diff --git a/spec/unit/http-api/fetch.spec.ts b/spec/unit/http-api/fetch.spec.ts
index 0e3bed566..b76944031 100644
--- a/spec/unit/http-api/fetch.spec.ts
+++ b/spec/unit/http-api/fetch.spec.ts
@@ -14,8 +14,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 */
 
-import { type Mocked } from "jest-mock";
-
+import type { Mocked, MockedFunction } from "jest-mock";
 import { FetchHttpApi } from "../../../src/http-api/fetch";
 import { TypedEventEmitter } from "../../../src/models/typed-event-emitter";
 import {
@@ -43,8 +42,8 @@ describe("FetchHttpApi", () => {
     });
 
     it("should support aborting multiple times", () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn });
+        const fetchFn = makeMockFetchFn();
+        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn, onlyData: true });
 
         api.request(Method.Get, "/foo");
         api.request(Method.Get, "/baz");
@@ -68,13 +67,13 @@ describe("FetchHttpApi", () => {
     it("should fall back to global fetch if fetchFn not provided", () => {
         globalThis.fetch = jest.fn();
         expect(globalThis.fetch).not.toHaveBeenCalled();
-        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         api.fetch("test");
         expect(globalThis.fetch).toHaveBeenCalled();
     });
 
     it("should update identity server base url", () => {
-        const api = new FetchHttpApi<IHttpOpts>(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new FetchHttpApi<IHttpOpts>(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         expect(api.opts.idBaseUrl).toBeUndefined();
         api.setIdBaseUrl("https://id.foo.bar");
         expect(api.opts.idBaseUrl).toBe("https://id.foo.bar");
@@ -82,23 +81,35 @@ describe("FetchHttpApi", () => {
 
     describe("idServerRequest", () => {
         it("should throw if no idBaseUrl", () => {
-            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
             expect(() => api.idServerRequest(Method.Get, "/test", {}, IdentityPrefix.V2)).toThrow(
                 "No identity server base URL set",
             );
         });
 
         it("should send params as query string for GET requests", () => {
-            const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, idBaseUrl, prefix, fetchFn });
+            const fetchFn = makeMockFetchFn();
+            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
+                baseUrl,
+                idBaseUrl,
+                prefix,
+                fetchFn,
+                onlyData: true,
+            });
             api.idServerRequest(Method.Get, "/test", { foo: "bar", via: ["a", "b"] }, IdentityPrefix.V2);
             expect(fetchFn.mock.calls[0][0].searchParams.get("foo")).toBe("bar");
             expect(fetchFn.mock.calls[0][0].searchParams.getAll("via")).toEqual(["a", "b"]);
         });
 
         it("should send params as body for non-GET requests", () => {
-            const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, idBaseUrl, prefix, fetchFn });
+            const fetchFn = makeMockFetchFn();
+            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
+                baseUrl,
+                idBaseUrl,
+                prefix,
+                fetchFn,
+                onlyData: true,
+            });
             const params = { foo: "bar", via: ["a", "b"] };
             api.idServerRequest(Method.Post, "/test", params, IdentityPrefix.V2);
             expect(fetchFn.mock.calls[0][0].searchParams.get("foo")).not.toBe("bar");
@@ -106,18 +117,27 @@ describe("FetchHttpApi", () => {
         });
 
         it("should add Authorization header if token provided", () => {
-            const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, idBaseUrl, prefix, fetchFn });
+            const fetchFn = makeMockFetchFn();
+            const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
+                baseUrl,
+                idBaseUrl,
+                prefix,
+                fetchFn,
+                onlyData: true,
+            });
             api.idServerRequest(Method.Post, "/test", {}, IdentityPrefix.V2, "token");
             expect(fetchFn.mock.calls[0][1].headers.Authorization).toBe("Bearer token");
         });
     });
 
-    it("should return the Response object if onlyData=false", async () => {
-        const res = { ok: true };
-        const fetchFn = jest.fn().mockResolvedValue(res);
-        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn, onlyData: false });
-        await expect(api.requestOtherUrl(Method.Get, "http://url")).resolves.toBe(res);
+    it("should complain if constructed without `onlyData: true`", async () => {
+        expect(
+            () =>
+                new FetchHttpApi(new TypedEventEmitter<any, any>(), {
+                    baseUrl,
+                    prefix,
+                }),
+        ).toThrow("Constructing FetchHttpApi without `onlyData=true` is no longer supported.");
     });
 
     it("should set an Accept header, and parse the response as JSON, by default", async () => {
@@ -165,37 +185,40 @@ describe("FetchHttpApi", () => {
     });
 
     it("should send token via query params if useAuthorizationHeader=false", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
             useAuthorizationHeader: false,
+            onlyData: true,
         });
         await api.authedRequest(Method.Get, "/path");
         expect(fetchFn.mock.calls[0][0].searchParams.get("access_token")).toBe("token");
     });
 
     it("should send token via headers by default", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
+            onlyData: true,
         });
         await api.authedRequest(Method.Get, "/path");
         expect(fetchFn.mock.calls[0][1].headers["Authorization"]).toBe("Bearer token");
     });
 
     it("should not send a token if not calling `authedRequest`", () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
+            onlyData: true,
         });
         api.request(Method.Get, "/path");
         expect(fetchFn.mock.calls[0][0].searchParams.get("access_token")).toBeFalsy();
@@ -203,13 +226,14 @@ describe("FetchHttpApi", () => {
     });
 
     it("should ensure no token is leaked out via query params if sending via headers", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
             useAuthorizationHeader: true,
+            onlyData: true,
         });
         await api.authedRequest(Method.Get, "/path", { access_token: "123" });
         expect(fetchFn.mock.calls[0][0].searchParams.get("access_token")).toBeFalsy();
@@ -217,26 +241,28 @@ describe("FetchHttpApi", () => {
     });
 
     it("should not override manually specified access token via query params", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
             useAuthorizationHeader: false,
+            onlyData: true,
         });
         await api.authedRequest(Method.Get, "/path", { access_token: "RealToken" });
         expect(fetchFn.mock.calls[0][0].searchParams.get("access_token")).toBe("RealToken");
     });
 
     it("should not override manually specified access token via header", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+        const fetchFn = makeMockFetchFn();
         const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), {
             baseUrl,
             prefix,
             fetchFn,
             accessToken: "token",
             useAuthorizationHeader: true,
+            onlyData: true,
         });
         await api.authedRequest(Method.Get, "/path", undefined, undefined, {
             headers: { Authorization: "Bearer RealToken" },
@@ -245,8 +271,8 @@ describe("FetchHttpApi", () => {
     });
 
     it("should not override Accept header", async () => {
-        const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn });
+        const fetchFn = makeMockFetchFn();
+        const api = new FetchHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn, onlyData: true });
         await api.authedRequest(Method.Get, "/path", undefined, undefined, {
             headers: { Accept: "text/html" },
         });
@@ -269,7 +295,7 @@ describe("FetchHttpApi", () => {
             ),
         });
         const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
-        const api = new FetchHttpApi(emitter, { baseUrl, prefix, fetchFn });
+        const api = new FetchHttpApi(emitter, { baseUrl, prefix, fetchFn, onlyData: true });
 
         await Promise.all([
             emitPromise(emitter, HttpApiEvent.NoConsent),
@@ -279,9 +305,9 @@ describe("FetchHttpApi", () => {
 
     describe("authedRequest", () => {
         it("should not include token if unset", async () => {
-            const fetchFn = jest.fn().mockResolvedValue({ ok: true });
+            const fetchFn = makeMockFetchFn();
             const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
-            const api = new FetchHttpApi(emitter, { baseUrl, prefix, fetchFn });
+            const api = new FetchHttpApi(emitter, { baseUrl, prefix, fetchFn, onlyData: true });
             await api.authedRequest(Method.Post, "/account/password");
             expect(fetchFn.mock.calls[0][1].headers.Authorization).toBeUndefined();
         });
@@ -310,6 +336,7 @@ describe("FetchHttpApi", () => {
                 const okayResponse = {
                     ok: true,
                     status: 200,
+                    json: jest.fn().mockResolvedValue({ x: 1 }),
                 };
 
                 describe("without a tokenRefreshFunction", () => {
@@ -317,7 +344,14 @@ describe("FetchHttpApi", () => {
                         const fetchFn = jest.fn().mockResolvedValue(unknownTokenResponse);
                         const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
                         jest.spyOn(emitter, "emit");
-                        const api = new FetchHttpApi(emitter, { baseUrl, prefix, fetchFn, accessToken, refreshToken });
+                        const api = new FetchHttpApi(emitter, {
+                            baseUrl,
+                            prefix,
+                            fetchFn,
+                            accessToken,
+                            refreshToken,
+                            onlyData: true,
+                        });
                         await expect(api.authedRequest(Method.Post, "/account/password")).rejects.toThrow(
                             unknownTokenErr,
                         );
@@ -339,6 +373,7 @@ describe("FetchHttpApi", () => {
                             tokenRefreshFunction,
                             accessToken,
                             refreshToken,
+                            onlyData: true,
                         });
                         await expect(api.authedRequest(Method.Post, "/account/password")).rejects.toThrow(
                             unknownTokenErr,
@@ -360,6 +395,7 @@ describe("FetchHttpApi", () => {
                             tokenRefreshFunction,
                             accessToken,
                             refreshToken,
+                            onlyData: true,
                         });
                         await expect(api.authedRequest(Method.Post, "/account/password")).rejects.toThrow(
                             unknownTokenErr,
@@ -388,11 +424,12 @@ describe("FetchHttpApi", () => {
                             tokenRefreshFunction,
                             accessToken,
                             refreshToken,
+                            onlyData: true,
                         });
                         const result = await api.authedRequest(Method.Post, "/account/password", undefined, undefined, {
                             headers: {},
                         });
-                        expect(result).toEqual(okayResponse);
+                        expect(result).toEqual({ x: 1 });
                         expect(tokenRefreshFunction).toHaveBeenCalledWith(refreshToken);
 
                         expect(fetchFn).toHaveBeenCalledTimes(2);
@@ -431,6 +468,7 @@ describe("FetchHttpApi", () => {
                             tokenRefreshFunction,
                             accessToken,
                             refreshToken,
+                            onlyData: true,
                         });
                         await expect(api.authedRequest(Method.Post, "/account/password")).rejects.toThrow(
                             unknownTokenErr,
@@ -486,6 +524,7 @@ describe("FetchHttpApi", () => {
                             tokenRefreshFunction,
                             accessToken,
                             refreshToken,
+                            onlyData: true,
                         });
                         await expect(api.authedRequest(Method.Post, "/account/password")).rejects.toThrow(
                             unknownTokenErr,
@@ -506,7 +545,7 @@ describe("FetchHttpApi", () => {
         const makeApi = (thisBaseUrl = baseUrl): FetchHttpApi<any> => {
             const fetchFn = jest.fn();
             const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
-            return new FetchHttpApi(emitter, { baseUrl: thisBaseUrl, prefix, fetchFn });
+            return new FetchHttpApi(emitter, { baseUrl: thisBaseUrl, prefix, fetchFn, onlyData: true });
         };
 
         type TestParams = {
@@ -559,7 +598,13 @@ describe("FetchHttpApi", () => {
             const makeApiWithExtraParams = (extraParams: QueryDict): FetchHttpApi<any> => {
                 const fetchFn = jest.fn();
                 const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
-                return new FetchHttpApi(emitter, { baseUrl: localBaseUrl, prefix, fetchFn, extraParams });
+                return new FetchHttpApi(emitter, {
+                    baseUrl: localBaseUrl,
+                    prefix,
+                    fetchFn,
+                    onlyData: true,
+                    extraParams,
+                });
             };
 
             const userId = "@rsb-tbg:localhost";
@@ -612,7 +657,7 @@ describe("FetchHttpApi", () => {
             it("should work when extraParams is undefined", () => {
                 const fetchFn = jest.fn();
                 const emitter = new TypedEventEmitter<HttpApiEvent, HttpApiEventHandlerMap>();
-                const api = new FetchHttpApi(emitter, { baseUrl: localBaseUrl, prefix, fetchFn });
+                const api = new FetchHttpApi(emitter, { baseUrl: localBaseUrl, prefix, fetchFn, onlyData: true });
 
                 const queryParams = { userId: "123" };
                 const result = api.getUrl("/test", queryParams);
@@ -645,10 +690,11 @@ describe("FetchHttpApi", () => {
             prefix,
             fetchFn,
             logger: mockLogger,
+            onlyData: true,
         });
         const prom = api.requestOtherUrl(Method.Get, "https://server:8448/some/path?query=param#fragment");
         jest.advanceTimersByTime(1234);
-        responseResolvers.resolve({ ok: true, status: 200, text: () => Promise.resolve("RESPONSE") } as Response);
+        responseResolvers.resolve({ ok: true, status: 200, json: () => Promise.resolve("RESPONSE") } as Response);
         await prom;
         expect(mockLogger.debug).not.toHaveBeenCalledWith("fragment");
         expect(mockLogger.debug).not.toHaveBeenCalledWith("query");
@@ -691,6 +737,7 @@ describe("FetchHttpApi", () => {
             tokenRefreshFunction,
             accessToken: "ACCESS_TOKEN",
             refreshToken: "REFRESH_TOKEN",
+            onlyData: true,
         });
 
         const prom1 = api.authedRequest(Method.Get, "/path1");
@@ -746,6 +793,7 @@ describe("FetchHttpApi", () => {
             tokenRefreshFunction,
             accessToken: "ACCESS_TOKEN",
             refreshToken: "REFRESH_TOKEN",
+            onlyData: true,
         });
 
         const prom1 = api.authedRequest(Method.Get, "/path1");
@@ -783,3 +831,7 @@ describe("FetchHttpApi", () => {
         expect(api.opts.refreshToken).toBe("NEW_REFRESH_TOKEN");
     });
 });
+
+function makeMockFetchFn(): MockedFunction<any> {
+    return jest.fn().mockResolvedValue({ ok: true, json: jest.fn().mockResolvedValue({}) });
+}
diff --git a/spec/unit/http-api/index.spec.ts b/spec/unit/http-api/index.spec.ts
index 9eb321891..2019a78eb 100644
--- a/spec/unit/http-api/index.spec.ts
+++ b/spec/unit/http-api/index.spec.ts
@@ -62,7 +62,7 @@ describe("MatrixHttpApi", () => {
     it("should fall back to `fetch` where xhr is unavailable", async () => {
         globalThis.XMLHttpRequest = undefined!;
         const fetchFn = jest.fn().mockResolvedValue({ ok: true, json: jest.fn().mockResolvedValue({}) });
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn, onlyData: true });
         upload = api.uploadContent({} as File);
         await upload;
         expect(fetchFn).toHaveBeenCalled();
@@ -70,7 +70,7 @@ describe("MatrixHttpApi", () => {
 
     it("should prefer xhr where available", () => {
         const fetchFn = jest.fn().mockResolvedValue({ ok: true });
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, fetchFn, onlyData: true });
         upload = api.uploadContent({} as File);
         expect(fetchFn).not.toHaveBeenCalled();
         expect(xhr.open).toHaveBeenCalled();
@@ -82,6 +82,7 @@ describe("MatrixHttpApi", () => {
             prefix,
             accessToken: "token",
             useAuthorizationHeader: false,
+            onlyData: true,
         });
         upload = api.uploadContent({} as File);
         expect(xhr.open).toHaveBeenCalledWith(
@@ -96,6 +97,7 @@ describe("MatrixHttpApi", () => {
             baseUrl,
             prefix,
             accessToken: "token",
+            onlyData: true,
         });
         upload = api.uploadContent({} as File);
         expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/v3/upload");
@@ -103,7 +105,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should include filename by default", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File, { name: "name" });
         expect(xhr.open).toHaveBeenCalledWith(
             Method.Post,
@@ -112,13 +114,13 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should allow not sending the filename", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File, { name: "name", includeFilename: false });
         expect(xhr.open).toHaveBeenCalledWith(Method.Post, baseUrl.toLowerCase() + "/_matrix/media/v3/upload");
     });
 
     it("should abort xhr when the upload is aborted", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
         api.cancelUpload(upload);
         expect(xhr.abort).toHaveBeenCalled();
@@ -126,7 +128,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should timeout if no progress in 30s", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
         jest.advanceTimersByTime(25000);
         // @ts-ignore
@@ -138,7 +140,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should call progressHandler", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         const progressHandler = jest.fn();
         upload = api.uploadContent({} as File, { progressHandler });
         const progressEvent = new Event("progress") as ProgressEvent;
@@ -154,7 +156,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should error when no response body", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
 
         xhr.readyState = DONE;
@@ -167,7 +169,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should error on a 400-code", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
 
         xhr.readyState = DONE;
@@ -184,7 +186,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should return response on successful upload", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
 
         xhr.readyState = DONE;
@@ -198,14 +200,14 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should abort xhr when calling `cancelUpload`", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
         expect(api.cancelUpload(upload)).toBeTruthy();
         expect(xhr.abort).toHaveBeenCalled();
     });
 
     it("should return false when `cancelUpload` is called but unsuccessful", async () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
 
         xhr.readyState = DONE;
@@ -220,7 +222,7 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should return active uploads in `getCurrentUploads`", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, onlyData: true });
         upload = api.uploadContent({} as File);
         expect(api.getCurrentUploads().find((u) => u.promise === upload)).toBeTruthy();
         api.cancelUpload(upload);
@@ -228,7 +230,12 @@ describe("MatrixHttpApi", () => {
     });
 
     it("should return expected object from `getContentUri`", () => {
-        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), { baseUrl, prefix, accessToken: "token" });
+        const api = new MatrixHttpApi(new TypedEventEmitter<any, any>(), {
+            baseUrl,
+            prefix,
+            accessToken: "token",
+            onlyData: true,
+        });
         expect(api.getContentUri()).toMatchSnapshot();
     });
 });
diff --git a/src/client.ts b/src/client.ts
index d2de367e2..8ffb37f61 100644
--- a/src/client.ts
+++ b/src/client.ts
@@ -6843,9 +6843,7 @@ export class MatrixClient extends TypedEventEmitter<EmittedEvents, ClientEventHa
      *
      * @param opts -  options object
      *
-     * @returns Promise which resolves to response object, as
-     *    determined by this.opts.onlyData, opts.rawResponse, and
-     *    opts.onlyContentUri.  Rejects with an error (usually a MatrixError).
+     * @returns Promise which resolves to response object, or rejects with an error (usually a MatrixError).
      */
     public uploadContent(file: FileType, opts?: UploadOpts): Promise<UploadResponse> {
         return this.http.uploadContent(file, opts);
diff --git a/src/http-api/fetch.ts b/src/http-api/fetch.ts
index 026f4b042..d6d1b5a52 100644
--- a/src/http-api/fetch.ts
+++ b/src/http-api/fetch.ts
@@ -34,22 +34,6 @@ import { anySignal, parseErrorResponse, timeoutSignal } from "./utils.ts";
 import { type QueryDict } from "../utils.ts";
 import { TokenRefresher, TokenRefreshOutcome } from "./refresh.ts";
 
-interface TypedResponse<T> extends Response {
-    json(): Promise<T>;
-}
-
-/**
- * The type returned by {@link FetchHttpApi.request}, etc.
- *
- * If {@link IHttpOpts.onlyData} is unset or false, then the request methods return a
- * {@link https://developer.mozilla.org/en-US/docs/Web/API/Response Response} object,
- * which we abstract via `TypedResponse`. Otherwise, we just cast it to `T`.
- *
- * @typeParam T - The type (specified by the application on the request method) that we will cast the response to.
- * @typeParam O - The type of the options object on the {@link FetchHttpApi} instance.
- */
-export type ResponseType<T, O extends IHttpOpts> = O extends { onlyData: true } | undefined ? T : TypedResponse<T>;
-
 export class FetchHttpApi<O extends IHttpOpts> {
     private abortController = new AbortController();
     private readonly tokenRefresher: TokenRefresher;
@@ -59,7 +43,9 @@ export class FetchHttpApi<O extends IHttpOpts> {
         public readonly opts: O,
     ) {
         checkObjectHasKeys(opts, ["baseUrl", "prefix"]);
-        opts.onlyData = !!opts.onlyData;
+        if (!opts.onlyData) {
+            throw new Error("Constructing FetchHttpApi without `onlyData=true` is no longer supported.");
+        }
         opts.useAuthorizationHeader = opts.useAuthorizationHeader ?? true;
 
         this.tokenRefresher = new TokenRefresher(opts);
@@ -91,7 +77,7 @@ export class FetchHttpApi<O extends IHttpOpts> {
         params: Record<string, string | string[]> | undefined,
         prefix: string,
         accessToken?: string,
-    ): Promise<ResponseType<T, O>> {
+    ): Promise<T> {
         if (!this.opts.idBaseUrl) {
             throw new Error("No identity server base URL set");
         }
@@ -132,17 +118,8 @@ export class FetchHttpApi<O extends IHttpOpts> {
      * When `paramOpts.doNotAttemptTokenRefresh` is true, token refresh will not be attempted
      * when an expired token is encountered. Used to only attempt token refresh once.
      *
-     * @returns Promise which resolves to
-     * ```
-     * {
-     *     data: {Object},
-     *     headers: {Object},
-     *     code: {Number},
-     * }
-     * ```
-     * If `onlyData` is set, this will resolve to the `data` object only.
-     * @returns Rejects with an error if a problem occurred.
-     * This includes network problems and Matrix-specific error JSON.
+     * @returns The parsed response.
+     * @throws Error if a problem occurred. This includes network problems and Matrix-specific error JSON.
      */
     public authedRequest<T>(
         method: Method,
@@ -150,7 +127,7 @@ export class FetchHttpApi<O extends IHttpOpts> {
         queryParams: QueryDict = {},
         body?: Body,
         paramOpts: IRequestOpts = {},
-    ): Promise<ResponseType<T, O>> {
+    ): Promise<T> {
         return this.doAuthedRequest<T>(1, method, path, queryParams, body, paramOpts);
     }
 
@@ -162,7 +139,7 @@ export class FetchHttpApi<O extends IHttpOpts> {
         queryParams: QueryDict,
         body?: Body,
         paramOpts: IRequestOpts = {},
-    ): Promise<ResponseType<T, O>> {
+    ): Promise<T> {
         // avoid mutating paramOpts so they can be used on retry
         const opts = deepCopy(paramOpts);
         // we have to manually copy the abortSignal over as it is not a plain object
@@ -228,18 +205,8 @@ export class FetchHttpApi<O extends IHttpOpts> {
      *
      * @param opts - additional options
      *
-     * @returns Promise which resolves to
-     * ```
-     * {
-     *  data: {Object},
-     *  headers: {Object},
-     *  code: {Number},
-     * }
-     * ```
-     * If `onlyData</code> is set, this will resolve to the <code>data`
-     * object only.
-     * @returns Rejects with an error if a problem
-     * occurred. This includes network problems and Matrix-specific error JSON.
+     * @returns The parsed response.
+     * @throws Error if a problem occurred. This includes network problems and Matrix-specific error JSON.
      */
     public request<T>(
         method: Method,
@@ -247,7 +214,7 @@ export class FetchHttpApi<O extends IHttpOpts> {
         queryParams?: QueryDict,
         body?: Body,
         opts?: IRequestOpts,
-    ): Promise<ResponseType<T, O>> {
+    ): Promise<T> {
         const fullUri = this.getUrl(path, queryParams, opts?.prefix, opts?.baseUrl);
         return this.requestOtherUrl<T>(method, fullUri, body, opts);
     }
@@ -261,17 +228,15 @@ export class FetchHttpApi<O extends IHttpOpts> {
      *
      * @param opts - additional options
      *
-     * @returns Promise which resolves to data unless `onlyData` is specified as false,
-     * where the resolved value will be a fetch Response object.
-     * @returns Rejects with an error if a problem
-     * occurred. This includes network problems and Matrix-specific error JSON.
+     * @returns The parsed response.
+     * @throws Error if a problem occurred. This includes network problems and Matrix-specific error JSON.
      */
     public async requestOtherUrl<T>(
         method: Method,
         url: URL | string,
         body?: Body,
         opts: BaseRequestOpts = {},
-    ): Promise<ResponseType<T, O>> {
+    ): Promise<T> {
         if (opts.json !== undefined && opts.rawResponseBody !== undefined) {
             throw new Error("Invalid call to `FetchHttpApi` sets both `opts.json` and `opts.rawResponseBody`");
         }
@@ -349,14 +314,12 @@ export class FetchHttpApi<O extends IHttpOpts> {
             throw parseErrorResponse(res, await res.text());
         }
 
-        if (!this.opts.onlyData) {
-            return res as ResponseType<T, O>;
-        } else if (opts.rawResponseBody) {
-            return (await res.blob()) as ResponseType<T, O>;
+        if (opts.rawResponseBody) {
+            return (await res.blob()) as T;
         } else if (jsonResponse) {
             return await res.json();
         } else {
-            return (await res.text()) as ResponseType<T, O>;
+            return (await res.text()) as T;
         }
     }
 
diff --git a/src/http-api/index.ts b/src/http-api/index.ts
index 1474cdde9..346a9e549 100644
--- a/src/http-api/index.ts
+++ b/src/http-api/index.ts
@@ -48,9 +48,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
      *
      * @param opts - options object
      *
-     * @returns Promise which resolves to response object, as
-     *    determined by this.opts.onlyData, opts.rawResponse, and
-     *    opts.onlyContentUri.  Rejects with an error (usually a MatrixError).
+     * @returns Promise which resolves to response object, or rejects with an error (usually a MatrixError).
      */
     public uploadContent(file: FileType, opts: UploadOpts = {}): Promise<UploadResponse> {
         const includeFilename = opts.includeFilename ?? true;
@@ -149,11 +147,7 @@ export class MatrixHttpApi<O extends IHttpOpts> extends FetchHttpApi<O> {
                 prefix: MediaPrefix.V3,
                 headers,
                 abortSignal: abortController.signal,
-            })
-                .then((response) => {
-                    return this.opts.onlyData ? <UploadResponse>response : response.json();
-                })
-                .then(uploadResolvers.resolve, uploadResolvers.reject);
+            }).then(uploadResolvers.resolve, uploadResolvers.reject);
         }
 
         // remove the upload from the list on completion
diff --git a/src/http-api/interface.ts b/src/http-api/interface.ts
index 5d56dd7a7..40100a5b5 100644
--- a/src/http-api/interface.ts
+++ b/src/http-api/interface.ts
@@ -69,10 +69,7 @@ export interface IHttpOpts {
     tokenRefreshFunction?: TokenRefreshFunction;
     useAuthorizationHeader?: boolean; // defaults to true
 
-    /**
-     * Normally, methods in `FetchHttpApi` will return a {@link https://developer.mozilla.org/en-US/docs/Web/API/Response Response} object.
-     * If this is set to `true`, they instead return the response body.
-     */
+    /** For historical reasons, must be set to `true`. Will eventually be removed. */
     onlyData?: boolean;
 
     localTimeoutMs?: number;
@@ -103,11 +100,10 @@ export interface BaseRequestOpts extends Pick<RequestInit, "priority"> {
      *
      *  * Set `Accept: application/json` in the request headers (again, unless overridden by {@link headers}).
      *
-     *  * If `IHTTPOpts.onlyData` is set to `true` on the `FetchHttpApi` instance, parse the response as
-     *    JSON and return the parsed response.
+     *  * Parse the response as JSON and return the parsed response.
      *
-     * Setting this to `false` inhibits all three behaviors, and (if `IHTTPOpts.onlyData` is set to `true`) the response
-     * is instead parsed as a UTF-8 string. It defaults to `true`, unless {@link rawResponseBody} is set.
+     * Setting this to `false` inhibits all three behaviors, and the response is instead parsed as a UTF-8 string. It
+     * defaults to `true`, unless {@link rawResponseBody} is set.
      *
      * @deprecated Instead of setting this to `false`, set {@link rawResponseBody} to `true`.
      */
@@ -118,9 +114,8 @@ export interface BaseRequestOpts extends Pick<RequestInit, "priority"> {
      *
      *  * Inhibits the automatic addition of `Accept: application/json` in the request headers.
      *
-     *  * Assuming `IHTTPOpts.onlyData` is set to `true` on the `FetchHttpApi` instance, causes the
-     *    raw response to be returned as a {@link https://developer.mozilla.org/en-US/docs/Web/API/Blob|Blob}
-     *    instead of parsing it as `json`.
+     *  * Causes the raw response to be returned as a {@link https://developer.mozilla.org/en-US/docs/Web/API/Blob|Blob}
+     *    instead of parsing it as JSON.
      */
     rawResponseBody?: boolean;
 }