {
         if (this.cryptoBackend) {
             this.logger.warn("Attempt to re-initialise e2e encryption on MatrixClient");
             return;
@@ -2272,11 +2272,15 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             deviceId: deviceId,
             secretStorage: this.secretStorage,
             cryptoCallbacks: this.cryptoCallbacks,
-            storePrefix: useIndexedDB ? RUST_SDK_STORE_PREFIX : null,
-            storePassphrase: this.pickleKey,
+            storePrefix: args.useIndexedDB === false ? null : RUST_SDK_STORE_PREFIX,
+            storeKey: args.storageKey,
+
+            // temporary compatibility hack: if there is no storageKey nor storagePassword, fall back to the pickleKey
+            storePassphrase: args.storagePassword ?? this.pickleKey,
+
             legacyCryptoStore: this.cryptoStore,
             legacyPickleKey: this.pickleKey ?? "DEFAULT_KEY",
-            legacyMigrationProgressListener: (progress, total) => {
+            legacyMigrationProgressListener: (progress: number, total: number): void => {
                 this.emit(CryptoEvent.LegacyCryptoStoreMigrationProgress, progress, total);
             },
         });
@@ -2895,7 +2899,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param event - event to be checked
      * @returns The event information.
-     * @deprecated Prefer {@link CryptoApi.getEncryptionInfoForEvent | `CryptoApi.getEncryptionInfoForEvent`}.
+     * @deprecated Prefer {@link Crypto.CryptoApi.getEncryptionInfoForEvent | `CryptoApi.getEncryptionInfoForEvent`}.
      */
     public getEventEncryptionInfo(event: MatrixEvent): IEncryptedEventInfo {
         if (!this.cryptoBackend) {
@@ -3313,7 +3317,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *     trust information (as returned by isKeyBackupTrusted)
      *     in trustInfo.
      *
-     * @deprecated Prefer {@link CryptoApi.checkKeyBackupAndEnable}.
+     * @deprecated Prefer {@link Crypto.CryptoApi.checkKeyBackupAndEnable}.
      */
     public checkKeyBackup(): Promise<IKeyBackupCheck | null> {
         if (!this.crypto) {
@@ -3370,7 +3374,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *     the server, otherwise false. If we haven't completed a successful check
      *     of key backup status yet, returns null.
      *
-     * @deprecated Prefer direct access to {@link CryptoApi.getActiveSessionBackupVersion}:
+     * @deprecated Prefer direct access to {@link Crypto.CryptoApi.getActiveSessionBackupVersion}:
      *
      * ```javascript
      * let enabled = (await client.getCrypto().getActiveSessionBackupVersion()) !== null;
@@ -3390,7 +3394,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * @param info - Backup information object as returned by getKeyBackupVersion
      * @returns Promise which resolves when complete.
      *
-     * @deprecated Do not call this directly. Instead call {@link CryptoApi.checkKeyBackupAndEnable}.
+     * @deprecated Do not call this directly. Instead call {@link Crypto.CryptoApi.checkKeyBackupAndEnable}.
      */
     public enableKeyBackup(info: IKeyBackupInfo): Promise<void> {
         if (!this.crypto) {
@@ -3852,12 +3856,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         if (!backupInfo.version) {
             throw new Error("Backup version must be defined");
         }
+        const backupVersion = backupInfo.version!;
 
         let totalKeyCount = 0;
         let totalFailures = 0;
         let totalImported = 0;
 
-        const path = this.makeKeyBackupPath(targetRoomId, targetSessionId, backupInfo.version);
+        const path = this.makeKeyBackupPath(targetRoomId, targetSessionId, backupVersion);
 
         const backupDecryptor = await this.cryptoBackend.getBackupDecryptor(backupInfo, privKey);
 
@@ -3871,7 +3876,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             // Cache the key, if possible.
             // This is async.
             this.cryptoBackend
-                .storeSessionBackupPrivateKey(privKey, backupInfo.version)
+                .storeSessionBackupPrivateKey(privKey, backupVersion)
                 .catch((e) => {
                     this.logger.warn("Error caching session backup key:", e);
                 })
@@ -3911,7 +3916,8 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                     async (chunk) => {
                         // We have a chunk of decrypted keys: import them
                         try {
-                            await this.cryptoBackend!.importBackedUpRoomKeys(chunk, {
+                            const backupVersion = backupInfo.version!;
+                            await this.cryptoBackend!.importBackedUpRoomKeys(chunk, backupVersion, {
                                 untrusted,
                             });
                             totalImported += chunk.length;
@@ -3941,7 +3947,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                 for (const k of keys) {
                     k.room_id = targetRoomId!;
                 }
-                await this.cryptoBackend.importBackedUpRoomKeys(keys, {
+                await this.cryptoBackend.importBackedUpRoomKeys(keys, backupVersion, {
                     progressCallback,
                     untrusted,
                 });
@@ -3955,7 +3961,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
                     key.room_id = targetRoomId!;
                     key.session_id = targetSessionId!;
 
-                    await this.cryptoBackend.importBackedUpRoomKeys([key], {
+                    await this.cryptoBackend.importBackedUpRoomKeys([key], backupVersion, {
                         progressCallback,
                         untrusted,
                     });
@@ -7888,16 +7894,10 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         password: string,
         sessionId: string | null,
         auth: { session?: string; type: string },
-        bindThreepids?: boolean | null | { email?: boolean; msisdn?: boolean },
+        bindThreepids?: { email?: boolean; msisdn?: boolean },
         guestAccessToken?: string,
         inhibitLogin?: boolean,
     ): Promise<RegisterResponse> {
-        // backwards compat
-        if (bindThreepids === true) {
-            bindThreepids = { email: true };
-        } else if (bindThreepids === null || bindThreepids === undefined || bindThreepids === false) {
-            bindThreepids = {};
-        }
         if (sessionId) {
             auth.session = sessionId;
         }
@@ -7912,27 +7912,12 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         if (password !== undefined && password !== null) {
             params.password = password;
         }
-        if (bindThreepids.email) {
-            params.bind_email = true;
-        }
-        if (bindThreepids.msisdn) {
-            params.bind_msisdn = true;
-        }
         if (guestAccessToken !== undefined && guestAccessToken !== null) {
             params.guest_access_token = guestAccessToken;
         }
         if (inhibitLogin !== undefined && inhibitLogin !== null) {
             params.inhibit_login = inhibitLogin;
         }
-        // Temporary parameter added to make the register endpoint advertise
-        // msisdn flows. This exists because there are clients that break
-        // when given stages they don't recognise. This parameter will cease
-        // to be necessary once these old clients are gone.
-        // Only send it if we send any params at all (the password param is
-        // mandatory, so if we send any params, we'll send the password param)
-        if (password !== undefined && password !== null) {
-            params.x_show_msisdn = true;
-        }
 
         return this.registerRequest(params);
     }
diff --git a/src/common-crypto/CryptoBackend.ts b/src/common-crypto/CryptoBackend.ts
index 401e4a09119..7a36dc560e9 100644
--- a/src/common-crypto/CryptoBackend.ts
+++ b/src/common-crypto/CryptoBackend.ts
@@ -113,10 +113,11 @@ export interface CryptoBackend extends SyncCryptoCallbacks, CryptoApi {
      * Import a list of room keys restored from backup
      *
      * @param keys - a list of session export objects
+     * @param backupVersion - the version of the backup these keys came from.
      * @param opts - options object
      * @returns a promise which resolves once the keys have been imported
      */
-    importBackedUpRoomKeys(keys: IMegolmSessionData[], opts?: ImportRoomKeysOpts): Promise<void>;
+    importBackedUpRoomKeys(keys: IMegolmSessionData[], backupVersion: string, opts?: ImportRoomKeysOpts): Promise<void>;
 }
 
 /** The methods which crypto implementations should expose to the Sync api
diff --git a/src/crypto-api/keybackup.ts b/src/crypto-api/keybackup.ts
index edb4908ec3a..71c47d6834f 100644
--- a/src/crypto-api/keybackup.ts
+++ b/src/crypto-api/keybackup.ts
@@ -63,7 +63,7 @@ export interface BackupTrustInfo {
 }
 
 /**
- * The result of {@link CryptoApi.checkKeyBackupAndEnable}.
+ * The result of {@link Crypto.CryptoApi.checkKeyBackupAndEnable}.
  */
 export interface KeyBackupCheck {
     backupInfo: KeyBackupInfo;
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index ff62c429c9f..4379c2e1272 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -643,7 +643,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi#getVersion}.
+     * Implementation of {@link Crypto.CryptoApi#getVersion}.
      */
     public getVersion(): string {
         const olmVersionTuple = Crypto.getOlmVersion();
@@ -803,7 +803,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi#getCrossSigningStatus}
+     * Implementation of {@link Crypto.CryptoApi#getCrossSigningStatus}
      */
     public async getCrossSigningStatus(): Promise<CrossSigningStatus> {
         const publicKeysOnDevice = Boolean(this.crossSigningInfo.getId());
@@ -1167,7 +1167,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi#resetKeyBackup}.
+     * Implementation of {@link Crypto.CryptoApi#resetKeyBackup}.
      */
     public async resetKeyBackup(): Promise<void> {
         // Delete existing ones
@@ -1203,7 +1203,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi#deleteKeyBackupVersion}.
+     * Implementation of {@link Crypto.CryptoApi#deleteKeyBackupVersion}.
      */
     public async deleteKeyBackupVersion(version: string): Promise<void> {
         await this.backupManager.deleteKeyBackupVersion(version);
@@ -1350,7 +1350,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Get the current status of key backup.
      *
-     * Implementation of {@link CryptoApi.getActiveSessionBackupVersion}.
+     * Implementation of {@link Crypto.CryptoApi.getActiveSessionBackupVersion}.
      */
     public async getActiveSessionBackupVersion(): Promise<string | null> {
         if (this.backupManager.getKeyBackupEnabled()) {
@@ -1372,7 +1372,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Force a re-check of the key backup and enable/disable it as appropriate.
      *
-     * Implementation of {@link CryptoApi.checkKeyBackupAndEnable}.
+     * Implementation of {@link Crypto.CryptoApi.checkKeyBackupAndEnable}.
      */
     public async checkKeyBackupAndEnable(): Promise<KeyBackupCheck | null> {
         const checkResult = await this.backupManager.checkKeyBackup();
@@ -1589,7 +1589,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi.getUserVerificationStatus}.
+     * Implementation of {@link Crypto.CryptoApi.getUserVerificationStatus}.
      */
     public async getUserVerificationStatus(userId: string): Promise<UserTrustLevel> {
         return this.checkUserTrust(userId);
@@ -1888,7 +1888,11 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Implementation of {@link CryptoBackend#importBackedUpRoomKeys}.
      */
-    public importBackedUpRoomKeys(keys: IMegolmSessionData[], opts: ImportRoomKeysOpts = {}): Promise<void> {
+    public importBackedUpRoomKeys(
+        keys: IMegolmSessionData[],
+        backupVersion: string,
+        opts: ImportRoomKeysOpts = {},
+    ): Promise<void> {
         opts.source = "backup";
         return this.importRoomKeys(keys, opts);
     }
@@ -1986,7 +1990,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      *
      * @returns base64-encoded ed25519 key.
      *
-     * @deprecated Use {@link CryptoApi#getOwnDeviceKeys}.
+     * @deprecated Use {@link Crypto.CryptoApi#getOwnDeviceKeys}.
      */
     public getDeviceEd25519Key(): string | null {
         return this.olmDevice.deviceEd25519Key;
@@ -1997,14 +2001,14 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      *
      * @returns base64-encoded curve25519 key.
      *
-     * @deprecated Use {@link CryptoApi#getOwnDeviceKeys}
+     * @deprecated Use {@link Crypto.CryptoApi#getOwnDeviceKeys}
      */
     public getDeviceCurve25519Key(): string | null {
         return this.olmDevice.deviceCurve25519Key;
     }
 
     /**
-     * Implementation of {@link CryptoApi#getOwnDeviceKeys}.
+     * Implementation of {@link Crypto.CryptoApi#getOwnDeviceKeys}.
      */
     public async getOwnDeviceKeys(): Promise<OwnDeviceKeys> {
         if (!this.olmDevice.deviceCurve25519Key) {
@@ -2340,7 +2344,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Mark the given device as locally verified.
      *
-     * Implementation of {@link CryptoApi#setDeviceVerified}.
+     * Implementation of {@link Crypto.CryptoApi#setDeviceVerified}.
      */
     public async setDeviceVerified(userId: string, deviceId: string, verified = true): Promise<void> {
         await this.setDeviceVerification(userId, deviceId, verified);
@@ -2349,7 +2353,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     /**
      * Blindly cross-sign one of our other devices.
      *
-     * Implementation of {@link CryptoApi#crossSignDevice}.
+     * Implementation of {@link Crypto.CryptoApi#crossSignDevice}.
      */
     public async crossSignDevice(deviceId: string): Promise<void> {
         await this.setDeviceVerified(this.userId, deviceId, true);
@@ -2785,7 +2789,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi.getEncryptionInfoForEvent}.
+     * Implementation of {@link Crypto.CryptoApi.getEncryptionInfoForEvent}.
      */
     public async getEncryptionInfoForEvent(event: MatrixEvent): Promise<EventEncryptionInfo | null> {
         const encryptionInfo = this.getEventEncryptionInfo(event);
@@ -4268,7 +4272,7 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
     }
 
     /**
-     * Implementation of {@link CryptoApi#isEncryptionEnabledInRoom}.
+     * Implementation of {@link Crypto.CryptoApi#isEncryptionEnabledInRoom}.
      */
     public async isEncryptionEnabledInRoom(roomId: string): Promise<boolean> {
         return this.isRoomEncrypted(roomId);
diff --git a/src/matrix.ts b/src/matrix.ts
index ed71f7dfcac..793a894e0d0 100644
--- a/src/matrix.ts
+++ b/src/matrix.ts
@@ -114,20 +114,6 @@ export { LocationAssetType } from "./@types/location";
  */
 export * as Crypto from "./crypto-api";
 
-/**
- * Backwards compatibility re-export
- * @internal
- * @deprecated use {@link Crypto.CryptoApi}
- */
-export type { CryptoApi } from "./crypto-api";
-
-/**
- * Backwards compatibility re-export
- * @internal
- * @deprecated use {@link Crypto.DeviceVerificationStatus}
- */
-export { DeviceVerificationStatus } from "./crypto-api";
-
 let cryptoStoreFactory = (): CryptoStore => new MemoryCryptoStore();
 
 /**
diff --git a/src/models/MSC3089TreeSpace.ts b/src/models/MSC3089TreeSpace.ts
index 76aae65588c..6dc1b6fbb63 100644
--- a/src/models/MSC3089TreeSpace.ts
+++ b/src/models/MSC3089TreeSpace.ts
@@ -35,7 +35,7 @@ import { ISendEventResponse } from "../@types/requests";
 import { FileType } from "../http-api";
 import { KnownMembership } from "../@types/membership";
 import { RoomPowerLevelsEventContent, SpaceChildEventContent } from "../@types/state_events";
-import { EncryptedFile, FileContent } from "../@types/media";
+import type { EncryptedFile, FileContent } from "../@types/media";
 
 /**
  * The recommended defaults for a tree space's power levels. Note that this
diff --git a/src/models/event-timeline-set.ts b/src/models/event-timeline-set.ts
index 38d47cd2147..e64d118fdd5 100644
--- a/src/models/event-timeline-set.ts
+++ b/src/models/event-timeline-set.ts
@@ -592,43 +592,8 @@ export class EventTimelineSet extends TypedEventEmitter<EmittedEvents, EventTime
      */
     public addLiveEvent(
         event: MatrixEvent,
-        { duplicateStrategy, fromCache, roomState, timelineWasEmpty }: IAddLiveEventOptions,
-    ): void;
-    /**
-     * @deprecated In favor of the overload with `IAddLiveEventOptions`
-     */
-    public addLiveEvent(
-        event: MatrixEvent,
-        duplicateStrategy?: DuplicateStrategy,
-        fromCache?: boolean,
-        roomState?: RoomState,
-    ): void;
-    public addLiveEvent(
-        event: MatrixEvent,
-        duplicateStrategyOrOpts?: DuplicateStrategy | IAddLiveEventOptions,
-        fromCache = false,
-        roomState?: RoomState,
+        { duplicateStrategy, fromCache, roomState, timelineWasEmpty }: IAddLiveEventOptions = {},
     ): void {
-        let duplicateStrategy = (duplicateStrategyOrOpts as DuplicateStrategy) || DuplicateStrategy.Ignore;
-        let timelineWasEmpty: boolean | undefined;
-        if (typeof duplicateStrategyOrOpts === "object") {
-            ({
-                duplicateStrategy = DuplicateStrategy.Ignore,
-                fromCache = false,
-                roomState,
-                timelineWasEmpty,
-            } = duplicateStrategyOrOpts);
-        } else if (duplicateStrategyOrOpts !== undefined) {
-            // Deprecation warning
-            // FIXME: Remove after 2023-06-01 (technical debt)
-            logger.warn(
-                "Overload deprecated: " +
-                    "`EventTimelineSet.addLiveEvent(event, duplicateStrategy?, fromCache?, roomState?)` " +
-                    "is deprecated in favor of the overload with " +
-                    "`EventTimelineSet.addLiveEvent(event, IAddLiveEventOptions)`",
-            );
-        }
-
         if (this.filter) {
             const events = this.filter.filterRoomTimeline([event]);
             if (!events.length) {
diff --git a/src/models/event-timeline.ts b/src/models/event-timeline.ts
index a20dac880e4..912dcaf2130 100644
--- a/src/models/event-timeline.ts
+++ b/src/models/event-timeline.ts
@@ -14,7 +14,6 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { logger } from "../logger";
 import { IMarkerFoundOptions, RoomState } from "./room-state";
 import { EventTimelineSet } from "./event-timeline-set";
 import { MatrixEvent } from "./event";
@@ -361,30 +360,10 @@ export class EventTimeline {
      * @param event - new event
      * @param options - addEvent options
      */
-    public addEvent(event: MatrixEvent, { toStartOfTimeline, roomState, timelineWasEmpty }: IAddEventOptions): void;
-    /**
-     * @deprecated In favor of the overload with `IAddEventOptions`
-     */
-    public addEvent(event: MatrixEvent, toStartOfTimeline: boolean, roomState?: RoomState): void;
     public addEvent(
         event: MatrixEvent,
-        toStartOfTimelineOrOpts: boolean | IAddEventOptions,
-        roomState?: RoomState,
+        { toStartOfTimeline, roomState, timelineWasEmpty }: IAddEventOptions = { toStartOfTimeline: false },
     ): void {
-        let toStartOfTimeline = !!toStartOfTimelineOrOpts;
-        let timelineWasEmpty: boolean | undefined;
-        if (typeof toStartOfTimelineOrOpts === "object") {
-            ({ toStartOfTimeline, roomState, timelineWasEmpty } = toStartOfTimelineOrOpts);
-        } else if (toStartOfTimelineOrOpts !== undefined) {
-            // Deprecation warning
-            // FIXME: Remove after 2023-06-01 (technical debt)
-            logger.warn(
-                "Overload deprecated: " +
-                    "`EventTimeline.addEvent(event, toStartOfTimeline, roomState?)` " +
-                    "is deprecated in favor of the overload with `EventTimeline.addEvent(event, IAddEventOptions)`",
-            );
-        }
-
         if (!roomState) {
             roomState = toStartOfTimeline ? this.startState : this.endState;
         }
diff --git a/src/models/event.ts b/src/models/event.ts
index 3e5df8fbf7c..7b9365aad50 100644
--- a/src/models/event.ts
+++ b/src/models/event.ts
@@ -98,19 +98,6 @@ export interface IEvent {
     membership?: Membership;
     unsigned: IUnsigned;
     redacts?: string;
-
-    /**
-     * @deprecated in favour of `sender`
-     */
-    user_id?: string;
-    /**
-     * @deprecated in favour of `unsigned.prev_content`
-     */
-    prev_content?: IContent;
-    /**
-     * @deprecated in favour of `origin_server_ts`
-     */
-    age?: number;
 }
 
 export interface IAggregatedRelation {
@@ -495,7 +482,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * @returns The user ID, e.g. `@alice:matrix.org`
      */
     public getSender(): string | undefined {
-        return this.event.sender || this.event.user_id; // v2 / v1
+        return this.event.sender; // v2 / v1
     }
 
     /**
@@ -669,7 +656,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      */
     public getPrevContent(): IContent {
         // v2 then v1 then default
-        return this.getUnsigned().prev_content || this.event.prev_content || {};
+        return this.getUnsigned().prev_content || {};
     }
 
     /**
@@ -693,7 +680,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * @returns The age of this event in milliseconds.
      */
     public getAge(): number | undefined {
-        return this.getUnsigned().age || this.event.age; // v2 / v1
+        return this.getUnsigned().age;
     }
 
     /**
@@ -1084,7 +1071,7 @@ export class MatrixEvent extends TypedEventEmitter<MatrixEventEmittedEvents, Mat
      * signing the public curve25519 key with the ed25519 key.
      *
      * In general, applications should not use this method directly, but should
-     * instead use {@link CryptoApi#getEncryptionInfoForEvent}.
+     * instead use {@link Crypto.CryptoApi#getEncryptionInfoForEvent}.
      */
     public getClaimedEd25519Key(): string | null {
         return this.claimedEd25519Key;
diff --git a/src/models/room.ts b/src/models/room.ts
index 974d0ab9fe7..d8b90a60856 100644
--- a/src/models/room.ts
+++ b/src/models/room.ts
@@ -405,12 +405,6 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
      */
     private threads = new Map<string, Thread>();
 
-    /**
-     * @deprecated This value is unreliable. It may not contain the last thread.
-     *             Use {@link Room.getLastThread} instead.
-     */
-    public lastThread?: Thread;
-
     /**
      * A mapping of eventId to all visibility changes to apply
      * to the event, by chronological order, as per
@@ -1382,32 +1376,6 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         }
     }
 
-    /**
-     * Returns whether there are any devices in the room that are unverified
-     *
-     * Note: Callers should first check if crypto is enabled on this device. If it is
-     * disabled, then we aren't tracking room devices at all, so we can't answer this, and an
-     * error will be thrown.
-     *
-     * @returns the result
-     *
-     * @deprecated Not supported under rust crypto. Instead, call {@link Room.getEncryptionTargetMembers},
-     * {@link CryptoApi.getUserDeviceInfo}, and {@link CryptoApi.getDeviceVerificationStatus}.
-     */
-    public async hasUnverifiedDevices(): Promise<boolean> {
-        if (!this.hasEncryptionStateEvent()) {
-            return false;
-        }
-        const e2eMembers = await this.getEncryptionTargetMembers();
-        for (const member of e2eMembers) {
-            const devices = this.client.getStoredDevicesForUser(member.userId);
-            if (devices.some((device) => device.isUnverified())) {
-                return true;
-            }
-        }
-        return false;
-    }
-
     /**
      * Return the timeline sets for this room.
      * @returns array of timeline sets for this room
@@ -2458,15 +2426,6 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
         // and pass the event through this.
         thread.addEvents(events, false);
 
-        const isNewer =
-            this.lastThread?.rootEvent &&
-            rootEvent?.localTimestamp &&
-            this.lastThread.rootEvent?.localTimestamp < rootEvent?.localTimestamp;
-
-        if (!this.lastThread || isNewer) {
-            this.lastThread = thread;
-        }
-
         // We need to update the thread root events, but the thread may not be ready yet.
         // If it isn't, it will fire ThreadEvent.Update when it is and we'll call updateThreadRootEvents then.
         if (this.threadsReady && thread.initialEventsFetched) {
@@ -2896,39 +2855,8 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
      * @param addLiveEventOptions - addLiveEvent options
      * @throws If `duplicateStrategy` is not falsey, 'replace' or 'ignore'.
      */
-    public async addLiveEvents(events: MatrixEvent[], addLiveEventOptions?: IAddLiveEventOptions): Promise<void>;
-    /**
-     * @deprecated In favor of the overload with `IAddLiveEventOptions`
-     */
-    public async addLiveEvents(
-        events: MatrixEvent[],
-        duplicateStrategy?: DuplicateStrategy,
-        fromCache?: boolean,
-    ): Promise<void>;
-    public async addLiveEvents(
-        events: MatrixEvent[],
-        duplicateStrategyOrOpts?: DuplicateStrategy | IAddLiveEventOptions,
-        fromCache = false,
-    ): Promise<void> {
-        let duplicateStrategy: DuplicateStrategy | undefined = duplicateStrategyOrOpts as DuplicateStrategy;
-        let timelineWasEmpty: boolean | undefined = false;
-        if (typeof duplicateStrategyOrOpts === "object") {
-            ({
-                duplicateStrategy,
-                fromCache = false,
-                /* roomState, (not used here) */
-                timelineWasEmpty,
-            } = duplicateStrategyOrOpts);
-        } else if (duplicateStrategyOrOpts !== undefined) {
-            // Deprecation warning
-            // FIXME: Remove after 2023-06-01 (technical debt)
-            logger.warn(
-                "Overload deprecated: " +
-                    "`Room.addLiveEvents(events, duplicateStrategy?, fromCache?)` " +
-                    "is deprecated in favor of the overload with `Room.addLiveEvents(events, IAddLiveEventOptions)`",
-            );
-        }
-
+    public async addLiveEvents(events: MatrixEvent[], addLiveEventOptions?: IAddLiveEventOptions): Promise<void> {
+        const { duplicateStrategy, fromCache, timelineWasEmpty = false } = addLiveEventOptions ?? {};
         if (duplicateStrategy && ["replace", "ignore"].indexOf(duplicateStrategy) === -1) {
             throw new Error("duplicateStrategy MUST be either 'replace' or 'ignore'");
         }
@@ -3229,7 +3157,7 @@ export class Room extends ReadReceipt<RoomEmittedEvents, RoomEventHandlerMap> {
                                 content: strippedEvent.content,
                                 event_id: "$fake" + Date.now(),
                                 room_id: this.roomId,
-                                user_id: this.myUserId, // technically a lie
+                                sender: this.myUserId, // technically a lie
                             }),
                         ]);
                     }
diff --git a/src/rust-crypto/PerSessionKeyBackupDownloader.ts b/src/rust-crypto/PerSessionKeyBackupDownloader.ts
index 7642d52f9d9..ad5a649c51f 100644
--- a/src/rust-crypto/PerSessionKeyBackupDownloader.ts
+++ b/src/rust-crypto/PerSessionKeyBackupDownloader.ts
@@ -57,10 +57,14 @@ class KeyDownloadRateLimitError extends Error {
 /** Details of a megolm session whose key we are trying to fetch. */
 type SessionInfo = { roomId: string; megolmSessionId: string };
 
-/** Holds the current backup decryptor and version that should be used. */
+/** Holds the current backup decryptor and version that should be used.
+ *
+ * This is intended to be used as an immutable object (a new instance should be created if the configuration changes),
+ * and some of the logic relies on that, so the properties are marked as `readonly`.
+ */
 type Configuration = {
-    backupVersion: string;
-    decryptor: BackupDecryptor;
+    readonly backupVersion: string;
+    readonly decryptor: BackupDecryptor;
 };
 
 /**
@@ -392,7 +396,7 @@ export class PerSessionKeyBackupDownloader {
         for (const k of keys) {
             k.room_id = sessionInfo.roomId;
         }
-        await this.backupManager.importBackedUpRoomKeys(keys);
+        await this.backupManager.importBackedUpRoomKeys(keys, configuration.backupVersion);
     }
 
     /**
diff --git a/src/rust-crypto/backup.ts b/src/rust-crypto/backup.ts
index 5c9c5772e2b..8eb84887448 100644
--- a/src/rust-crypto/backup.ts
+++ b/src/rust-crypto/backup.ts
@@ -239,7 +239,11 @@ export class RustBackupManager extends TypedEventEmitter<RustBackupCryptoEvents,
     /**
      * Implementation of {@link CryptoBackend#importBackedUpRoomKeys}.
      */
-    public async importBackedUpRoomKeys(keys: IMegolmSessionData[], opts?: ImportRoomKeysOpts): Promise<void> {
+    public async importBackedUpRoomKeys(
+        keys: IMegolmSessionData[],
+        backupVersion: string,
+        opts?: ImportRoomKeysOpts,
+    ): Promise<void> {
         const keysByRoom: Map<RustSdkCryptoJs.RoomId, Map<string, IMegolmSessionData>> = new Map();
         for (const key of keys) {
             const roomId = new RustSdkCryptoJs.RoomId(key.room_id);
@@ -259,6 +263,7 @@ export class RustBackupManager extends TypedEventEmitter<RustBackupCryptoEvents,
                 };
                 opts?.progressCallback?.(importOpt);
             },
+            backupVersion,
         );
     }
 
diff --git a/src/rust-crypto/index.ts b/src/rust-crypto/index.ts
index 6defede1e95..dc9a42af743 100644
--- a/src/rust-crypto/index.ts
+++ b/src/rust-crypto/index.ts
@@ -64,13 +64,21 @@ export async function initRustCrypto(args: {
     storePrefix: string | null;
 
     /**
-     * A passphrase to use to encrypt the indexeddbs created by rust-crypto.
+     * A passphrase to use to encrypt the indexeddb created by rust-crypto.
      *
-     * Ignored if `storePrefix` is null. If this is `undefined` (and `storePrefix` is not null), the indexeddbs
-     * will be unencrypted.
+     * Ignored if `storePrefix` is null, or `storeKey` is set.  If neither this nor `storeKey` is set
+     * (and `storePrefix` is not null), the indexeddb will be unencrypted.
      */
     storePassphrase?: string;
 
+    /**
+     * A key to use to encrypt the indexeddb created by rust-crypto.
+     *
+     * Ignored if `storePrefix` is null. Otherwise, if it is set, it must be a 32-byte cryptographic key, which
+     * will be used to encrypt the indexeddb. See also `storePassphrase`.
+     */
+    storeKey?: Uint8Array;
+
     /** If defined, we will check if any data needs migrating from this store to the rust store. */
     legacyCryptoStore?: CryptoStore;
 
@@ -94,10 +102,16 @@ export async function initRustCrypto(args: {
     new RustSdkCryptoJs.Tracing(RustSdkCryptoJs.LoggerLevel.Debug).turnOn();
 
     logger.debug("Opening Rust CryptoStore");
-    const storeHandle: StoreHandle = await StoreHandle.open(
-        args.storePrefix ?? undefined,
-        (args.storePrefix && args.storePassphrase) ?? undefined,
-    );
+    let storeHandle;
+    if (args.storePrefix) {
+        if (args.storeKey) {
+            storeHandle = await StoreHandle.openWithKey(args.storePrefix, args.storeKey);
+        } else {
+            storeHandle = await StoreHandle.open(args.storePrefix, args.storePassphrase);
+        }
+    } else {
+        storeHandle = await StoreHandle.open();
+    }
 
     if (args.legacyCryptoStore) {
         // We have a legacy crypto store, which we may need to migrate from.
diff --git a/src/rust-crypto/libolm_migration.ts b/src/rust-crypto/libolm_migration.ts
index 2738f88f6c8..ec01847262c 100644
--- a/src/rust-crypto/libolm_migration.ts
+++ b/src/rust-crypto/libolm_migration.ts
@@ -83,6 +83,19 @@ export async function migrateFromLegacyCrypto(args: {
     }
 
     await legacyStore.startup();
+
+    let accountPickle: string | null = null;
+    await legacyStore.doTxn("readonly", [IndexedDBCryptoStore.STORE_ACCOUNT], (txn) => {
+        legacyStore.getAccount(txn, (acctPickle) => {
+            accountPickle = acctPickle;
+        });
+    });
+    if (!accountPickle) {
+        // This store is not properly set up. Nothing to migrate.
+        logger.debug("Legacy crypto store is not set up (no account found). Not migrating.");
+        return;
+    }
+
     let migrationState = await legacyStore.getMigrationState();
 
     if (migrationState >= MigrationState.MEGOLM_SESSIONS_MIGRATED) {
diff --git a/src/rust-crypto/rust-crypto.ts b/src/rust-crypto/rust-crypto.ts
index 29373fe3b48..8cbfba4b0c5 100644
--- a/src/rust-crypto/rust-crypto.ts
+++ b/src/rust-crypto/rust-crypto.ts
@@ -865,7 +865,7 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
     }
 
     /**
-     * Implementation of {@link CryptoApi.getEncryptionInfoForEvent}.
+     * Implementation of {@link Crypto.CryptoApi.getEncryptionInfoForEvent}.
      */
     public async getEncryptionInfoForEvent(event: MatrixEvent): Promise<EventEncryptionInfo | null> {
         return this.eventDecryptor.getEncryptionInfoForEvent(event);
@@ -1217,8 +1217,12 @@ export class RustCrypto extends TypedEventEmitter<RustCryptoEvents, RustCryptoEv
     /**
      * Implementation of {@link CryptoBackend#importBackedUpRoomKeys}.
      */
-    public async importBackedUpRoomKeys(keys: IMegolmSessionData[], opts?: ImportRoomKeysOpts): Promise<void> {
-        return await this.backupManager.importBackedUpRoomKeys(keys, opts);
+    public async importBackedUpRoomKeys(
+        keys: IMegolmSessionData[],
+        backupVersion: string,
+        opts?: ImportRoomKeysOpts,
+    ): Promise<void> {
+        return await this.backupManager.importBackedUpRoomKeys(keys, backupVersion, opts);
     }
 
     /**
diff --git a/src/sync-accumulator.ts b/src/sync-accumulator.ts
index 67d5e1d6802..eec811577b8 100644
--- a/src/sync-accumulator.ts
+++ b/src/sync-accumulator.ts
@@ -58,8 +58,6 @@ export interface IRoomEvent extends IMinimalEvent {
     event_id: string;
     sender: string;
     origin_server_ts: number;
-    /** @deprecated - legacy field */
-    age?: number;
 }
 
 export interface IStateEvent extends IRoomEvent {
@@ -498,7 +496,7 @@ export class SyncAccumulator {
                 if (transformedEvent.unsigned !== undefined) {
                     transformedEvent.unsigned = Object.assign({}, transformedEvent.unsigned);
                 }
-                const age = e.unsigned ? e.unsigned.age : e.age;
+                const age = e.unsigned?.age;
                 if (age !== undefined) transformedEvent._localTs = Date.now() - age;
             } else {
                 transformedEvent = e;
diff --git a/src/utils.ts b/src/utils.ts
index 28e867eeda0..f3ad18d5735 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -748,12 +748,7 @@ export function safeSet<O extends Record<any, any>, K extends keyof O>(obj: O, p
 }
 
 export function noUnsafeEventProps(event: Partial<IEvent>): boolean {
-    return !(
-        unsafeProp(event.room_id) ||
-        unsafeProp(event.sender) ||
-        unsafeProp(event.user_id) ||
-        unsafeProp(event.event_id)
-    );
+    return !(unsafeProp(event.room_id) || unsafeProp(event.sender) || unsafeProp(event.event_id));
 }
 
 export class MapWithDefault<K, V> extends Map<K, V> {
diff --git a/yarn.lock b/yarn.lock
index 51c6c910d10..cf6d64c5b80 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1772,10 +1772,10 @@
     "@jridgewell/resolve-uri" "^3.1.0"
     "@jridgewell/sourcemap-codec" "^1.4.14"
 
-"@matrix-org/matrix-sdk-crypto-wasm@^4.9.0":
-  version "4.9.0"
-  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-wasm/-/matrix-sdk-crypto-wasm-4.9.0.tgz#9dfed83e33f760650596c4e5c520e5e4c53355d2"
-  integrity sha512-/bgA4QfE7qkK6GFr9hnhjAvRSebGrmEJxukU0ukbudZcYvbzymoBBM8j3HeULXZT8kbw8WH6z63txYTMCBSDOA==
+"@matrix-org/matrix-sdk-crypto-wasm@^5.0.0":
+  version "5.0.0"
+  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-wasm/-/matrix-sdk-crypto-wasm-5.0.0.tgz#f45a7bccaad218c05bcf9e7c8ca783c9d9a07af4"
+  integrity sha512-37ASjCKSTU5ycGfkP+LUXG4Ok6OAf6vE+1qU6uwWhe6FwadCS3vVWzJYd/3d9BQFwsx4GhFTIAXrW4iLG85rmQ==
 
 "@matrix-org/olm@3.2.15":
   version "3.2.15"