diff --git a/packages/SwingSet/src/controller.js b/packages/SwingSet/src/controller.js
index 4f0b38dab62..48081e194e4 100644
--- a/packages/SwingSet/src/controller.js
+++ b/packages/SwingSet/src/controller.js
@@ -59,7 +59,6 @@ export async function makeSwingsetController(
     slogCallbacks,
     slogFile,
     testTrackDecref,
-    defaultManagerType = env.WORKER_TYPE || 'local',
   } = runtimeOptions;
   if (typeof Compartment === 'undefined') {
     throw Error('SES must be installed before calling makeSwingsetController');
@@ -230,7 +229,7 @@ export async function makeSwingsetController(
     FinalizationRegistry,
   };
 
-  const kernelOptions = { verbose, testTrackDecref, defaultManagerType };
+  const kernelOptions = { verbose, testTrackDecref };
   const kernel = buildKernel(kernelEndowments, deviceEndowments, kernelOptions);
 
   if (runtimeOptions.verbose) {
@@ -324,14 +323,12 @@ export async function buildVatController(
     debugPrefix,
     slogCallbacks,
     testTrackDecref,
-    defaultManagerType,
   } = runtimeOptions;
   const actualRuntimeOptions = {
     verbose,
     debugPrefix,
     testTrackDecref,
     slogCallbacks,
-    defaultManagerType,
   };
   const initializationOptions = { verbose, kernelBundles };
   let bootstrapResult;
diff --git a/packages/SwingSet/src/initializeSwingset.js b/packages/SwingSet/src/initializeSwingset.js
index b9e1e48c799..2bb94bd45cb 100644
--- a/packages/SwingSet/src/initializeSwingset.js
+++ b/packages/SwingSet/src/initializeSwingset.js
@@ -1,4 +1,4 @@
-/* global require */
+/* global require, process */
 // @ts-check
 import fs from 'fs';
 import path from 'path';
@@ -75,6 +75,7 @@ function byName(a, b) {
 /**
  * @typedef {Object} SwingSetConfig a swingset config object
  * @property {string} [bootstrap]
+ * @property { ManagerType } [defaultManagerType]
  * @property {SwingSetConfigDescriptor} [vats]
  * @property {SwingSetConfigDescriptor} [bundles]
  * @property {*} [devices]
@@ -212,7 +213,6 @@ function normalizeConfigDescriptor(desc, dirname, expectParameters) {
  */
 export function loadSwingsetConfigFile(configPath) {
   try {
-    /** @type { SwingSetConfig } */
     const config = JSON.parse(fs.readFileSync(configPath, 'utf-8'));
     const dirname = path.dirname(configPath);
     normalizeConfigDescriptor(config.vats, dirname, true);
@@ -238,17 +238,18 @@ export function swingsetIsInitialized(storage) {
 }
 
 /**
- *
  * @param {SwingSetConfig} config
  * @param {string[]} argv
  * @param {*} hostStorage
  * @param {{ kernelBundles?: Record<string, string> }} initializationOptions
+ * @param {{ env?: Record<string, string> }} runtimeOptions
  */
 export async function initializeSwingset(
   config,
   argv = [],
   hostStorage = initSwingStore().storage,
   initializationOptions = {},
+  runtimeOptions = {},
 ) {
   insistStorageAPI(hostStorage);
 
@@ -269,6 +270,23 @@ export async function initializeSwingset(
     config.devices = {};
   }
 
+  // Use ambient process.env only if caller did not specify.
+  const { env: { WORKER_TYPE } = process.env } = runtimeOptions;
+  const defaultManagerType = config.defaultManagerType || WORKER_TYPE;
+  switch (defaultManagerType) {
+    case 'local':
+    case 'nodeWorker':
+    case 'node-subprocess':
+    case 'xs-worker':
+      config.defaultManagerType = defaultManagerType;
+      break;
+    case undefined:
+      config.defaultManagerType = 'local';
+      break;
+    default:
+      assert.fail(X`unknown manager type ${defaultManagerType}`);
+  }
+
   const { kernelBundles = await buildKernelBundles() } = initializationOptions;
 
   hostStorage.set('kernelBundle', JSON.stringify(kernelBundles.kernel));
diff --git a/packages/SwingSet/src/kernel/initializeKernel.js b/packages/SwingSet/src/kernel/initializeKernel.js
index 39c990ba346..105325260af 100644
--- a/packages/SwingSet/src/kernel/initializeKernel.js
+++ b/packages/SwingSet/src/kernel/initializeKernel.js
@@ -24,7 +24,7 @@ export function initializeKernel(config, hostStorage, verbose = false) {
 
   const wasInitialized = kernelKeeper.getInitialized();
   assert(!wasInitialized);
-  kernelKeeper.createStartingKernelState();
+  kernelKeeper.createStartingKernelState(config.defaultManagerType || 'local');
 
   if (config.bundles) {
     for (const name of Object.keys(config.bundles)) {
@@ -68,6 +68,9 @@ export function initializeKernel(config, hostStorage, verbose = false) {
       creationOptions.vatParameters = vatParameters;
       creationOptions.description = `static name=${name}`;
       creationOptions.name = name;
+      if (!creationOptions.managerType) {
+        creationOptions.managerType = kernelKeeper.getDefaultManagerType();
+      }
 
       const vatID = kernelKeeper.allocateVatIDForNameIfNeeded(name);
       logStartup(`assigned VatID ${vatID} for genesis vat ${name}`);
diff --git a/packages/SwingSet/src/kernel/loadVat.js b/packages/SwingSet/src/kernel/loadVat.js
index fe1f4646244..542e345efd6 100644
--- a/packages/SwingSet/src/kernel/loadVat.js
+++ b/packages/SwingSet/src/kernel/loadVat.js
@@ -33,6 +33,12 @@ export function makeVatLoader(stuff) {
     const vatID = allocateUnusedVatID();
     kernelKeeper.addDynamicVatID(vatID);
     const vatKeeper = kernelKeeper.allocateVatKeeper(vatID);
+    if (!dynamicOptions.managerType) {
+      dynamicOptions = {
+        ...dynamicOptions,
+        managerType: kernelKeeper.getDefaultManagerType(),
+      };
+    }
     vatKeeper.setSourceAndOptions(source, dynamicOptions);
     // eslint-disable-next-line no-use-before-define
     create(vatID, source, dynamicOptions, true, true);
diff --git a/packages/SwingSet/src/kernel/state/kernelKeeper.js b/packages/SwingSet/src/kernel/state/kernelKeeper.js
index 510a4cf0e21..6dd0860187a 100644
--- a/packages/SwingSet/src/kernel/state/kernelKeeper.js
+++ b/packages/SwingSet/src/kernel/state/kernelKeeper.js
@@ -198,7 +198,10 @@ export default function makeKernelKeeper(storage, kernelSlog) {
     storage.set('crankNumber', `${crankNumber + 1n}`);
   }
 
-  function createStartingKernelState() {
+  /**
+   * @param { ManagerType } defaultManagerType
+   */
+  function createStartingKernelState(defaultManagerType) {
     storage.set('vat.names', '[]');
     storage.set('vat.dynamicIDs', '[]');
     storage.set('vat.nextID', `${FIRST_VAT_ID}`);
@@ -209,6 +212,11 @@ export default function makeKernelKeeper(storage, kernelSlog) {
     storage.set('kp.nextID', `${FIRST_PROMISE_ID}`);
     storage.set('runQueue', JSON.stringify([]));
     storage.set('crankNumber', `${FIRST_CRANK_NUMBER}`);
+    storage.set('kernel.defaultManagerType', defaultManagerType);
+  }
+
+  function getDefaultManagerType() {
+    return getRequired('kernel.defaultManagerType');
   }
 
   function addBundle(name, bundle) {
@@ -819,6 +827,7 @@ export default function makeKernelKeeper(storage, kernelSlog) {
     getInitialized,
     setInitialized,
     createStartingKernelState,
+    getDefaultManagerType,
     addBundle,
     getBundle,
 
diff --git a/packages/SwingSet/src/kernel/state/vatKeeper.js b/packages/SwingSet/src/kernel/state/vatKeeper.js
index 96a9730b2f4..22f4538f433 100644
--- a/packages/SwingSet/src/kernel/state/vatKeeper.js
+++ b/packages/SwingSet/src/kernel/state/vatKeeper.js
@@ -63,6 +63,8 @@ export function makeVatKeeper(
   insistVatID(vatID);
 
   function setSourceAndOptions(source, options) {
+    // take care with API change
+    assert(options.managerType, X`vat options missing managerType`);
     assert.typeof(source, 'object');
     assert(source.bundle || source.bundleName);
     assert.typeof(options, 'object');
diff --git a/packages/SwingSet/src/types.js b/packages/SwingSet/src/types.js
index 3492bbefd9d..ae5ac3e794d 100644
--- a/packages/SwingSet/src/types.js
+++ b/packages/SwingSet/src/types.js
@@ -17,8 +17,9 @@
  * TODO: metered...
  *
  * See validateManagerOptions() in factory.js
+ * @typedef { 'local' | 'nodeWorker' | 'node-subprocess' | 'xs-worker' } ManagerType
  * @typedef {{
- *   managerType: 'local' | 'nodeWorker' | 'node-subprocess' | 'xs-worker',
+ *   managerType: ManagerType,
  *   metered?: boolean,
  *   enableInternalMetering?: boolean,
  *   enableDisavow?: boolean,
diff --git a/packages/SwingSet/test/test-controller.js b/packages/SwingSet/test/test-controller.js
index 9d6633754f0..22b088eee0b 100644
--- a/packages/SwingSet/test/test-controller.js
+++ b/packages/SwingSet/test/test-controller.js
@@ -1,8 +1,9 @@
 /* global require __dirname */
+// eslint-disable-next-line import/order
 import { test } from '../tools/prepare-test-env-ava';
 
-// eslint-disable-next-line import/order
 import path from 'path';
+import { initSwingStore } from '@agoric/swing-store-simple';
 import { buildVatController, loadBasedir } from '../src/index';
 import { checkKT } from './util';
 
@@ -94,6 +95,36 @@ test('bootstrap', async t => {
   t.deepEqual(c.dump().log, ['bootstrap called']);
 });
 
+test('XS bootstrap', async t => {
+  const config = await loadBasedir(
+    path.resolve(__dirname, 'basedir-controller-2'),
+  );
+  config.defaultManagerType = 'xs-worker';
+  const hostStorage = initSwingStore().storage;
+  const c = await buildVatController(config, [], { hostStorage });
+  t.deepEqual(c.dump().log, ['bootstrap called']);
+  t.is(
+    hostStorage.get('kernel.defaultManagerType'),
+    'xs-worker',
+    'defaultManagerType is saved by kernelKeeper',
+  );
+  const vatID = c.vatNameToID('bootstrap');
+  const options = JSON.parse(hostStorage.get(`${vatID}.options`));
+  t.is(
+    options.managerType,
+    'xs-worker',
+    'managerType gets recorded for the bootstrap vat',
+  );
+});
+
+test('validate config.defaultManagerType', async t => {
+  const config = await loadBasedir(
+    path.resolve(__dirname, 'basedir-controller-2'),
+  );
+  config.defaultManagerType = 'XYZ';
+  await t.throwsAsync(buildVatController(config), { message: /XYZ/ });
+});
+
 test('bootstrap export', async t => {
   const config = await loadBasedir(
     path.resolve(__dirname, 'basedir-controller-3'),
diff --git a/packages/SwingSet/test/test-kernel.js b/packages/SwingSet/test/test-kernel.js
index e5afefefd68..39beeb9aa09 100644
--- a/packages/SwingSet/test/test-kernel.js
+++ b/packages/SwingSet/test/test-kernel.js
@@ -1229,3 +1229,13 @@ test('pipelined promise queueing', async t => {
     },
   ]);
 });
+
+test('xs-worker default manager type', async t => {
+  const endowments = makeEndowments();
+  initializeKernel({ defaultManagerType: 'xs-worker' }, endowments.hostStorage);
+  buildKernel(endowments, {}, {});
+  t.deepEqual(
+    endowments.hostStorage.get('kernel.defaultManagerType'),
+    'xs-worker',
+  );
+});
diff --git a/packages/SwingSet/test/test-state.js b/packages/SwingSet/test/test-state.js
index 304c17fb7eb..defd3c98d5c 100644
--- a/packages/SwingSet/test/test-state.js
+++ b/packages/SwingSet/test/test-state.js
@@ -271,7 +271,7 @@ test('kernel state', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
   t.truthy(!k.getInitialized());
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
   k.setInitialized();
 
   commitCrank();
@@ -287,13 +287,14 @@ test('kernel state', async t => {
     ['ko.nextID', '20'],
     ['kd.nextID', '30'],
     ['kp.nextID', '40'],
+    ['kernel.defaultManagerType', 'local'],
   ]);
 });
 
 test('kernelKeeper vat names', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const v1 = k.allocateVatIDForNameIfNeeded('vatname5');
   const v2 = k.allocateVatIDForNameIfNeeded('Frank');
@@ -314,6 +315,7 @@ test('kernelKeeper vat names', async t => {
     ['kp.nextID', '40'],
     ['vat.name.vatname5', 'v1'],
     ['vat.name.Frank', 'v2'],
+    ['kernel.defaultManagerType', 'local'],
   ]);
   t.deepEqual(k.getStaticVats(), [
     ['Frank', 'v2'],
@@ -334,7 +336,7 @@ test('kernelKeeper vat names', async t => {
 test('kernelKeeper device names', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const d7 = k.allocateDeviceIDForNameIfNeeded('devicename5');
   const d8 = k.allocateDeviceIDForNameIfNeeded('Frank');
@@ -355,6 +357,7 @@ test('kernelKeeper device names', async t => {
     ['kp.nextID', '40'],
     ['device.name.devicename5', 'd7'],
     ['device.name.Frank', 'd8'],
+    ['kernel.defaultManagerType', 'local'],
   ]);
   t.deepEqual(k.getDevices(), [
     ['Frank', 'd8'],
@@ -375,7 +378,7 @@ test('kernelKeeper device names', async t => {
 test('kernelKeeper runQueue', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   t.truthy(k.isRunQueueEmpty());
   t.is(k.getRunQueueLength(), 0);
@@ -411,7 +414,7 @@ test('kernelKeeper runQueue', async t => {
 test('kernelKeeper promises', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const p1 = k.addKernelPromiseForVat('v4');
   t.deepEqual(k.getKernelPromise(p1), {
@@ -519,13 +522,14 @@ test('kernelKeeper promises', async t => {
     ['kp40.data.slots', 'ko44'],
     ['kp40.state', 'fulfilled'],
     ['kp40.refCount', '0'],
+    ['kernel.defaultManagerType', 'local'],
   ]);
 });
 
 test('kernelKeeper promise resolveToData', async t => {
   const { kstorage } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const p1 = k.addKernelPromiseForVat('v4');
   const capdata = harden({
@@ -546,7 +550,7 @@ test('kernelKeeper promise resolveToData', async t => {
 test('kernelKeeper promise reject', async t => {
   const { kstorage } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const p1 = k.addKernelPromiseForVat('v4');
   const capdata = harden({
@@ -567,7 +571,7 @@ test('kernelKeeper promise reject', async t => {
 test('vatKeeper', async t => {
   const { kstorage, getState, commitCrank } = buildKeeperStorageInMemory();
   const k = makeKernelKeeper(kstorage);
-  k.createStartingKernelState();
+  k.createStartingKernelState('local');
 
   const v1 = k.allocateVatIDForNameIfNeeded('name1');
   const vk = k.allocateVatKeeper(v1);
@@ -595,3 +599,10 @@ test('vatKeeper', async t => {
   t.is(vk2.mapKernelSlotToVatSlot(kernelImport2), vatImport2);
   t.is(vk2.mapVatSlotToKernelSlot(vatImport2), kernelImport2);
 });
+
+test('XS vatKeeper defaultManagerType', async t => {
+  const { kstorage } = buildKeeperStorageInMemory();
+  const k = makeKernelKeeper(kstorage);
+  k.createStartingKernelState('xs-worker');
+  t.is(k.getDefaultManagerType(), 'xs-worker');
+});