diff --git a/spec/unit/rust-crypto/rust-crypto.spec.ts b/spec/unit/rust-crypto/rust-crypto.spec.ts
index 1297003b74f..a0c9a47763f 100644
--- a/spec/unit/rust-crypto/rust-crypto.spec.ts
+++ b/spec/unit/rust-crypto/rust-crypto.spec.ts
@@ -98,6 +98,11 @@ describe("RustCrypto", () => {
         await expect(rustCrypto.isCrossSigningReady()).resolves.toBe(false);
     });
 
+    it("getCrossSigningKeyId", async () => {
+        const rustCrypto = await makeTestRustCrypto();
+        await expect(rustCrypto.getCrossSigningKeyId()).resolves.toBe(null);
+    });
+
     it("bootstrapCrossSigning", async () => {
         const rustCrypto = await makeTestRustCrypto();
         await rustCrypto.bootstrapCrossSigning({});
diff --git a/src/client.ts b/src/client.ts
index a037a5e4f55..defd1aa9f9e 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -2567,14 +2567,13 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     }
 
     /**
-     * Get the user's cross-signing key ID.
-     *
-     * The cross-signing API is currently UNSTABLE and may change without notice.
+     * Get the ID of one of the user's cross-signing keys
      *
      * @param type - The type of key to get the ID of.  One of
      *     "master", "self_signing", or "user_signing".  Defaults to "master".
      *
      * @returns the key ID
+     * @deprecated prefer {@link CryptoApi#getCrossSigningKeyId}
      */
     public getCrossSigningId(type: CrossSigningKey | string = CrossSigningKey.Master): string | null {
         if (!this.crypto) {
diff --git a/src/crypto-api.ts b/src/crypto-api.ts
index 338bfee4637..6467ba1835f 100644
--- a/src/crypto-api.ts
+++ b/src/crypto-api.ts
@@ -19,6 +19,13 @@ import { Room } from "./models/room";
 import { DeviceMap } from "./models/device";
 import { UIAuthCallback } from "./interactive-auth";
 
+/** Types of cross-signing key */
+export enum CrossSigningKey {
+    Master = "master",
+    SelfSigning = "self_signing",
+    UserSigning = "user_signing",
+}
+
 /**
  * Public interface to the cryptography parts of the js-sdk
  *
@@ -137,6 +144,16 @@ export interface CryptoApi {
      */
     isCrossSigningReady(): Promise<boolean>;
 
+    /**
+     * Get the ID of one of the user's cross-signing keys.
+     *
+     * @param type - The type of key to get the ID of.  One of `CrossSigningKey.Master`, `CrossSigngingKey.SelfSigning`,
+     *     or `CrossSigningKey.UserSigning`.  Defaults to `CrossSigningKey.Master`.
+     *
+     * @returns If cross-signing has been initialised on this device, the ID of the given key. Otherwise, null
+     */
+    getCrossSigningKeyId(type?: CrossSigningKey): Promise<string | null>;
+
     /**
      * Bootstrap cross-signing by creating keys if needed.
      *
diff --git a/src/crypto/api.ts b/src/crypto/api.ts
index 571c3df78d3..97ead425dab 100644
--- a/src/crypto/api.ts
+++ b/src/crypto/api.ts
@@ -19,6 +19,7 @@ import { IKeyBackupInfo } from "./keybackup";
 import type { AddSecretStorageKeyOpts } from "../secret-storage";
 
 /* re-exports for backwards compatibility. */
+export { CrossSigningKey } from "../crypto-api";
 export type {
     AddSecretStorageKeyOpts as IAddSecretStorageKeyOpts,
     PassphraseInfo as IPassphraseInfo,
@@ -27,12 +28,6 @@ export type {
 
 // TODO: Merge this with crypto.js once converted
 
-export enum CrossSigningKey {
-    Master = "master",
-    SelfSigning = "self_signing",
-    UserSigning = "user_signing",
-}
-
 export interface IEncryptedEventInfo {
     /**
      * whether the event is encrypted (if not encrypted, some of the other properties may not be set)
diff --git a/src/crypto/index.ts b/src/crypto/index.ts
index 234bb2737ab..1e847152b14 100644
--- a/src/crypto/index.ts
+++ b/src/crypto/index.ts
@@ -35,7 +35,13 @@ import * as algorithms from "./algorithms";
 import { createCryptoStoreCacheCallbacks, CrossSigningInfo, DeviceTrustLevel, UserTrustLevel } from "./CrossSigning";
 import { EncryptionSetupBuilder } from "./EncryptionSetup";
 import { SecretStorage as LegacySecretStorage } from "./SecretStorage";
-import { ICreateSecretStorageOpts, IEncryptedEventInfo, IImportRoomKeysOpts, IRecoveryKey } from "./api";
+import {
+    CrossSigningKey,
+    ICreateSecretStorageOpts,
+    IEncryptedEventInfo,
+    IImportRoomKeysOpts,
+    IRecoveryKey,
+} from "./api";
 import { OutgoingRoomKeyRequestManager } from "./OutgoingRoomKeyRequestManager";
 import { IndexedDBCryptoStore } from "./store/indexeddb-crypto-store";
 import { VerificationBase } from "./verification/Base";
@@ -45,7 +51,7 @@ import { keyFromPassphrase } from "./key_passphrase";
 import { decodeRecoveryKey, encodeRecoveryKey } from "./recoverykey";
 import { VerificationRequest } from "./verification/request/VerificationRequest";
 import { InRoomChannel, InRoomRequests } from "./verification/request/InRoomChannel";
-import { ToDeviceChannel, ToDeviceRequests, Request } from "./verification/request/ToDeviceChannel";
+import { Request, ToDeviceChannel, ToDeviceRequests } from "./verification/request/ToDeviceChannel";
 import { IllegalMethod } from "./verification/IllegalMethod";
 import { KeySignatureUploadError } from "../errors";
 import { calculateKeyCheck, decryptAES, encryptAES } from "./aes";
@@ -54,7 +60,7 @@ import { BackupManager } from "./backup";
 import { IStore } from "../store";
 import { Room, RoomEvent } from "../models/room";
 import { RoomMember, RoomMemberEvent } from "../models/room-member";
-import { EventStatus, IEvent, MatrixEvent, MatrixEventEvent } from "../models/event";
+import { EventStatus, IContent, IEvent, MatrixEvent, MatrixEventEvent } from "../models/event";
 import { ToDeviceBatch } from "../models/ToDeviceMessage";
 import {
     ClientEvent,
@@ -70,7 +76,6 @@ import { ISyncStateData } from "../sync";
 import { CryptoStore } from "./store/base";
 import { IVerificationChannel } from "./verification/request/Channel";
 import { TypedEventEmitter } from "../models/typed-event-emitter";
-import { IContent } from "../models/event";
 import { IDeviceLists, ISyncResponse, IToDeviceEvent } from "../sync-accumulator";
 import { ISignatures } from "../@types/signed";
 import { IMessage } from "./algorithms/olm";
@@ -80,11 +85,11 @@ import { MapWithDefault, recursiveMapToObject } from "../utils";
 import {
     AccountDataClient,
     AddSecretStorageKeyOpts,
+    SECRET_STORAGE_ALGORITHM_V1_AES,
+    SecretStorageCallbacks,
     SecretStorageKeyDescription,
     SecretStorageKeyObject,
     SecretStorageKeyTuple,
-    SECRET_STORAGE_ALGORITHM_V1_AES,
-    SecretStorageCallbacks,
     ServerSideSecretStorageImpl,
 } from "../secret-storage";
 import { ISecretRequest } from "./SecretSharing";
@@ -1415,6 +1420,11 @@ export class Crypto extends TypedEventEmitter<CryptoEvent, CryptoEventHandlerMap
      *
      * @returns the key ID
      */
+    public getCrossSigningKeyId(type: CrossSigningKey = CrossSigningKey.Master): Promise<string | null> {
+        return Promise.resolve(this.getCrossSigningId(type));
+    }
+
+    // old name, for backwards compatibility
     public getCrossSigningId(type: string): string | null {
         return this.crossSigningInfo.getId(type);
     }
diff --git a/src/rust-crypto/rust-crypto.ts b/src/rust-crypto/rust-crypto.ts
index d92b7a9ca74..d96c916e477 100644
--- a/src/rust-crypto/rust-crypto.ts
+++ b/src/rust-crypto/rust-crypto.ts
@@ -35,6 +35,7 @@ import { deviceKeysToDeviceMap, rustDeviceToJsDevice } from "./device-converter"
 import { IDownloadKeyResult, IQueryKeysRequest } from "../client";
 import { Device, DeviceMap } from "../models/device";
 import { ServerSideSecretStorage } from "../secret-storage";
+import { CrossSigningKey } from "../crypto/api";
 
 /**
  * An implementation of {@link CryptoBackend} using the Rust matrix-sdk-crypto.
@@ -324,6 +325,14 @@ export class RustCrypto implements CryptoBackend {
         return false;
     }
 
+    /**
+     * Implementation of {@link CryptoApi#getCrossSigningKeyId}
+     */
+    public async getCrossSigningKeyId(type: CrossSigningKey = CrossSigningKey.Master): Promise<string | null> {
+        // TODO
+        return null;
+    }
+
     /**
      * Implementation of {@link CryptoApi#boostrapCrossSigning}
      */