diff --git a/kits/bigquery-firestore-export/src/dts.ts b/kits/bigquery-firestore-export/src/dts.ts
index 5f509b360..1129e48bf 100644
--- a/kits/bigquery-firestore-export/src/dts.ts
+++ b/kits/bigquery-firestore-export/src/dts.ts
@@ -65,10 +65,16 @@ function stringField(value: string | undefined): { stringValue: string } {
   return { stringValue: value ?? "" };
 }
 
-/** Creates the protobuf-shaped request used for a scheduled query. */
+/**
+ * Creates the protobuf-shaped request used for a scheduled query.
+ *
+ * The query runs as whichever identity creates it, which is this function. To
+ * name a different account, `serviceAccountName` goes on the request rather
+ * than on the transfer config, and the caller needs `actAs` on the account it
+ * names, including its own.
+ */
 export function createTransferConfigRequest(
-  config: ResolvedBigqueryFirestoreExportConfig,
-  serviceAccountEmail?: string
+  config: ResolvedBigqueryFirestoreExportConfig
 ): bigqueryDataTransfer.protos.google.cloud.bigquery.datatransfer.v1.ICreateTransferConfigRequest {
   return {
     parent: `projects/${config.projectId}`,
@@ -88,9 +94,6 @@ export function createTransferConfigRequest(
       },
       schedule: config.schedule,
       notificationPubsubTopic: `projects/${config.projectId}/topics/${config.pubSubTopic}`,
-      ...(serviceAccountEmail
-        ? { serviceAccountName: serviceAccountEmail }
-        : {}),
     },
   };
 }
@@ -120,7 +123,7 @@ export async function createTransferConfig(
 ): Promise<TransferConfig> {
   logs.createTransferConfig();
   const [created] = await client.createTransferConfig(
-    createTransferConfigRequest(config, config.serviceAccount)
+    createTransferConfigRequest(config)
   );
   if (!created.name) {
     throw new Error("BigQuery API returned a transfer config without a name");
diff --git a/kits/bigquery-firestore-export/src/export-config.ts b/kits/bigquery-firestore-export/src/export-config.ts
index c39f434d3..6718bb67e 100644
--- a/kits/bigquery-firestore-export/src/export-config.ts
+++ b/kits/bigquery-firestore-export/src/export-config.ts
@@ -45,8 +45,6 @@ export interface BigqueryFirestoreExportConfig {
   pubSubTopic?: string;
   /** Root Firestore collection for configs and run output. */
   firestoreCollection?: string;
-  /** Runtime identity used when creating a DTS config. */
-  serviceAccount?: string;
   /** Log verbosity. Defaults to `info`. */
   logLevel?: LogLevel;
 }
@@ -65,7 +63,6 @@ export interface ResolvedBigqueryFirestoreExportConfig {
   schedule: string;
   pubSubTopic: string;
   firestoreCollection: string;
-  serviceAccount?: string;
   logLevel: LogLevel;
 }
 
@@ -117,7 +114,6 @@ export function resolveConfig(
       optional(config.pubSubTopic) ?? `kit-${instanceId}-processMessages`,
     firestoreCollection:
       optional(config.firestoreCollection) ?? "transferConfigs",
-    serviceAccount: optional(config.serviceAccount),
     logLevel,
   };
 }
diff --git a/kits/bigquery-firestore-export/tests/dts.test.ts b/kits/bigquery-firestore-export/tests/dts.test.ts
index 060ff3ae3..0e54b1bb0 100644
--- a/kits/bigquery-firestore-export/tests/dts.test.ts
+++ b/kits/bigquery-firestore-export/tests/dts.test.ts
@@ -43,10 +43,7 @@ function clientWithTransferConfig(transferConfig: object): DataTransferClient {
 
 describe("createTransferConfigRequest", () => {
   test("creates the scheduled-query request", () => {
-    const request = createTransferConfigRequest(
-      config,
-      "runtime@test-project.iam.gserviceaccount.com"
-    );
+    const request = createTransferConfigRequest(config);
 
     expect(request).toMatchObject({
       parent: "projects/test-project",
@@ -57,7 +54,6 @@ describe("createTransferConfigRequest", () => {
         schedule: "every 24 hours",
         notificationPubsubTopic:
           "projects/test-project/topics/kit-users-export-processMessages",
-        serviceAccountName: "runtime@test-project.iam.gserviceaccount.com",
       },
     });
     expect(
diff --git a/kits/bigquery-firestore-export/tests/export-config.test.ts b/kits/bigquery-firestore-export/tests/export-config.test.ts
index 728ae2883..d28ebb9f6 100644
--- a/kits/bigquery-firestore-export/tests/export-config.test.ts
+++ b/kits/bigquery-firestore-export/tests/export-config.test.ts
@@ -46,16 +46,12 @@ describe("resolveConfig", () => {
       ...minimal,
       transferConfigName: "  projects/p/locations/us/transferConfigs/c  ",
       partitioningField: "  created_at  ",
-      serviceAccount: "  runtime@test-project.iam.gserviceaccount.com  ",
     });
 
     expect(resolved.transferConfigName).toBe(
       "projects/p/locations/us/transferConfigs/c"
     );
     expect(resolved.partitioningField).toBe("created_at");
-    expect(resolved.serviceAccount).toBe(
-      "runtime@test-project.iam.gserviceaccount.com"
-    );
   });
 
   test.each(["instanceId", "datasetId", "tableName", "queryString"] as const)(