diff --git a/README.md b/README.md
index ee41f49b0e2..add491156dd 100644
--- a/README.md
+++ b/README.md
@@ -11,6 +11,8 @@
 This is the [Matrix](https://matrix.org) Client-Server SDK for JavaScript and TypeScript. This SDK can be run in a
 browser or in Node.js.
 
+#### Minimum Matrix server version: v1.1
+
 The Matrix specification is constantly evolving - while this SDK aims for maximum backwards compatibility, it only
 guarantees that a feature will be supported for at least 4 spec releases. For example, if a feature the js-sdk supports
 is removed in v1.4 then the feature is _eligible_ for removal from the SDK when v1.8 is released. This SDK has no
diff --git a/spec/TestClient.ts b/spec/TestClient.ts
index 0a3d25425e3..7d23cadfffa 100644
--- a/spec/TestClient.ts
+++ b/spec/TestClient.ts
@@ -90,7 +90,7 @@ export class TestClient implements IE2EKeyReceiver, ISyncResponder {
         logger.log(this + ": starting");
         this.httpBackend.when("GET", "/versions").respond(200, {
             // we have tests that rely on support for lazy-loading members
-            versions: ["r0.5.0"],
+            versions: ["v1.1"],
         });
         this.httpBackend.when("GET", "/pushrules").respond(200, {});
         this.httpBackend.when("POST", "/filter").respond(200, { filter_id: "fid" });
diff --git a/spec/integ/crypto/crypto.spec.ts b/spec/integ/crypto/crypto.spec.ts
index 8d2b386c413..fd578084fb6 100644
--- a/spec/integ/crypto/crypto.spec.ts
+++ b/spec/integ/crypto/crypto.spec.ts
@@ -1945,7 +1945,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
                     };
                 };
 
-                for (const path of ["/_matrix/client/r0/keys/upload", "/_matrix/client/v3/keys/upload"]) {
+                for (const path of ["/_matrix/client/v3/keys/upload", "/_matrix/client/v3/keys/upload"]) {
                     fetchMock.post(new URL(path, aliceClient.getHomeserverUrl()).toString(), listener, {
                         // These routes are already defined in the E2EKeyReceiver
                         // We want to overwrite the behaviour of the E2EKeyReceiver
@@ -2082,9 +2082,10 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
                     return queryResponseBody;
                 };
 
-                for (const path of ["/_matrix/client/r0/keys/query", "/_matrix/client/v3/keys/query"]) {
-                    fetchMock.post(new URL(path, aliceClient.getHomeserverUrl()).toString(), listener);
-                }
+                fetchMock.post(
+                    new URL("/_matrix/client/v3/keys/query", aliceClient.getHomeserverUrl()).toString(),
+                    listener,
+                );
             });
         }
 
@@ -2175,7 +2176,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
         });
 
         /**
-         * Create a mock to respond to the PUT request `/_matrix/client/r0/user/:userId/account_data/:type(m.secret_storage.*)`
+         * Create a mock to respond to the PUT request `/_matrix/client/v3/user/:userId/account_data/:type(m.secret_storage.*)`
          * Resolved when a key is uploaded (ie in `body.content.key`)
          * https://spec.matrix.org/v1.6/client-server-api/#put_matrixclientv3useruseridaccount_datatype
          */
@@ -2184,7 +2185,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
                 // This url is called multiple times during the secret storage bootstrap process
                 // When we received the newly generated key, we return it
                 fetchMock.put(
-                    "express:/_matrix/client/r0/user/:userId/account_data/:type(m.secret_storage.*)",
+                    "express:/_matrix/client/v3/user/:userId/account_data/:type(m.secret_storage.*)",
                     (url: string, options: RequestInit) => {
                         const content = JSON.parse(options.body as string);
 
@@ -2200,7 +2201,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
         }
 
         /**
-         * Create a mock to respond to the PUT request `/_matrix/client/r0/user/:userId/account_data/m.cross_signing.${key}`
+         * Create a mock to respond to the PUT request `/_matrix/client/v3/user/:userId/account_data/m.cross_signing.${key}`
          * Resolved when the cross signing key is uploaded
          * https://spec.matrix.org/v1.6/client-server-api/#put_matrixclientv3useruseridaccount_datatype
          */
@@ -2208,7 +2209,7 @@ describe.each(Object.entries(CRYPTO_BACKENDS))("crypto (%s)", (backend: string,
             return new Promise((resolve) => {
                 // Called when the cross signing key is uploaded
                 fetchMock.put(
-                    `express:/_matrix/client/r0/user/:userId/account_data/m.cross_signing.${key}`,
+                    `express:/_matrix/client/v3/user/:userId/account_data/m.cross_signing.${key}`,
                     (url: string, options: RequestInit) => {
                         const content = JSON.parse(options.body as string);
                         resolve(content.encrypted);
diff --git a/spec/integ/matrix-client-event-timeline.spec.ts b/spec/integ/matrix-client-event-timeline.spec.ts
index 26e968d7154..0d519cbc596 100644
--- a/spec/integ/matrix-client-event-timeline.spec.ts
+++ b/spec/integ/matrix-client-event-timeline.spec.ts
@@ -1342,7 +1342,7 @@ describe("MatrixClient event timelines", function () {
         function respondToContext(event: Partial<IEvent> = THREAD_ROOT): ExpectedHttpRequest {
             const request = httpBackend.when(
                 "GET",
-                encodeUri("/_matrix/client/r0/rooms/$roomId/context/$eventId", {
+                encodeUri("/_matrix/client/v3/rooms/$roomId/context/$eventId", {
                     $roomId: roomId,
                     $eventId: event.event_id!,
                 }),
@@ -1360,7 +1360,7 @@ describe("MatrixClient event timelines", function () {
         function respondToEvent(event: Partial<IEvent> = THREAD_ROOT): ExpectedHttpRequest {
             const request = httpBackend.when(
                 "GET",
-                encodeUri("/_matrix/client/r0/rooms/$roomId/event/$eventId", {
+                encodeUri("/_matrix/client/v3/rooms/$roomId/event/$eventId", {
                     $roomId: roomId,
                     $eventId: event.event_id!,
                 }),
@@ -1371,7 +1371,7 @@ describe("MatrixClient event timelines", function () {
         function respondToMessagesRequest(): ExpectedHttpRequest {
             const request = httpBackend.when(
                 "GET",
-                encodeUri("/_matrix/client/r0/rooms/$roomId/messages", {
+                encodeUri("/_matrix/client/v3/rooms/$roomId/messages", {
                     $roomId: roomId,
                 }),
             );
diff --git a/spec/integ/matrix-client-methods.spec.ts b/spec/integ/matrix-client-methods.spec.ts
index 89f69069a6a..977190abddb 100644
--- a/spec/integ/matrix-client-methods.spec.ts
+++ b/spec/integ/matrix-client-methods.spec.ts
@@ -73,7 +73,7 @@ describe("MatrixClient", function () {
 
         it("should upload the file", function () {
             httpBackend
-                .when("POST", "/_matrix/media/r0/upload")
+                .when("POST", "/_matrix/media/v3/upload")
                 .check(function (req) {
                     expect(req.rawData).toEqual(buf);
                     expect(req.queryParams?.filename).toEqual("hi.txt");
@@ -108,7 +108,7 @@ describe("MatrixClient", function () {
 
         it("should parse errors into a MatrixError", function () {
             httpBackend
-                .when("POST", "/_matrix/media/r0/upload")
+                .when("POST", "/_matrix/media/v3/upload")
                 .check(function (req) {
                     expect(req.rawData).toEqual(buf);
                     // @ts-ignore private property
@@ -708,7 +708,7 @@ describe("MatrixClient", function () {
         const auth = { identifier: 1 };
         it("should pass through an auth dict", function () {
             httpBackend
-                .when("DELETE", "/_matrix/client/r0/devices/my_device")
+                .when("DELETE", "/_matrix/client/v3/devices/my_device")
                 .check(function (req) {
                     expect(req.data).toEqual({ auth: auth });
                 })
@@ -1102,10 +1102,6 @@ describe("MatrixClient", function () {
                 submit_url: "https://foobar.matrix/_matrix/matrix",
             };
 
-            httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-                versions: ["r0.6.0"],
-            });
-
             const prom = client.requestRegisterEmailToken("bob@email", "secret", 1);
             httpBackend
                 .when("POST", "/register/email/requestToken")
@@ -1126,10 +1122,6 @@ describe("MatrixClient", function () {
         it("should supply an id_access_token", async () => {
             const targetEmail = "gerald@example.org";
 
-            httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-                versions: ["r0.6.0"],
-            });
-
             httpBackend
                 .when("POST", "/invite")
                 .check((req) => {
@@ -1165,10 +1157,6 @@ describe("MatrixClient", function () {
                 ],
             };
 
-            httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-                versions: ["r0.6.0"],
-            });
-
             httpBackend
                 .when("POST", "/createRoom")
                 .check((req) => {
@@ -1652,6 +1640,82 @@ describe("MatrixClient", function () {
             ]);
         });
     });
+
+    describe("getFallbackAuthUrl", () => {
+        it("should return fallback url", () => {
+            expect(client.getFallbackAuthUrl("loginType", "authSessionId")).toMatchInlineSnapshot(
+                `"http://alice.localhost.test.server/_matrix/client/v3/auth/loginType/fallback/web?session=authSessionId"`,
+            );
+        });
+    });
+
+    describe("addThreePidOnly", () => {
+        it("should make expected POST request", async () => {
+            httpBackend
+                .when("POST", "/_matrix/client/v3/account/3pid/add")
+                .check(function (req) {
+                    expect(req.data).toEqual({
+                        client_secret: "secret",
+                        sid: "sid",
+                    });
+                    expect(req.headers["Authorization"]).toBe("Bearer " + accessToken);
+                })
+                .respond(200, {});
+
+            await Promise.all([
+                client.addThreePidOnly({
+                    client_secret: "secret",
+                    sid: "sid",
+                }),
+                httpBackend.flushAllExpected(),
+            ]);
+        });
+    });
+
+    describe("bindThreePid", () => {
+        it("should make expected POST request", async () => {
+            httpBackend
+                .when("POST", "/_matrix/client/v3/account/3pid/bind")
+                .check(function (req) {
+                    expect(req.data).toEqual({
+                        client_secret: "secret",
+                        id_server: "server",
+                        id_access_token: "token",
+                        sid: "sid",
+                    });
+                    expect(req.headers["Authorization"]).toBe("Bearer " + accessToken);
+                })
+                .respond(200, {});
+
+            await Promise.all([
+                client.bindThreePid({
+                    client_secret: "secret",
+                    id_server: "server",
+                    id_access_token: "token",
+                    sid: "sid",
+                }),
+                httpBackend.flushAllExpected(),
+            ]);
+        });
+    });
+
+    describe("unbindThreePid", () => {
+        it("should make expected POST request", async () => {
+            httpBackend
+                .when("POST", "/_matrix/client/v3/account/3pid/unbind")
+                .check(function (req) {
+                    expect(req.data).toEqual({
+                        medium: "email",
+                        address: "alice@server.com",
+                        id_server: "identity.localhost",
+                    });
+                    expect(req.headers["Authorization"]).toBe("Bearer " + accessToken);
+                })
+                .respond(200, {});
+
+            await Promise.all([client.unbindThreePid("email", "alice@server.com"), httpBackend.flushAllExpected()]);
+        });
+    });
 });
 
 function withThreadId(event: MatrixEvent, newThreadId: string): MatrixEvent {
diff --git a/spec/integ/matrix-client-syncing.spec.ts b/spec/integ/matrix-client-syncing.spec.ts
index 45b6f42b4a6..cea06d10d87 100644
--- a/spec/integ/matrix-client-syncing.spec.ts
+++ b/spec/integ/matrix-client-syncing.spec.ts
@@ -224,8 +224,6 @@ describe("MatrixClient syncing", () => {
         });
 
         it("should honour lazyLoadMembers if user is not a guest", () => {
-            client!.doesServerSupportLazyLoading = jest.fn().mockResolvedValue(true);
-
             httpBackend!
                 .when("GET", "/sync")
                 .check((req) => {
@@ -242,8 +240,6 @@ describe("MatrixClient syncing", () => {
         it("should not honour lazyLoadMembers if user is a guest", () => {
             httpBackend!.expectedRequests = [];
             httpBackend!.when("GET", "/versions").respond(200, {});
-            client!.doesServerSupportLazyLoading = jest.fn().mockResolvedValue(true);
-
             httpBackend!
                 .when("GET", "/sync")
                 .check((req) => {
diff --git a/spec/integ/sliding-sync-sdk.spec.ts b/spec/integ/sliding-sync-sdk.spec.ts
index a55316b5fa5..4785ca73b9c 100644
--- a/spec/integ/sliding-sync-sdk.spec.ts
+++ b/spec/integ/sliding-sync-sdk.spec.ts
@@ -121,7 +121,7 @@ describe("SlidingSyncSdk", () => {
             await client!.initCrypto();
             syncOpts.cryptoCallbacks = syncOpts.crypto = client!.crypto;
         }
-        httpBackend!.when("GET", "/_matrix/client/r0/pushrules").respond(200, {});
+        httpBackend!.when("GET", "/_matrix/client/v3/pushrules").respond(200, {});
         sdk = new SlidingSyncSdk(mockSlidingSync, client, testOpts, syncOpts);
     };
 
diff --git a/spec/test-utils/E2EKeyReceiver.ts b/spec/test-utils/E2EKeyReceiver.ts
index 44a863e8b07..24af06d6e37 100644
--- a/spec/test-utils/E2EKeyReceiver.ts
+++ b/spec/test-utils/E2EKeyReceiver.ts
@@ -75,8 +75,6 @@ export class E2EKeyReceiver implements IE2EKeyReceiver {
             const listener = (url: string, options: RequestInit) =>
                 this.onKeyUploadRequest(resolveOneTimeKeys, options);
 
-            // catch both r0 and v3 variants
-            fetchMock.post(new URL("/_matrix/client/r0/keys/upload", homeserverUrl).toString(), listener);
             fetchMock.post(new URL("/_matrix/client/v3/keys/upload", homeserverUrl).toString(), listener);
         });
     }
diff --git a/spec/test-utils/E2EKeyResponder.ts b/spec/test-utils/E2EKeyResponder.ts
index e779e8c5e87..57152f17621 100644
--- a/spec/test-utils/E2EKeyResponder.ts
+++ b/spec/test-utils/E2EKeyResponder.ts
@@ -43,8 +43,6 @@ export class E2EKeyResponder {
     public constructor(homeserverUrl: string) {
         // set up a listener for /keys/query.
         const listener = (url: string, options: RequestInit) => this.onKeyQueryRequest(options);
-        // catch both r0 and v3 variants
-        fetchMock.post(new URL("/_matrix/client/r0/keys/query", homeserverUrl).toString(), listener);
         fetchMock.post(new URL("/_matrix/client/v3/keys/query", homeserverUrl).toString(), listener);
     }
 
diff --git a/spec/test-utils/SyncResponder.ts b/spec/test-utils/SyncResponder.ts
index 56a9c30c8ac..31fae7147a8 100644
--- a/spec/test-utils/SyncResponder.ts
+++ b/spec/test-utils/SyncResponder.ts
@@ -75,7 +75,7 @@ export class SyncResponder implements ISyncResponder {
      */
     public constructor(homeserverUrl: string) {
         this.debug = debugFunc(`sync-responder:[${homeserverUrl}]`);
-        fetchMock.get("begin:" + new URL("/_matrix/client/r0/sync?", homeserverUrl).toString(), (_url, _options) =>
+        fetchMock.get("begin:" + new URL("/_matrix/client/v3/sync?", homeserverUrl).toString(), (_url, _options) =>
             this.onSyncRequest(),
         );
     }
diff --git a/spec/test-utils/client.ts b/spec/test-utils/client.ts
index 1e8a4643893..8123d0d65e6 100644
--- a/spec/test-utils/client.ts
+++ b/spec/test-utils/client.ts
@@ -86,7 +86,6 @@ export const mockClientMethodsEvents = () => ({
  * Returns basic mocked client methods related to server support
  */
 export const mockClientMethodsServer = (): Partial<Record<MethodLikeKeys<MatrixClient>, unknown>> => ({
-    doesServerSupportSeparateAddAndBind: jest.fn(),
     getIdentityServerUrl: jest.fn(),
     getHomeserverUrl: jest.fn(),
     getCapabilities: jest.fn().mockReturnValue({}),
diff --git a/spec/test-utils/mockEndpoints.ts b/spec/test-utils/mockEndpoints.ts
index 386b7a4cb00..4fdcc5b1a81 100644
--- a/spec/test-utils/mockEndpoints.ts
+++ b/spec/test-utils/mockEndpoints.ts
@@ -22,9 +22,9 @@ import fetchMock from "fetch-mock-jest";
  * @param homeserverUrl - the homeserver url for the client under test
  */
 export function mockInitialApiRequests(homeserverUrl: string) {
-    fetchMock.getOnce(new URL("/_matrix/client/versions", homeserverUrl).toString(), { versions: ["r0.5.0"] });
-    fetchMock.getOnce(new URL("/_matrix/client/r0/pushrules/", homeserverUrl).toString(), {});
-    fetchMock.postOnce(new URL("/_matrix/client/r0/user/%40alice%3Alocalhost/filter", homeserverUrl).toString(), {
+    fetchMock.getOnce(new URL("/_matrix/client/versions", homeserverUrl).toString(), { versions: ["v1.1"] });
+    fetchMock.getOnce(new URL("/_matrix/client/v3/pushrules/", homeserverUrl).toString(), {});
+    fetchMock.postOnce(new URL("/_matrix/client/v3/user/%40alice%3Alocalhost/filter", homeserverUrl).toString(), {
         filter_id: "fid",
     });
 }
@@ -32,13 +32,13 @@ export function mockInitialApiRequests(homeserverUrl: string) {
 /**
  * Mock the requests needed to set up cross signing
  *
- * Return 404 error for `GET _matrix/client/r0/user/:userId/account_data/:type` request
+ * Return 404 error for `GET _matrix/client/v3/user/:userId/account_data/:type` request
  * Return `{}` for `POST _matrix/client/v3/keys/signatures/upload` request (named `upload-sigs` for fetchMock check)
  * Return `{}` for `POST /_matrix/client/(unstable|v3)/keys/device_signing/upload` request (named `upload-keys` for fetchMock check)
  */
 export function mockSetupCrossSigningRequests(): void {
     // have account_data requests return an empty object
-    fetchMock.get("express:/_matrix/client/r0/user/:userId/account_data/:type", {
+    fetchMock.get("express:/_matrix/client/v3/user/:userId/account_data/:type", {
         status: 404,
         body: { errcode: "M_NOT_FOUND", error: "Account data not found." },
     });
diff --git a/spec/unit/autodiscovery.spec.ts b/spec/unit/autodiscovery.spec.ts
index 2ffe9be1a68..b7614d7240f 100644
--- a/spec/unit/autodiscovery.spec.ts
+++ b/spec/unit/autodiscovery.spec.ts
@@ -18,7 +18,7 @@ limitations under the License.
 import fetchMock from "fetch-mock-jest";
 import MockHttpBackend from "matrix-mock-request";
 
-import { M_AUTHENTICATION } from "../../src";
+import { AutoDiscoveryAction, M_AUTHENTICATION } from "../../src";
 import { AutoDiscovery } from "../../src/autodiscovery";
 import { OidcError } from "../../src/oidc/error";
 import { makeDelegatedAuthConfig } from "../test-utils/oidc";
@@ -351,7 +351,7 @@ describe("AutoDiscovery", function () {
         function () {
             const httpBackend = getHttpBackend();
             httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-                not_matrix_versions: ["r0.0.1"],
+                not_matrix_versions: ["v1.1"],
             });
             httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
                 "m.homeserver": {
@@ -388,7 +388,7 @@ describe("AutoDiscovery", function () {
                 expect(req.path).toEqual("https://example.org/_matrix/client/versions");
             })
             .respond(200, {
-                versions: ["r0.0.1"],
+                versions: ["v1.1"],
             });
         httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
             "m.homeserver": {
@@ -428,7 +428,7 @@ describe("AutoDiscovery", function () {
                 expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
             })
             .respond(200, {
-                versions: ["r0.0.1"],
+                versions: ["v1.1"],
             });
         httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
             "m.homeserver": {
@@ -469,7 +469,7 @@ describe("AutoDiscovery", function () {
                 expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
             })
             .respond(200, {
-                versions: ["r0.0.1"],
+                versions: ["v1.1"],
             });
         httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
             "m.homeserver": {
@@ -515,7 +515,7 @@ describe("AutoDiscovery", function () {
                     expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
                 })
                 .respond(200, {
-                    versions: ["r0.0.1"],
+                    versions: ["v1.1"],
                 });
             httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
                 "m.homeserver": {
@@ -560,7 +560,7 @@ describe("AutoDiscovery", function () {
                     expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
                 })
                 .respond(200, {
-                    versions: ["r0.0.1"],
+                    versions: ["v1.1"],
                 });
             httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
                 "m.homeserver": {
@@ -606,7 +606,7 @@ describe("AutoDiscovery", function () {
                     expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
                 })
                 .respond(200, {
-                    versions: ["r0.0.1"],
+                    versions: ["v1.1"],
                 });
             httpBackend.when("GET", "/_matrix/identity/v2").respond(404, {});
             httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
@@ -653,7 +653,7 @@ describe("AutoDiscovery", function () {
                     expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
                 })
                 .respond(200, {
-                    versions: ["r0.0.1"],
+                    versions: ["v1.1"],
                 });
             httpBackend.when("GET", "/_matrix/identity/v2").respond(500, {});
             httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
@@ -697,7 +697,7 @@ describe("AutoDiscovery", function () {
                 expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
             })
             .respond(200, {
-                versions: ["r0.0.1"],
+                versions: ["v1.1"],
             });
         httpBackend
             .when("GET", "/_matrix/identity/v2")
@@ -747,7 +747,7 @@ describe("AutoDiscovery", function () {
                 expect(req.path).toEqual("https://chat.example.org/_matrix/client/versions");
             })
             .respond(200, {
-                versions: ["r0.0.1"],
+                versions: ["v1.1"],
             });
         httpBackend
             .when("GET", "/_matrix/identity/v2")
@@ -867,6 +867,37 @@ describe("AutoDiscovery", function () {
         ]);
     });
 
+    it("should FAIL_ERROR for unsupported Matrix version", () => {
+        const httpBackend = getHttpBackend();
+        httpBackend.when("GET", "/.well-known/matrix/client").respond(200, {
+            "m.homeserver": {
+                base_url: "https://example.org",
+            },
+        });
+        httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
+            versions: ["r0.6.0"],
+        });
+        return Promise.all([
+            httpBackend.flushAllExpected(),
+            AutoDiscovery.findClientConfig("example.org").then((conf) => {
+                const expected = {
+                    "m.homeserver": {
+                        state: AutoDiscoveryAction.FAIL_ERROR,
+                        error: AutoDiscovery.ERROR_HOMESERVER_TOO_OLD,
+                        base_url: "https://example.org",
+                    },
+                    "m.identity_server": {
+                        state: "PROMPT",
+                        error: null,
+                        base_url: null,
+                    },
+                };
+
+                expect(conf).toEqual(expected);
+            }),
+        ]);
+    });
+
     describe("m.authentication", () => {
         const homeserverName = "example.org";
         const homeserverUrl = "https://chat.example.org/";
@@ -879,7 +910,7 @@ describe("AutoDiscovery", function () {
 
         beforeEach(() => {
             fetchMock.resetBehavior();
-            fetchMock.get(`${homeserverUrl}_matrix/client/versions`, { versions: ["r0.0.1"] });
+            fetchMock.get(`${homeserverUrl}_matrix/client/versions`, { versions: ["v1.1"] });
 
             fetchMock.get("https://example.org/.well-known/matrix/client", {
                 "m.homeserver": {
diff --git a/spec/unit/content-repo.spec.ts b/spec/unit/content-repo.spec.ts
index 2cbd361239e..91953945ac7 100644
--- a/spec/unit/content-repo.spec.ts
+++ b/spec/unit/content-repo.spec.ts
@@ -33,7 +33,7 @@ describe("ContentRepo", function () {
         it("should return a download URL if no width/height/resize are specified", function () {
             const mxcUri = "mxc://server.name/resourceid";
             expect(getHttpUriForMxc(baseUrl, mxcUri)).toEqual(
-                baseUrl + "/_matrix/media/r0/download/server.name/resourceid",
+                baseUrl + "/_matrix/media/v3/download/server.name/resourceid",
             );
         });
 
@@ -44,21 +44,21 @@ describe("ContentRepo", function () {
         it("should return a thumbnail URL if a width/height/resize is specified", function () {
             const mxcUri = "mxc://server.name/resourceid";
             expect(getHttpUriForMxc(baseUrl, mxcUri, 32, 64, "crop")).toEqual(
-                baseUrl + "/_matrix/media/r0/thumbnail/server.name/resourceid" + "?width=32&height=64&method=crop",
+                baseUrl + "/_matrix/media/v3/thumbnail/server.name/resourceid" + "?width=32&height=64&method=crop",
             );
         });
 
         it("should put fragments from mxc:// URIs after any query parameters", function () {
             const mxcUri = "mxc://server.name/resourceid#automade";
             expect(getHttpUriForMxc(baseUrl, mxcUri, 32)).toEqual(
-                baseUrl + "/_matrix/media/r0/thumbnail/server.name/resourceid" + "?width=32#automade",
+                baseUrl + "/_matrix/media/v3/thumbnail/server.name/resourceid" + "?width=32#automade",
             );
         });
 
         it("should put fragments from mxc:// URIs at the end of the HTTP URI", function () {
             const mxcUri = "mxc://server.name/resourceid#automade";
             expect(getHttpUriForMxc(baseUrl, mxcUri)).toEqual(
-                baseUrl + "/_matrix/media/r0/download/server.name/resourceid#automade",
+                baseUrl + "/_matrix/media/v3/download/server.name/resourceid#automade",
             );
         });
     });
diff --git a/spec/unit/http-api/__snapshots__/index.spec.ts.snap b/spec/unit/http-api/__snapshots__/index.spec.ts.snap
index e6487ddeb0f..f60866aa238 100644
--- a/spec/unit/http-api/__snapshots__/index.spec.ts.snap
+++ b/spec/unit/http-api/__snapshots__/index.spec.ts.snap
@@ -6,6 +6,6 @@ exports[`MatrixHttpApi should return expected object from \`getContentUri\` 1`]
   "params": {
     "access_token": "token",
   },
-  "path": "/_matrix/media/r0/upload",
+  "path": "/_matrix/media/v3/upload",
 }
 `;
diff --git a/spec/unit/http-api/index.spec.ts b/spec/unit/http-api/index.spec.ts
index cbaa15aa417..668417ea9eb 100644
--- a/spec/unit/http-api/index.spec.ts
+++ b/spec/unit/http-api/index.spec.ts
@@ -84,7 +84,7 @@ describe("MatrixHttpApi", () => {
         upload = api.uploadContent({} as File);
         expect(xhr.open).toHaveBeenCalledWith(
             Method.Post,
-            baseUrl.toLowerCase() + "/_matrix/media/r0/upload?access_token=token",
+            baseUrl.toLowerCase() + "/_matrix/media/v3/upload?access_token=token",
         );
         expect(xhr.setRequestHeader).not.toHaveBeenCalledWith("Authorization");
     });
@@ -96,7 +96,7 @@ describe("MatrixHttpApi", () => {
             accessToken: "token",
         });
         upload = api.uploadContent({} as File);
-        expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/r0/upload");
+        expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/v3/upload");
         expect(xhr.setRequestHeader).toHaveBeenCalledWith("Authorization", "Bearer token");
     });
 
@@ -105,14 +105,14 @@ describe("MatrixHttpApi", () => {
         upload = api.uploadContent({} as File, { name: "name" });
         expect(xhr.open).toHaveBeenCalledWith(
             Method.Post,
-            baseUrl.toLowerCase() + "/_matrix/media/r0/upload?filename=name",
+            baseUrl.toLowerCase() + "/_matrix/media/v3/upload?filename=name",
         );
     });
 
     it("should allow not sending the filename", () => {
         const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
         upload = api.uploadContent({} as File, { name: "name", includeFilename: false });
-        expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/r0/upload");
+        expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/v3/upload");
     });
 
     it("should abort xhr when the upload is aborted", () => {
diff --git a/spec/unit/matrix-client.spec.ts b/spec/unit/matrix-client.spec.ts
index 404f7fcd7fc..d90d3c9ed03 100644
--- a/spec/unit/matrix-client.spec.ts
+++ b/spec/unit/matrix-client.spec.ts
@@ -201,7 +201,7 @@ describe("MatrixClient", function () {
         if (path === KEEP_ALIVE_PATH && acceptKeepalives) {
             return Promise.resolve({
                 unstable_features: unstableFeatures,
-                versions: ["r0.6.0", "r0.6.1"],
+                versions: ["v1.1"],
             });
         }
         const next = httpLookups.shift();
diff --git a/spec/unit/queueToDevice.spec.ts b/spec/unit/queueToDevice.spec.ts
index c09d6968703..1099bcb82e8 100644
--- a/spec/unit/queueToDevice.spec.ts
+++ b/spec/unit/queueToDevice.spec.ts
@@ -195,7 +195,7 @@ describe.each([[StoreType.Memory], [StoreType.IndexedDB]])("queueToDevice (%s st
 
     it("retries on retryImmediately()", async function () {
         httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-            versions: ["r0.0.1"],
+            versions: ["v1.1"],
         });
 
         await Promise.all([client.startClient(), httpBackend.flush(undefined, 1, 20)]);
@@ -219,7 +219,7 @@ describe.each([[StoreType.Memory], [StoreType.IndexedDB]])("queueToDevice (%s st
 
     it("retries on when client is started", async function () {
         httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-            versions: ["r0.0.1"],
+            versions: ["v1.1"],
         });
 
         await Promise.all([client.startClient(), httpBackend.flush("/_matrix/client/versions", 1, 20)]);
@@ -243,7 +243,7 @@ describe.each([[StoreType.Memory], [StoreType.IndexedDB]])("queueToDevice (%s st
 
     it("retries when a message is retried", async function () {
         httpBackend.when("GET", "/_matrix/client/versions").respond(200, {
-            versions: ["r0.0.1"],
+            versions: ["v1.1"],
         });
 
         await Promise.all([client.startClient(), httpBackend.flush(undefined, 1, 20)]);
diff --git a/src/@types/requests.ts b/src/@types/requests.ts
index bfab7fa0145..e67fb873b76 100644
--- a/src/@types/requests.ts
+++ b/src/@types/requests.ts
@@ -193,12 +193,6 @@ export interface IBindThreePidBody {
     sid: string;
 }
 
-export interface IAddThreePidBody {
-    client_secret: string;
-    id_server: string;
-    sid: string;
-}
-
 export interface IRelationsRequestOpts {
     from?: string;
     to?: string;
diff --git a/src/autodiscovery.ts b/src/autodiscovery.ts
index b7a16f10702..a1ce6c09ab9 100644
--- a/src/autodiscovery.ts
+++ b/src/autodiscovery.ts
@@ -28,6 +28,7 @@ import {
     validateWellKnownAuthentication,
 } from "./oidc/validate";
 import { OidcError } from "./oidc/error";
+import { MINIMUM_MATRIX_VERSION } from "./version-support";
 
 // Dev note: Auto discovery is part of the spec.
 // See: https://matrix.org/docs/spec/client_server/r0.4.0.html#server-discovery
@@ -50,6 +51,9 @@ enum AutoDiscoveryError {
     InvalidIs = "Invalid identity server discovery response",
     MissingWellknown = "No .well-known JSON file found",
     InvalidJson = "Invalid JSON",
+    HomeserverTooOld = "The homeserver does not meet the minimum version requirements",
+    // 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",
 }
 
 interface AutoDiscoveryState {
@@ -108,6 +112,8 @@ export class AutoDiscovery {
 
     public static readonly ERROR_INVALID_JSON = AutoDiscoveryError.InvalidJson;
 
+    public static readonly ERROR_HOMESERVER_TOO_OLD = AutoDiscoveryError.HomeserverTooOld;
+
     public static readonly ALL_ERRORS = Object.keys(AutoDiscoveryError);
 
     /**
@@ -199,7 +205,7 @@ export class AutoDiscovery {
 
         // Step 3: Make sure the homeserver URL points to a homeserver.
         const hsVersions = await this.fetchWellKnownObject<IServerVersions>(`${hsUrl}/_matrix/client/versions`);
-        if (!hsVersions?.raw?.["versions"]) {
+        if (!hsVersions || !Array.isArray(hsVersions.raw?.["versions"])) {
             logger.error("Invalid /versions response");
             clientConfig["m.homeserver"].error = AutoDiscovery.ERROR_INVALID_HOMESERVER;
 
@@ -210,6 +216,18 @@ export class AutoDiscovery {
             return Promise.resolve(clientConfig);
         }
 
+        // Step 3.1: Non-spec check to ensure the server will actually work for us
+        if (!hsVersions.raw!["versions"].includes(MINIMUM_MATRIX_VERSION)) {
+            logger.error("Homeserver does not meet minimum version requirements");
+            clientConfig["m.homeserver"].error = AutoDiscovery.ERROR_HOMESERVER_TOO_OLD;
+
+            // Supply the base_url to the caller because they may be ignoring liveliness
+            // errors, like this one.
+            clientConfig["m.homeserver"].base_url = hsUrl;
+
+            return Promise.resolve(clientConfig);
+        }
+
         // Step 4: Now that the homeserver looks valid, update our client config.
         clientConfig["m.homeserver"] = {
             state: AutoDiscovery.SUCCESS,
diff --git a/src/client.ts b/src/client.ts
index 750382a3b03..6b6fe2c227b 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -133,7 +133,6 @@ import {
     IFilterResponse,
     ITagsResponse,
     IStatusResponse,
-    IAddThreePidBody,
     KnockRoomOpts,
 } from "./@types/requests";
 import {
@@ -1287,7 +1286,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             baseUrl: opts.baseUrl,
             idBaseUrl: opts.idBaseUrl,
             accessToken: opts.accessToken,
-            prefix: ClientPrefix.R0,
+            prefix: ClientPrefix.V3,
             onlyData: true,
             extraParams: opts.queryParams,
             localTimeoutMs: opts.localTimeoutMs,
@@ -3430,9 +3429,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             await this.crypto.crossSigningInfo.signObject(data.auth_data, "master");
         }
 
-        const res = await this.http.authedRequest<IKeyBackupInfo>(Method.Post, "/room_keys/version", undefined, data, {
-            prefix: ClientPrefix.V3,
-        });
+        const res = await this.http.authedRequest<IKeyBackupInfo>(Method.Post, "/room_keys/version", undefined, data);
 
         // We could assume everything's okay and enable directly, but this ensures
         // we run the same signature verification that will be used for future
@@ -3929,7 +3926,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      */
     public getMediaConfig(): Promise<IMediaConfig> {
         return this.http.authedRequest(Method.Get, "/config", undefined, undefined, {
-            prefix: MediaPrefix.R0,
+            prefix: MediaPrefix.V3,
         });
     }
 
@@ -5184,7 +5181,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             },
             undefined,
             {
-                prefix: MediaPrefix.R0,
+                prefix: MediaPrefix.V3,
                 priority: "low",
             },
         );
@@ -5351,7 +5348,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             address: address,
         };
 
-        if (this.identityServer?.getAccessToken && (await this.doesServerAcceptIdentityAccessToken())) {
+        if (this.identityServer?.getAccessToken) {
             const identityAccessToken = await this.identityServer.getAccessToken();
             if (identityAccessToken) {
                 params["id_access_token"] = identityAccessToken;
@@ -6143,7 +6140,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         const opts = {
             prefix:
                 Thread.hasServerSideListSupport === FeatureSupport.Stable
-                    ? "/_matrix/client/v1"
+                    ? ClientPrefix.V1
                     : "/_matrix/client/unstable/org.matrix.msc3856",
         };
 
@@ -6669,20 +6666,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     ): Promise<T> {
         const postParams = Object.assign({}, params);
 
-        // If the HS supports separate add and bind, then requestToken endpoints
-        // don't need an IS as they are all validated by the HS directly.
-        if (!(await this.doesServerSupportSeparateAddAndBind()) && this.idBaseUrl) {
-            const idServerUrl = new URL(this.idBaseUrl);
-            postParams.id_server = idServerUrl.host;
-
-            if (this.identityServer?.getAccessToken && (await this.doesServerAcceptIdentityAccessToken())) {
-                const identityAccessToken = await this.identityServer.getAccessToken();
-                if (identityAccessToken) {
-                    postParams.id_access_token = identityAccessToken;
-                }
-            }
-        }
-
         return this.http.request(Method.Post, endpoint, undefined, postParams);
     }
 
@@ -7387,78 +7370,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return versions && versions.includes(version);
     }
 
-    /**
-     * Query the server to see if it supports members lazy loading
-     * @returns true if server supports lazy loading
-     */
-    public async doesServerSupportLazyLoading(): Promise<boolean> {
-        const response = await this.getVersions();
-        if (!response) return false;
-
-        const versions = response["versions"];
-        const unstableFeatures = response["unstable_features"];
-
-        return (
-            (versions && versions.includes("r0.5.0")) || (unstableFeatures && unstableFeatures["m.lazy_load_members"])
-        );
-    }
-
-    /**
-     * Query the server to see if the `id_server` parameter is required
-     * when registering with an 3pid, adding a 3pid or resetting password.
-     * @returns true if id_server parameter is required
-     */
-    public async doesServerRequireIdServerParam(): Promise<boolean> {
-        const response = await this.getVersions();
-        if (!response) return true;
-
-        const versions = response["versions"];
-
-        // Supporting r0.6.0 is the same as having the flag set to false
-        if (versions && versions.includes("r0.6.0")) {
-            return false;
-        }
-
-        const unstableFeatures = response["unstable_features"];
-        if (!unstableFeatures) return true;
-        if (unstableFeatures["m.require_identity_server"] === undefined) {
-            return true;
-        } else {
-            return unstableFeatures["m.require_identity_server"];
-        }
-    }
-
-    /**
-     * Query the server to see if the `id_access_token` parameter can be safely
-     * passed to the homeserver. Some homeservers may trigger errors if they are not
-     * prepared for the new parameter.
-     * @returns true if id_access_token can be sent
-     */
-    public async doesServerAcceptIdentityAccessToken(): Promise<boolean> {
-        const response = await this.getVersions();
-        if (!response) return false;
-
-        const versions = response["versions"];
-        const unstableFeatures = response["unstable_features"];
-        return (versions && versions.includes("r0.6.0")) || (unstableFeatures && unstableFeatures["m.id_access_token"]);
-    }
-
-    /**
-     * Query the server to see if it supports separate 3PID add and bind functions.
-     * This affects the sequence of API calls clients should use for these operations,
-     * so it's helpful to be able to check for support.
-     * @returns true if separate functions are supported
-     */
-    public async doesServerSupportSeparateAddAndBind(): Promise<boolean> {
-        const response = await this.getVersions();
-        if (!response) return false;
-
-        const versions = response["versions"];
-        const unstableFeatures = response["unstable_features"];
-
-        return versions?.includes("r0.6.0") || unstableFeatures?.["m.separate_add_and_bind"];
-    }
-
     /**
      * Query the server to see if it lists support for an unstable feature
      * in the /versions response
@@ -7530,14 +7441,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         }
     }
 
-    /**
-     * Query the server to see if it supports the MSC2457 `logout_devices` parameter when setting password
-     * @returns true if server supports the `logout_devices` parameter
-     */
-    public doesServerSupportLogoutDevices(): Promise<boolean> {
-        return this.isVersionSupported("r0.6.1");
-    }
-
     /**
      * Get if lazy loading members is being used.
      * @returns Whether or not members are lazy loaded by this client
@@ -7922,18 +7825,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         });
     }
 
-    /**
-     * @param relayState - URL Callback after SAML2 Authentication
-     * @returns Promise which resolves to a LoginResponse object
-     * @returns Rejects: with an error response.
-     * @deprecated this isn't in the Matrix spec anymore
-     */
-    public loginWithSAML2(relayState: string): Promise<LoginResponse> {
-        return this.login("m.login.saml2", {
-            relay_state: relayState,
-        });
-    }
-
     /**
      * @param redirectUrl - The URL to redirect to after the HS
      * authenticates with CAS.
@@ -7963,7 +7854,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             [SSO_ACTION_PARAM.unstable!]: action,
         };
 
-        return this.http.getUrl(url, params, ClientPrefix.R0).href;
+        return this.http.getUrl(url, params).href;
     }
 
     /**
@@ -8081,13 +7972,9 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             $loginType: loginType,
         });
 
-        return this.http.getUrl(
-            path,
-            {
-                session: authSessionId,
-            },
-            ClientPrefix.R0,
-        ).href;
+        return this.http.getUrl(path, {
+            session: authSessionId,
+        }).href;
     }
 
     /**
@@ -8102,11 +7989,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
 
         // inject the id_access_token if inviting 3rd party addresses
         const invitesNeedingToken = (options.invite_3pid || []).filter((i) => !i.id_access_token);
-        if (
-            invitesNeedingToken.length > 0 &&
-            this.identityServer?.getAccessToken &&
-            (await this.doesServerAcceptIdentityAccessToken())
-        ) {
+        if (invitesNeedingToken.length > 0 && this.identityServer?.getAccessToken) {
             const identityAccessToken = await this.identityServer.getAccessToken();
             if (identityAccessToken) {
                 for (const invite of invitesNeedingToken) {
@@ -8465,30 +8348,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.http.authedRequest(Method.Put, path, undefined, { visibility });
     }
 
-    /**
-     * Set the visbility of a room bridged to a 3rd party network in
-     * the current HS's room directory.
-     * @param networkId - the network ID of the 3rd party
-     *                 instance under which this room is published under.
-     * @param visibility - "public" to make the room visible
-     *                 in the public directory, or "private" to make
-     *                 it invisible.
-     * @returns Promise which resolves: result object
-     * @returns Rejects: with an error response.
-     * @deprecated missing from the spec
-     */
-    public setRoomDirectoryVisibilityAppService(
-        networkId: string,
-        roomId: string,
-        visibility: "public" | "private",
-    ): Promise<any> {
-        const path = utils.encodeUri("/directory/list/appservice/$networkId/$roomId", {
-            $networkId: networkId,
-            $roomId: roomId,
-        });
-        return this.http.authedRequest(Method.Put, path, undefined, { visibility: visibility });
-    }
-
     /**
      * Query the user directory with a term matching user IDs, display names and domains.
      * @param term - the term with which to search.
@@ -8571,31 +8430,10 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
         return this.http.authedRequest(Method.Get, "/account/3pid");
     }
 
-    /**
-     * Add a 3PID to your homeserver account and optionally bind it to an identity
-     * server as well. An identity server is required as part of the `creds` object.
-     *
-     * @deprecated this API is deprecated, and you should instead use `addThreePidOnly` for homeservers that support it.
-     *
-     * @returns Promise which resolves: on success
-     * @returns Rejects: with an error response.
-     */
-    public addThreePid(creds: IAddThreePidBody, bind: boolean): Promise<{ submit_url?: string }> {
-        const path = "/account/3pid";
-        const data = {
-            threePidCreds: creds,
-            bind: bind,
-        };
-        return this.http.authedRequest(Method.Post, path, undefined, data);
-    }
-
     /**
      * Add a 3PID to your homeserver account. This API does not use an identity
      * server, as the homeserver is expected to handle 3PID ownership validation.
      *
-     * You can check whether a homeserver supports this API via
-     * `doesServerSupportSeparateAddAndBind`.
-     *
      * @param data - A object with 3PID validation data from having called
      * `account/3pid/<medium>/requestToken` on the homeserver.
      * @returns Promise which resolves: to an empty object `{}`
@@ -8603,8 +8441,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      */
     public async addThreePidOnly(data: IAddThreePidOnlyBody): Promise<{}> {
         const path = "/account/3pid/add";
-        const prefix = (await this.isVersionSupported("r0.6.0")) ? ClientPrefix.R0 : ClientPrefix.Unstable;
-        return this.http.authedRequest(Method.Post, path, undefined, data, { prefix });
+        return this.http.authedRequest(Method.Post, path, undefined, data);
     }
 
     /**
@@ -8612,9 +8449,6 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      * identity server handles 3PID ownership validation and the homeserver records
      * the new binding to track where all 3PIDs for the account are bound.
      *
-     * You can check whether a homeserver supports this API via
-     * `doesServerSupportSeparateAddAndBind`.
-     *
      * @param data - A object with 3PID validation data from having called
      * `validate/<medium>/requestToken` on the identity server. It should also
      * contain `id_server` and `id_access_token` fields as well.
@@ -8623,8 +8457,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      */
     public async bindThreePid(data: IBindThreePidBody): Promise<{}> {
         const path = "/account/3pid/bind";
-        const prefix = (await this.isVersionSupported("r0.6.0")) ? ClientPrefix.R0 : ClientPrefix.Unstable;
-        return this.http.authedRequest(Method.Post, path, undefined, data, { prefix });
+        return this.http.authedRequest(Method.Post, path, undefined, data);
     }
 
     /**
@@ -8649,8 +8482,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
             address,
             id_server: this.getIdentityServerUrl(true),
         };
-        const prefix = (await this.isVersionSupported("r0.6.0")) ? ClientPrefix.R0 : ClientPrefix.Unstable;
-        return this.http.authedRequest(Method.Post, path, undefined, data, { prefix });
+        return this.http.authedRequest(Method.Post, path, undefined, data);
     }
 
     /**
@@ -8958,9 +8790,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
     }
 
     public uploadKeySignatures(content: KeySignatures): Promise<IUploadKeySignaturesResponse> {
-        return this.http.authedRequest(Method.Post, "/keys/signatures/upload", undefined, content, {
-            prefix: ClientPrefix.V3,
-        });
+        return this.http.authedRequest(Method.Post, "/keys/signatures/upload", undefined, content);
     }
 
     /**
diff --git a/src/content-repo.ts b/src/content-repo.ts
index d3130aa722a..d83ab6dbd29 100644
--- a/src/content-repo.ts
+++ b/src/content-repo.ts
@@ -49,7 +49,7 @@ export function getHttpUriForMxc(
         }
     }
     let serverAndMediaId = mxc.slice(6); // strips mxc://
-    let prefix = "/_matrix/media/r0/download/";
+    let prefix = "/_matrix/media/v3/download/";
     const params: Record<string, string> = {};
 
     if (width) {
@@ -64,7 +64,7 @@ export function getHttpUriForMxc(
     if (Object.keys(params).length > 0) {
         // these are thumbnailing params so they probably want the
         // thumbnailing API...
-        prefix = "/_matrix/media/r0/thumbnail/";
+        prefix = "/_matrix/media/v3/thumbnail/";
     }
 
     const fragmentOffset = serverAndMediaId.indexOf("#");
diff --git a/src/http-api/index.ts b/src/http-api/index.ts
index 1de1f847b27..4f9097665f8 100644
--- a/src/http-api/index.ts
+++ b/src/http-api/index.ts
@@ -110,7 +110,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
                 });
             };
 
-            const url = this.getUrl("/upload", undefined, MediaPrefix.R0);
+            const url = this.getUrl("/upload", undefined, MediaPrefix.V3);
 
             if (includeFilename && fileName) {
                 url.searchParams.set("filename", encodeURIComponent(fileName));
@@ -139,7 +139,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
             const headers: Record<string, string> = { "Content-Type": contentType };
 
             this.authedRequest<UploadResponse>(Method.Post, "/upload", queryParams, file, {
-                prefix: MediaPrefix.R0,
+                prefix: MediaPrefix.V3,
                 headers,
                 abortSignal: abortController.signal,
             })
@@ -182,7 +182,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
     public getContentUri(): IContentUri {
         return {
             base: this.opts.baseUrl,
-            path: MediaPrefix.R0 + "/upload",
+            path: MediaPrefix.V3 + "/upload",
             params: {
                 access_token: this.opts.accessToken!,
             },
diff --git a/src/http-api/prefix.ts b/src/http-api/prefix.ts
index f15b1ac1e77..5eee4672ae1 100644
--- a/src/http-api/prefix.ts
+++ b/src/http-api/prefix.ts
@@ -16,11 +16,7 @@ limitations under the License.
 
 export enum ClientPrefix {
     /**
-     * A constant representing the URI path for release 0 of the Client-Server HTTP API.
-     */
-    R0 = "/_matrix/client/r0",
-    /**
-     * A constant representing the URI path for the legacy release v1 of the Client-Server HTTP API.
+     * A constant representing the URI path for Client-Server API endpoints versioned at v1.
      */
     V1 = "/_matrix/client/v1",
     /**
@@ -42,7 +38,11 @@ export enum IdentityPrefix {
 
 export enum MediaPrefix {
     /**
-     * URI path for the media repo API
+     * A constant representing the URI path for Client-Server API Media endpoints versioned at v1.
+     */
+    V1 = "/_matrix/media/v3",
+    /**
+     * A constant representing the URI path for Client-Server API Media endpoints versioned at v3.
      */
-    R0 = "/_matrix/media/r0",
+    V3 = "/_matrix/media/v3",
 }
diff --git a/src/interactive-auth.ts b/src/interactive-auth.ts
index 3617ce1765f..d2a1fe087ab 100644
--- a/src/interactive-auth.ts
+++ b/src/interactive-auth.ts
@@ -345,10 +345,8 @@ export class InteractiveAuth<T> {
                     sid: this.emailSid,
                     client_secret: this.clientSecret,
                 };
-                if (await this.matrixClient.doesServerRequireIdServerParam()) {
-                    const idServerParsedUrl = new URL(this.matrixClient.getIdentityServerUrl()!);
-                    creds.id_server = idServerParsedUrl.host;
-                }
+                const idServerParsedUrl = new URL(this.matrixClient.getIdentityServerUrl()!);
+                creds.id_server = idServerParsedUrl.host;
                 authDict = {
                     type: EMAIL_STAGE_TYPE,
                     // TODO: Remove `threepid_creds` once servers support proper UIA
diff --git a/src/sync.ts b/src/sync.ts
index f2ec1b32b0f..8e8fde2199c 100644
--- a/src/sync.ts
+++ b/src/sync.ts
@@ -649,18 +649,11 @@ export class SyncApi {
             this.opts.lazyLoadMembers = false;
         }
         if (this.opts.lazyLoadMembers) {
-            debuglog("Checking server lazy load support...");
-            const supported = await this.client.doesServerSupportLazyLoading();
-            if (supported) {
-                debuglog("Enabling lazy load on sync filter...");
-                if (!this.opts.filter) {
-                    this.opts.filter = this.buildDefaultFilter();
-                }
-                this.opts.filter.setLazyLoadMembers(true);
-            } else {
-                debuglog("LL: lazy loading requested but not supported " + "by server, so disabling");
-                this.opts.lazyLoadMembers = false;
+            debuglog("Enabling lazy load on sync filter...");
+            if (!this.opts.filter) {
+                this.opts.filter = this.buildDefaultFilter();
             }
+            this.opts.filter.setLazyLoadMembers(true);
         }
         // need to vape the store when enabling LL and wasn't enabled before
         debuglog("Checking whether lazy loading has changed in store...");
diff --git a/src/version-support.ts b/src/version-support.ts
new file mode 100644
index 00000000000..dd2d55ad9e2
--- /dev/null
+++ b/src/version-support.ts
@@ -0,0 +1,20 @@
+/*
+Copyright 2022 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.
+*/
+
+/**
+ * The minimum Matrix specification version the js-sdk supports.
+ */
+export const MINIMUM_MATRIX_VERSION = "v1.1";