diff --git a/services/common/kinto-http-client.js b/services/common/kinto-http-client.js
index deda29e80d24..d03559237073 100644
--- a/services/common/kinto-http-client.js
+++ b/services/common/kinto-http-client.js
@@ -2500,7 +2500,7 @@ XPCOMUtils.defineLazyGlobalGetters(global, ["fetch"]);
             {
                 headers: options.headers ? options.headers : {},
                 path: path + "?" + querystring,
-            }, 
+            },
             // N.B. This doesn't use _getRetry, because all calls to
             // `paginatedList` are assumed to come from calls that already
             // used `_getRetry` at e.g. the bucket or collection level.
diff --git a/services/settings/RemoteSettingsClient.jsm b/services/settings/RemoteSettingsClient.jsm
index 74ba0d9efa3c..138ef470a84c 100644
--- a/services/settings/RemoteSettingsClient.jsm
+++ b/services/settings/RemoteSettingsClient.jsm
@@ -765,24 +765,17 @@ class RemoteSettingsClient extends EventEmitter {
     options = {}
   ) {
     const { retry = false } = options;
+    const since = retry || !localTimestamp ? undefined : `${localTimestamp}`;
 
-    // Fetch collection metadata and list of changes from server
-    // (or all records on retry).
-    const client = this.httpClient();
-    const [
+    // Fetch collection metadata and list of changes from server.
+    console.debug(
+      `Fetch changes from server (expected=${expectedTimestamp}, since=${since})`
+    );
+    const {
       metadata,
-      { data: remoteRecords, last_modified: remoteTimestamp },
-    ] = await Promise.all([
-      client.getData({
-        query: { _expected: expectedTimestamp },
-      }),
-      client.listRecords({
-        filters: {
-          _expected: expectedTimestamp,
-        },
-        since: retry || !localTimestamp ? undefined : `${localTimestamp}`,
-      }),
-    ]);
+      remoteTimestamp,
+      remoteRecords,
+    } = await this._fetchChangeset(expectedTimestamp, since);
 
     // We build a sync result, based on remote changes.
     const syncResult = {
@@ -893,6 +886,36 @@ class RemoteSettingsClient extends EventEmitter {
     return syncResult;
   }
 
+  /**
+   * Fetch information from changeset endpoint.
+   *
+   * @param expectedTimestamp cache busting value
+   * @param since timestamp of last sync (optional)
+   */
+  async _fetchChangeset(expectedTimestamp, since) {
+    const client = this.httpClient();
+    const {
+      metadata,
+      timestamp: remoteTimestamp,
+      changes: remoteRecords,
+    } = await client.execute(
+      {
+        path: `/buckets/${this.bucketName}/collections/${this.collectionName}/changeset`,
+      },
+      {
+        query: {
+          _expected: expectedTimestamp,
+          _since: since,
+        },
+      }
+    );
+    return {
+      remoteTimestamp,
+      metadata,
+      remoteRecords,
+    };
+  }
+
   /**
    * Use the filter func to filter the lists of changes obtained from synchronization,
    * and return them along with the filtered list of local records.
diff --git a/services/settings/test/unit/test_remote_settings.js b/services/settings/test/unit/test_remote_settings.js
index 2dec180e6170..0c6c94af16d9 100644
--- a/services/settings/test/unit/test_remote_settings.js
+++ b/services/settings/test/unit/test_remote_settings.js
@@ -69,11 +69,7 @@ function run_test() {
     handleResponse
   );
   server.registerPathHandler(
-    "/v1/buckets/main/collections/password-fields",
-    handleResponse
-  );
-  server.registerPathHandler(
-    "/v1/buckets/main/collections/password-fields/records",
+    "/v1/buckets/main/collections/password-fields/changeset",
     handleResponse
   );
   server.registerPathHandler(
@@ -81,15 +77,11 @@ function run_test() {
     handleResponse
   );
   server.registerPathHandler(
-    "/v1/buckets/main/collections/language-dictionaries/records",
+    "/v1/buckets/main/collections/language-dictionaries/changeset",
     handleResponse
   );
   server.registerPathHandler(
-    "/v1/buckets/main/collections/with-local-fields",
-    handleResponse
-  );
-  server.registerPathHandler(
-    "/v1/buckets/main/collections/with-local-fields/records",
+    "/v1/buckets/main/collections/with-local-fields/changeset",
     handleResponse
   );
   server.registerPathHandler("/fake-x5u", handleResponse);
@@ -910,26 +902,6 @@ function getSampleResponse(req, port) {
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields": {
-      sampleHeaders: [
-        "Access-Control-Allow-Origin: *",
-        "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
-        "Content-Type: application/json; charset=UTF-8",
-        "Server: waitress",
-        'Etag: "1234"',
-      ],
-      status: { status: 200, statusText: "OK" },
-      responseBody: JSON.stringify({
-        data: {
-          id: "password-fields",
-          last_modified: 1234,
-          signature: {
-            signature: "abcdef",
-            x5u: `http://localhost:${port}/fake-x5u`,
-          },
-        },
-      }),
-    },
     "GET:/fake-x5u": {
       sampleHeaders: ["Content-Type: application/octet-stream"],
       status: { status: 200, statusText: "OK" },
@@ -940,7 +912,7 @@ ZARKjbu1TuYQHf0fs+GwID8zeLc2zJL7UzcHFwwQ6Nda9OJN4uPAuC/BKaIpxCLL
 wNuvFqc=
 -----END CERTIFICATE-----`,
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=2000&_sort=-last_modified": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=2000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -950,7 +922,16 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        timestamp: 3000,
+        metadata: {
+          id: "password-fields",
+          last_modified: 1234,
+          signature: {
+            signature: "abcdef",
+            x5u: `http://localhost:${port}/fake-x5u`,
+          },
+        },
+        changes: [
           {
             id: "9d500963-d80e-3a91-6e74-66f3811b99cc",
             last_modified: 3000,
@@ -960,7 +941,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=3001&_sort=-last_modified&_since=3000": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=3001&_since=3000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -970,7 +951,9 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        metadata: {},
+        timestamp: 4000,
+        changes: [
           {
             id: "aabad965-e556-ffe7-4191-074f5dee3df3",
             last_modified: 4000,
@@ -986,7 +969,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=4001&_sort=-last_modified&_since=4000": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=4001&_since=4000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -996,7 +979,9 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        metadata: {},
+        timestamp: 5000,
+        changes: [
           {
             id: "aabad965-e556-ffe7-4191-074f5dee3df3",
             deleted: true,
@@ -1004,7 +989,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=10000&_sort=-last_modified&_since=9999": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=10000&_since=9999": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1018,7 +1003,7 @@ wNuvFqc=
         error: "Service Unavailable",
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=10001&_sort=-last_modified&_since=10000": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=10001&_since=10000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1029,7 +1014,7 @@ wNuvFqc=
       status: { status: 200, statusText: "OK" },
       responseBody: "<invalid json",
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=11001&_sort=-last_modified&_since=11000": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=11001&_since=11000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1038,7 +1023,7 @@ wNuvFqc=
       ],
       status: { status: 503, statusText: "Service Unavailable" },
       responseBody: {
-        data: [
+        changes: [
           {
             id: "c4f021e3-f68c-4269-ad2a-d4ba87762b35",
             last_modified: 4000,
@@ -1083,7 +1068,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/password-fields/records?_expected=1337&_sort=-last_modified": {
+    "GET:/v1/buckets/main/collections/password-fields/changeset?_expected=1337": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1093,7 +1078,9 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        metadata: {},
+        timestamp: 3000,
+        changes: [
           {
             id: "312cc78d-9c1f-4291-a4fa-a1be56f6cc69",
             last_modified: 3000,
@@ -1123,7 +1110,7 @@ wNuvFqc=
         },
       }),
     },
-    "GET:/v1/buckets/main/collections/language-dictionaries/records": {
+    "GET:/v1/buckets/main/collections/language-dictionaries/changeset": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1133,7 +1120,16 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        timestamp: 5000000000000,
+        metadata: {
+          id: "language-dictionaries",
+          last_modified: 1234,
+          signature: {
+            signature: "xyz",
+            x5u: `http://localhost:${port}/fake-x5u`,
+          },
+        },
+        changes: [
           {
             id: "xx",
             last_modified: 5000000000000,
@@ -1152,27 +1148,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/with-local-fields": {
-      sampleHeaders: [
-        "Access-Control-Allow-Origin: *",
-        "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
-        "Content-Type: application/json; charset=UTF-8",
-        "Server: waitress",
-        'Etag: "1234"',
-      ],
-      status: { status: 200, statusText: "OK" },
-      responseBody: JSON.stringify({
-        data: {
-          id: "with-local-fields",
-          last_modified: 1234,
-          signature: {
-            signature: "xyz",
-            x5u: `http://localhost:${port}/fake-x5u`,
-          },
-        },
-      }),
-    },
-    "GET:/v1/buckets/main/collections/with-local-fields/records?_expected=2000&_sort=-last_modified": {
+    "GET:/v1/buckets/main/collections/with-local-fields/changeset?_expected=2000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1182,7 +1158,16 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        timestamp: 2000,
+        metadata: {
+          id: "with-local-fields",
+          last_modified: 1234,
+          signature: {
+            signature: "xyz",
+            x5u: `http://localhost:${port}/fake-x5u`,
+          },
+        },
+        changes: [
           {
             id: "c74279ce-fb0a-42a6-ae11-386b567a6119",
             last_modified: 2000,
@@ -1190,7 +1175,7 @@ wNuvFqc=
         ],
       },
     },
-    "GET:/v1/buckets/main/collections/with-local-fields/records?_expected=3000&_sort=-last_modified&_since=2000": {
+    "GET:/v1/buckets/main/collections/with-local-fields/changeset?_expected=3000&_since=2000": {
       sampleHeaders: [
         "Access-Control-Allow-Origin: *",
         "Access-Control-Expose-Headers: Retry-After, Content-Length, Alert, Backoff",
@@ -1200,7 +1185,9 @@ wNuvFqc=
       ],
       status: { status: 200, statusText: "OK" },
       responseBody: {
-        data: [
+        timestamp: 3000,
+        metadata: {},
+        changes: [
           {
             id: "1f5c98b9-6d93-4c13-aa26-978b38695096",
             last_modified: 3000,
diff --git a/services/settings/test/unit/test_remote_settings_signatures.js b/services/settings/test/unit/test_remote_settings_signatures.js
index 0f51b27e43b1..b2af73fa4704 100644
--- a/services/settings/test/unit/test_remote_settings_signatures.js
+++ b/services/settings/test/unit/test_remote_settings_signatures.js
@@ -114,40 +114,11 @@ add_task(async function test_check_signatures() {
 add_task(async function test_check_synchronization_with_signatures() {
   const port = server.identity.primaryPort;
 
+  const x5u = `http://localhost:${port}/test_remote_settings_signatures/test_cert_chain.pem`;
+
   // Telemetry reports.
   const TELEMETRY_HISTOGRAM_KEY = client.identifier;
 
-  // a response to give the client when the cert chain is expected
-  function makeMetaResponseBody(lastModified, signature) {
-    return {
-      data: {
-        id: "signed",
-        last_modified: lastModified,
-        signature: {
-          x5u: `http://localhost:${port}/test_remote_settings_signatures/test_cert_chain.pem`,
-          public_key: "fake",
-          "content-signature": `x5u=http://localhost:${port}/test_remote_settings_signatures/test_cert_chain.pem;p384ecdsa=${signature}`,
-          signature_encoding: "rs_base64url",
-          signature,
-          hash_algorithm: "sha384",
-          ref: "1yryrnmzou5rf31ou80znpnq8n",
-        },
-      },
-    };
-  }
-
-  function makeMetaResponse(eTag, body, comment) {
-    return {
-      comment,
-      sampleHeaders: [
-        "Content-Type: application/json; charset=UTF-8",
-        `ETag: \"${eTag}\"`,
-      ],
-      status: { status: 200, statusText: "OK" },
-      responseBody: JSON.stringify(body),
-    };
-  }
-
   function registerHandlers(responses) {
     function handleResponse(serverTimeMillis, request, response) {
       const key = `${request.method}:${request.path}?${request.queryString}`;
@@ -292,35 +263,28 @@ add_task(async function test_check_synchronization_with_signatures() {
       'ETag: "1000"',
     ],
     status: { status: 200, statusText: "OK" },
-    responseBody: JSON.stringify({ data: [] }),
+    responseBody: JSON.stringify({
+      timestamp: 1000,
+      metadata: {
+        signature: {
+          x5u,
+          signature:
+            "vxuAg5rDCB-1pul4a91vqSBQRXJG_j7WOYUTswxRSMltdYmbhLRH8R8brQ9YKuNDF56F-w6pn4HWxb076qgKPwgcEBtUeZAO_RtaHXRkRUUgVzAr86yQL4-aJTbv3D6u",
+        },
+      },
+      changes: [],
+    }),
   };
 
-  // Valid signature for empty collection.
-  const RESPONSE_BODY_META_EMPTY_SIG = makeMetaResponseBody(
-    1000,
-    "vxuAg5rDCB-1pul4a91vqSBQRXJG_j7WOYUTswxRSMltdYmbhLRH8R8brQ9YKuNDF56F-w6pn4HWxb076qgKPwgcEBtUeZAO_RtaHXRkRUUgVzAr86yQL4-aJTbv3D6u"
-  );
-
-  // The collection metadata containing the signature for the empty
-  // collection.
-  const RESPONSE_META_EMPTY_SIG = makeMetaResponse(
-    1000,
-    RESPONSE_BODY_META_EMPTY_SIG,
-    "RESPONSE_META_EMPTY_SIG"
-  );
-
   // Here, we map request method and path to the available responses
   const emptyCollectionResponses = {
     "GET:/test_remote_settings_signatures/test_cert_chain.pem?": [
       RESPONSE_CERT_CHAIN,
     ],
     "GET:/v1/?": [RESPONSE_SERVER_SETTINGS],
-    "GET:/v1/buckets/main/collections/signed/records?_expected=1000&_sort=-last_modified": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=1000": [
       RESPONSE_EMPTY_INITIAL,
     ],
-    "GET:/v1/buckets/main/collections/signed?_expected=1000": [
-      RESPONSE_META_EMPTY_SIG,
-    ],
   };
 
   //
@@ -362,28 +326,23 @@ add_task(async function test_check_synchronization_with_signatures() {
       'ETag: "3000"',
     ],
     status: { status: 200, statusText: "OK" },
-    responseBody: JSON.stringify({ data: [RECORD2, RECORD1] }),
+    responseBody: JSON.stringify({
+      timestamp: 3000,
+      metadata: {
+        signature: {
+          x5u,
+          signature:
+            "dwhJeypadNIyzGj3QdI0KMRTPnHhFPF_j73mNrsPAHKMW46S2Ftf4BzsPMvPMB8h0TjDus13wo_R4l432DHe7tYyMIWXY0PBeMcoe5BREhFIxMxTsh9eGVXBD1e3UwRy",
+        },
+      },
+      changes: [RECORD2, RECORD1],
+    }),
   };
 
-  const RESPONSE_BODY_META_TWO_ITEMS_SIG = makeMetaResponseBody(
-    3000,
-    "dwhJeypadNIyzGj3QdI0KMRTPnHhFPF_j73mNrsPAHKMW46S2Ftf4BzsPMvPMB8h0TjDus13wo_R4l432DHe7tYyMIWXY0PBeMcoe5BREhFIxMxTsh9eGVXBD1e3UwRy"
-  );
-
-  // A signature response for the collection containg RECORD1 and RECORD2
-  const RESPONSE_META_TWO_ITEMS_SIG = makeMetaResponse(
-    3000,
-    RESPONSE_BODY_META_TWO_ITEMS_SIG,
-    "RESPONSE_META_TWO_ITEMS_SIG"
-  );
-
   const twoItemsResponses = {
-    "GET:/v1/buckets/main/collections/signed/records?_expected=3000&_sort=-last_modified&_since=1000": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=3000&_since=1000": [
       RESPONSE_TWO_ADDED,
     ],
-    "GET:/v1/buckets/main/collections/signed?_expected=3000": [
-      RESPONSE_META_TWO_ITEMS_SIG,
-    ],
   };
   registerHandlers(twoItemsResponses);
   await client.maybeSync(3000);
@@ -397,6 +356,8 @@ add_task(async function test_check_synchronization_with_signatures() {
   //
   // Check the collection with one addition and one removal has a valid
   // signature
+  const THREE_ITEMS_SIG =
+    "MIEmNghKnkz12UodAAIc3q_Y4a3IJJ7GhHF4JYNYmm8avAGyPM9fYU7NzVo94pzjotG7vmtiYuHyIX2rTHTbT587w0LdRWxipgFd_PC1mHiwUyjFYNqBBG-kifYk7kEw";
 
   // Remove RECORD1, add RECORD3
   const RESPONSE_ONE_ADDED_ONE_REMOVED = {
@@ -406,28 +367,22 @@ add_task(async function test_check_synchronization_with_signatures() {
       'ETag: "4000"',
     ],
     status: { status: 200, statusText: "OK" },
-    responseBody: JSON.stringify({ data: [RECORD3, RECORD1_DELETION] }),
+    responseBody: JSON.stringify({
+      timestamp: 4000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: THREE_ITEMS_SIG,
+        },
+      },
+      changes: [RECORD3, RECORD1_DELETION],
+    }),
   };
 
-  const RESPONSE_BODY_META_THREE_ITEMS_SIG = makeMetaResponseBody(
-    4000,
-    "MIEmNghKnkz12UodAAIc3q_Y4a3IJJ7GhHF4JYNYmm8avAGyPM9fYU7NzVo94pzjotG7vmtiYuHyIX2rTHTbT587w0LdRWxipgFd_PC1mHiwUyjFYNqBBG-kifYk7kEw"
-  );
-
-  // signature response for the collection containing RECORD2 and RECORD3
-  const RESPONSE_META_THREE_ITEMS_SIG = makeMetaResponse(
-    4000,
-    RESPONSE_BODY_META_THREE_ITEMS_SIG,
-    "RESPONSE_META_THREE_ITEMS_SIG"
-  );
-
   const oneAddedOneRemovedResponses = {
-    "GET:/v1/buckets/main/collections/signed/records?_expected=4000&_sort=-last_modified&_since=3000": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=4000&_since=3000": [
       RESPONSE_ONE_ADDED_ONE_REMOVED,
     ],
-    "GET:/v1/buckets/main/collections/signed?_expected=4000": [
-      RESPONSE_META_THREE_ITEMS_SIG,
-    ],
   };
   registerHandlers(oneAddedOneRemovedResponses);
   await client.maybeSync(4000);
@@ -449,22 +404,29 @@ add_task(async function test_check_synchronization_with_signatures() {
       'ETag: "4000"',
     ],
     status: { status: 200, statusText: "OK" },
-    responseBody: JSON.stringify({ data: [] }),
+    responseBody: JSON.stringify({
+      timestamp: 4000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: THREE_ITEMS_SIG,
+        },
+      },
+      changes: [],
+    }),
   };
 
   const noOpResponses = {
-    "GET:/v1/buckets/main/collections/signed/records?_expected=4100&_sort=-last_modified&_since=4000": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=4100&_since=4000": [
       RESPONSE_EMPTY_NO_UPDATE,
     ],
-    "GET:/v1/buckets/main/collections/signed?_expected=4100": [
-      RESPONSE_META_THREE_ITEMS_SIG,
-    ],
   };
   registerHandlers(noOpResponses);
   await client.maybeSync(4100);
 
   equal((await client.get()).length, 2);
 
+  console.info("---------------------------------------------------------");
   //
   // 5.
   // - collection: [RECORD2, RECORD3] -> [RECORD2, RECORD3]
@@ -484,38 +446,42 @@ add_task(async function test_check_synchronization_with_signatures() {
       'ETag: "4000"',
     ],
     status: { status: 200, statusText: "OK" },
-    responseBody: JSON.stringify({ data: [RECORD2, RECORD3] }),
+    responseBody: JSON.stringify({
+      timestamp: 4000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: THREE_ITEMS_SIG,
+        },
+      },
+      changes: [RECORD2, RECORD3],
+    }),
   };
 
-  // Prepare a (deliberately) bad signature to check the collection state is
-  // reset if something is inconsistent
-  const RESPONSE_BODY_META_BAD_SIG = makeMetaResponseBody(
-    4000,
-    "aW52YWxpZCBzaWduYXR1cmUK"
-  );
-  const RESPONSE_META_BAD_SIG = makeMetaResponse(
-    4000,
-    RESPONSE_BODY_META_BAD_SIG,
-    "RESPONSE_META_BAD_SIG"
-  );
+  const RESPONSE_EMPTY_NO_UPDATE_BAD_SIG = {
+    ...RESPONSE_EMPTY_NO_UPDATE,
+    responseBody: JSON.stringify({
+      timestamp: 4000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: "aW52YWxpZCBzaWduYXR1cmUK",
+        },
+      },
+      changes: [],
+    }),
+  };
 
   const badSigGoodSigResponses = {
-    // In this test, we deliberately serve a bad signature initially. The
-    // subsequent signature returned is a valid one for the three item
-    // collection.
-    "GET:/v1/buckets/main/collections/signed?_expected=5000": [
-      RESPONSE_META_BAD_SIG,
-      RESPONSE_META_THREE_ITEMS_SIG,
-    ],
     // The first collection state is the three item collection (since
-    // there's a sync with no updates) - but, since the signature is wrong,
+    // there was sync with no updates before) - but, since the signature is wrong,
     // another request will be made...
-    "GET:/v1/buckets/main/collections/signed/records?_expected=5000&_sort=-last_modified&_since=4000": [
-      RESPONSE_EMPTY_NO_UPDATE,
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=5000&_since=4000": [
+      RESPONSE_EMPTY_NO_UPDATE_BAD_SIG,
     ],
-    // The next request is for the full collection. This will be checked against the valid signature
-    // - so the sync should succeed.
-    "GET:/v1/buckets/main/collections/signed/records?_expected=5000&_sort=-last_modified": [
+    // Subsequent signature returned is a valid one for the three item
+    // collection.
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=5000": [
       RESPONSE_COMPLETE_INITIAL,
     ],
   };
@@ -558,23 +524,16 @@ add_task(async function test_check_synchronization_with_signatures() {
   //   - Sync will be no-op since local is equal to server, no changes to emit.
 
   const badSigGoodOldResponses = {
-    // In this test, we deliberately serve a bad signature initially. The
-    // subsequent sitnature returned is a valid one for the three item
-    // collection.
-    "GET:/v1/buckets/main/collections/signed?_expected=5000": [
-      RESPONSE_META_BAD_SIG,
-      RESPONSE_META_EMPTY_SIG,
-    ],
     // The first collection state is the current state (since there's no update
     // - but, since the signature is wrong, another request will be made)
-    "GET:/v1/buckets/main/collections/signed/records?_expected=5000&_sort=-last_modified&_since=4000": [
-      RESPONSE_EMPTY_NO_UPDATE,
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=5000&_since=4000": [
+      RESPONSE_EMPTY_NO_UPDATE_BAD_SIG,
     ],
     // The next request is for the full collection. This will be
     // checked against the valid signature and last_modified times will be
     // compared. Sync should be a no-op, even though the signature is good,
     // because the local collection is newer.
-    "GET:/v1/buckets/main/collections/signed/records?_expected=5000&_sort=-last_modified": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=5000": [
       RESPONSE_EMPTY_INITIAL,
     ],
   };
@@ -603,17 +562,23 @@ add_task(async function test_check_synchronization_with_signatures() {
   // Check that a tampered local DB will be overwritten and
   // sync event contain the appropriate data.
 
+  const RESPONSE_COMPLETE_BAD_SIG = {
+    ...RESPONSE_EMPTY_NO_UPDATE,
+    responseBody: JSON.stringify({
+      timestamp: 5000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: "aW52YWxpZCBzaWduYXR1cmUK",
+        },
+      },
+      changes: [RECORD2, RECORD3],
+    }),
+  };
+
   const badLocalContentGoodSigResponses = {
-    // In this test, we deliberately serve a bad signature initially. The
-    // subsequent signature returned is a valid one for the three item
-    // collection.
-    "GET:/v1/buckets/main/collections/signed?_expected=5000": [
-      RESPONSE_META_BAD_SIG,
-      RESPONSE_META_THREE_ITEMS_SIG,
-    ],
-    // The next request is for the full collection. This will be checked
-    // against the valid signature - so the sync should succeed.
-    "GET:/v1/buckets/main/collections/signed/records?_expected=5000&_sort=-last_modified": [
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=5000": [
+      RESPONSE_COMPLETE_BAD_SIG,
       RESPONSE_COMPLETE_INITIAL,
     ],
   };
@@ -659,7 +624,7 @@ add_task(async function test_check_synchronization_with_signatures() {
   // Check that a failing signature throws after retry, and that sync changes
   // are not applied.
 
-  const RESPONSE_ONLY_RECORD4 = {
+  const RESPONSE_ONLY_RECORD4_BAD_SIG = {
     comment: "Delete RECORD3, create RECORD4",
     sampleHeaders: [
       "Content-Type: application/json; charset=UTF-8",
@@ -667,7 +632,14 @@ add_task(async function test_check_synchronization_with_signatures() {
     ],
     status: { status: 200, statusText: "OK" },
     responseBody: JSON.stringify({
-      data: [
+      timestamp: 6000,
+      metadata: {
+        signature: {
+          x5u,
+          signature: "wrong-sig-here-too",
+        },
+      },
+      changes: [
         {
           id: "f765df30-b2f1-42f6-9803-7bd5a07b5098",
           last_modified: 6000,
@@ -676,19 +648,11 @@ add_task(async function test_check_synchronization_with_signatures() {
     }),
   };
   const allBadSigResponses = {
-    // In this test, we deliberately serve only a bad signature.
-    "GET:/v1/buckets/main/collections/signed?_expected=6000": [
-      RESPONSE_META_BAD_SIG,
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=6000&_since=4000": [
+      RESPONSE_EMPTY_NO_UPDATE_BAD_SIG,
     ],
-    // The first collection state is the three item collection (since
-    // there's a sync with no updates) - but, since the signature is wrong,
-    // another request will be made...
-    "GET:/v1/buckets/main/collections/signed/records?_expected=6000&_sort=-last_modified&_since=4000": [
-      RESPONSE_EMPTY_NO_UPDATE,
-    ],
-    // The next request is for the full collection.
-    "GET:/v1/buckets/main/collections/signed/records?_expected=6000&_sort=-last_modified": [
-      RESPONSE_ONLY_RECORD4,
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=6000": [
+      RESPONSE_ONLY_RECORD4_BAD_SIG,
     ],
   };
 
@@ -747,24 +711,26 @@ add_task(async function test_check_synchronization_with_signatures() {
   //
   // Check that we don't apply changes when signature is missing in remote.
 
-  const RESPONSE_META_NO_SIG = {
+  const RESPONSE_NO_SIG = {
     sampleHeaders: [
       "Content-Type: application/json; charset=UTF-8",
       `ETag: \"123456\"`,
     ],
     status: { status: 200, statusText: "OK" },
     responseBody: JSON.stringify({
-      data: {
+      metadata: {
         last_modified: 123456,
       },
+      changes: [],
+      timestamp: 123456,
     }),
   };
 
   const missingSigResponses = {
     // In this test, we deliberately serve metadata without the signature attribute.
     // As if the collection was not signed.
-    "GET:/v1/buckets/main/collections/signed?_expected=6000": [
-      RESPONSE_META_NO_SIG,
+    "GET:/v1/buckets/main/collections/signed/changeset?_expected=6000": [
+      RESPONSE_NO_SIG,
     ],
   };