diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 159b12f8ae6d..2f1210cd5f93 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -1007,8 +1007,16 @@ zpool_do_add(int argc, char **argv)
 			*propval = '\0';
 			propval++;
 
-			if ((strcmp(optarg, ZPOOL_CONFIG_ASHIFT) != 0) ||
-			    (add_prop_list(optarg, propval, &props, B_TRUE)))
+			/* Only the following properties are allowed */
+			if ((strcmp(optarg,
+			    ZPOOL_CONFIG_ASHIFT) != 0) &&
+			    (strcmp(optarg,
+			    ZPOOL_PROP_OBJ_ENDPOINT_URI) != 0) &&
+			    (strcmp(optarg,
+			    ZPOOL_PROP_OBJ_REGION_NAME) != 0))
+				usage(B_FALSE);
+
+			if (add_prop_list(optarg, propval, &props, B_TRUE))
 				usage(B_FALSE);
 			break;
 		case 'P':
diff --git a/contrib/pyzfs/libzfs_core/_constants.py b/contrib/pyzfs/libzfs_core/_constants.py
index d4135041585a..b6fb30b9c20b 100644
--- a/contrib/pyzfs/libzfs_core/_constants.py
+++ b/contrib/pyzfs/libzfs_core/_constants.py
@@ -104,6 +104,8 @@ def enum(*sequential, **named):
         'ZFS_ERR_NOT_USER_NAMESPACE',
         'ZFS_ERR_RESUME_EXISTS',
         'ZFS_ERR_CRYPTO_NOTSUP',
+        'ZFS_ERR_OBJSTORE_EXISTS',
+        'ZFS_ERR_OBJSTORE_SINGLE_ADD',
     ],
     {}
 )
diff --git a/include/libzfs.h b/include/libzfs.h
index 029501f1c533..ed0fd6540eea 100644
--- a/include/libzfs.h
+++ b/include/libzfs.h
@@ -153,6 +153,8 @@ typedef enum zfs_error {
 	EZFS_NOT_USER_NAMESPACE,	/* a file is not a user namespace */
 	EZFS_CKSUM,		/* insufficient replicas */
 	EZFS_RESUME_EXISTS,	/* Resume on existing dataset without force */
+	EZFS_OBJSTORE_EXISTS, /* pool is already backed by an object store */
+	EZFS_OBJSTORE_ADD_ALONE, /* can't add extra vdevs with objstore */
 	EZFS_UNKNOWN
 } zfs_error_t;
 
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index 0968f0d3562d..56775748b1f6 100644
--- a/include/sys/fs/zfs.h
+++ b/include/sys/fs/zfs.h
@@ -725,6 +725,17 @@ typedef struct zpool_load_policy {
 #define	ZPOOL_CONFIG_VDEV_STATS		"vdev_stats"	/* not stored on disk */
 #define	ZPOOL_CONFIG_INDIRECT_SIZE	"indirect_size"	/* not stored on disk */
 
+/*
+ * These are user-visible property names that are specific to the object
+ * store. We declare those here because they happen to be temporarily
+ * added to the config in-memory, but they're never actually saved on
+ * disk with the config.
+ */
+#define	ZPOOL_PROP_OBJ_PROTOCOL_NAME	"object-protocol"
+#define	ZPOOL_PROP_OBJ_ENDPOINT_URI	"object-endpoint"
+#define	ZPOOL_PROP_OBJ_REGION_NAME	"object-region"
+#define	ZPOOL_PROP_OBJ_CRED_PROFILE_REF	"object-credentials-profile"
+
 /* container nvlist of extended stats */
 #define	ZPOOL_CONFIG_VDEV_STATS_EX	"vdev_stats_ex"
 
@@ -1571,6 +1582,8 @@ typedef enum {
 	ZFS_ERR_NOT_USER_NAMESPACE,
 	ZFS_ERR_RESUME_EXISTS,
 	ZFS_ERR_CRYPTO_NOTSUP,
+	ZFS_ERR_OBJSTORE_EXISTS,
+	ZFS_ERR_OBJSTORE_ADD_ALONE,
 } zfs_errno_t;
 
 /*
diff --git a/include/sys/spa_impl.h b/include/sys/spa_impl.h
index 674f68fc5265..c1c0aaf5224a 100644
--- a/include/sys/spa_impl.h
+++ b/include/sys/spa_impl.h
@@ -469,7 +469,8 @@ extern int param_set_deadman_failmode_common(const char *val);
 extern void spa_set_deadman_synctime(hrtime_t ns);
 extern void spa_set_deadman_ziotime(hrtime_t ns);
 extern const char *spa_history_zone(void);
-extern void spa_set_pool_type(spa_t *);
+extern void spa_set_pool_type_from_vdev_tree(spa_t *);
+extern void spa_set_pool_type_from_vdev_metadata(spa_t *);
 
 #ifdef	__cplusplus
 }
diff --git a/include/sys/vdev.h b/include/sys/vdev.h
index 4a6071742909..6606c871cd5d 100644
--- a/include/sys/vdev.h
+++ b/include/sys/vdev.h
@@ -69,6 +69,7 @@ extern int vdev_validate_aux(vdev_t *vd);
 extern zio_t *vdev_probe(vdev_t *vd, zio_t *pio);
 extern boolean_t vdev_is_concrete(vdev_t *vd);
 extern boolean_t vdev_is_object_based(vdev_t *vd);
+extern boolean_t vdev_is_object_store(vdev_t *vd);
 extern boolean_t vdev_is_bootable(vdev_t *vd);
 extern vdev_t *vdev_lookup_top(spa_t *spa, uint64_t vdev);
 extern vdev_t *vdev_lookup_by_guid(vdev_t *vd, uint64_t guid);
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index b482cc3615d3..0cd319d5eec4 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -307,6 +307,12 @@ libzfs_error_description(libzfs_handle_t *hdl)
 	case EZFS_RESUME_EXISTS:
 		return (dgettext(TEXT_DOMAIN, "Resuming recv on existing "
 		    "dataset without force"));
+	case EZFS_OBJSTORE_EXISTS:
+		return (dgettext(TEXT_DOMAIN, "pool already has an "
+		    "object store vdev"));
+	case EZFS_OBJSTORE_ADD_ALONE:
+		return (dgettext(TEXT_DOMAIN, "one vdev entry allowed "
+		    "when adding an object store vdev"));
 	case EZFS_UNKNOWN:
 		return (dgettext(TEXT_DOMAIN, "unknown error"));
 	default:
@@ -753,6 +759,12 @@ zpool_standard_error_fmt(libzfs_handle_t *hdl, int error, const char *fmt, ...)
 	case ZFS_ERR_IOC_ARG_BADTYPE:
 		zfs_verror(hdl, EZFS_IOC_NOTSUPPORTED, fmt, ap);
 		break;
+	case ZFS_ERR_OBJSTORE_EXISTS:
+		zfs_verror(hdl, EZFS_OBJSTORE_EXISTS, fmt, ap);
+		break;
+	case ZFS_ERR_OBJSTORE_ADD_ALONE:
+		zfs_verror(hdl, EZFS_OBJSTORE_ADD_ALONE, fmt, ap);
+		break;
 	default:
 		zfs_error_aux(hdl, "%s", strerror(error));
 		zfs_verror(hdl, EZFS_UNKNOWN, fmt, ap);
diff --git a/lib/libzutil/zutil_import.c b/lib/libzutil/zutil_import.c
index 5dfe63e41bde..3be238270ad6 100644
--- a/lib/libzutil/zutil_import.c
+++ b/lib/libzutil/zutil_import.c
@@ -1761,12 +1761,11 @@ zpool_find_import_cached(libpc_handle_t *hdl, importargs_t *iarg)
 			return (NULL);
 		}
 
-		nvlist_t *tree;
-		uint_t c, children;
-		nvlist_t **child;
-
-		tree = fnvlist_lookup_nvlist(src, ZPOOL_CONFIG_VDEV_TREE);
+		nvlist_t *tree =
+		    fnvlist_lookup_nvlist(src, ZPOOL_CONFIG_VDEV_TREE);
 
+		uint_t children;
+		nvlist_t **child;
 		if (nvlist_lookup_nvlist_array(tree, ZPOOL_CONFIG_CHILDREN,
 		    &child, &children) != 0) {
 			fprintf(stderr, gettext("cannot import '%s': invalid "
@@ -1775,7 +1774,7 @@ zpool_find_import_cached(libpc_handle_t *hdl, importargs_t *iarg)
 		}
 
 		boolean_t object_store_pool_found = B_FALSE;
-		for (c = 0; c < children; c++) {
+		for (uint_t c = 0; c < children; c++) {
 			const char *type;
 			if (nvlist_lookup_string(child[c], ZPOOL_CONFIG_TYPE,
 			    &type) != 0) {
@@ -1848,11 +1847,14 @@ zpool_find_import_agent(libpc_handle_t *hdl, importargs_t *iarg,
 	if (bucket == NULL && iarg->path != NULL) {
 		bucket = iarg->path[0];
 	}
-	nvlist_lookup_string(iarg->props, "object-protocol", &protocol);
-	nvlist_lookup_string(iarg->props, "object-endpoint", &endpoint);
-	nvlist_lookup_string(iarg->props, "object-region", &region);
-	nvlist_lookup_string(iarg->props, "object-credentials-profile",
-	    &profile);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_PROTOCOL_NAME, &protocol);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_ENDPOINT_URI, &endpoint);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_REGION_NAME, &region);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_CRED_PROFILE_REF, &profile);
 
 	nvlist_t *msg = fnvlist_alloc();
 	fnvlist_add_string(msg, AGENT_REQUEST_TYPE, AGENT_TYPE_GET_POOLS);
@@ -1911,14 +1913,17 @@ zpool_find_import_agent(libpc_handle_t *hdl, importargs_t *iarg,
 		 * them to the config here.
 		 */
 		if (region != NULL)
-			fnvlist_add_string(tree, "object-region", region);
+			fnvlist_add_string(tree,
+			    ZPOOL_PROP_OBJ_REGION_NAME, region);
 		if (endpoint != NULL)
-			fnvlist_add_string(tree, "object-endpoint", endpoint);
+			fnvlist_add_string(tree,
+			    ZPOOL_PROP_OBJ_ENDPOINT_URI, endpoint);
 		if (protocol != NULL)
-			fnvlist_add_string(tree, "object-protocol", protocol);
+			fnvlist_add_string(tree,
+			    ZPOOL_PROP_OBJ_PROTOCOL_NAME, protocol);
 		if (profile != NULL)
-			fnvlist_add_string(tree, "object-credentials-profile",
-			    profile);
+			fnvlist_add_string(tree,
+			    ZPOOL_PROP_OBJ_CRED_PROFILE_REF, profile);
 
 		slice->rn_vdev_guid = guid;
 		slice->rn_lock = lock;
@@ -2161,11 +2166,14 @@ zoa_resume_destroy(void *hdl, importargs_t *iarg)
 	if (bucket == NULL) {
 		return (-1);
 	}
-	nvlist_lookup_string(iarg->props, "object-protocol", &protocol);
-	nvlist_lookup_string(iarg->props, "object-endpoint", &endpoint);
-	nvlist_lookup_string(iarg->props, "object-region", &region);
-	nvlist_lookup_string(iarg->props, "object-credentials-profile",
-	    &profile);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_PROTOCOL_NAME, &protocol);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_ENDPOINT_URI, &endpoint);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_REGION_NAME, &region);
+	nvlist_lookup_string(iarg->props,
+	    ZPOOL_PROP_OBJ_CRED_PROFILE_REF, &profile);
 
 	// Resume destroy
 	nvlist_t *msg = fnvlist_alloc();
diff --git a/module/os/freebsd/zfs/spa_os.c b/module/os/freebsd/zfs/spa_os.c
index 8505b021398b..f94ad2b627ab 100644
--- a/module/os/freebsd/zfs/spa_os.c
+++ b/module/os/freebsd/zfs/spa_os.c
@@ -246,7 +246,7 @@ spa_import_rootpool(const char *name, bool checkpointrewind)
 	spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
 	error = spa_config_parse(spa, &rvd, nvtop, NULL, 0,
 	    VDEV_ALLOC_ROOTPOOL);
-	spa_set_pool_type(spa);
+	spa_set_pool_type_from_vdev_metadata(spa);
 	spa_config_exit(spa, SCL_ALL, FTAG);
 	if (error) {
 		mutex_exit(&spa_namespace_lock);
diff --git a/module/os/linux/zfs/vdev_object_store.c b/module/os/linux/zfs/vdev_object_store.c
index 83222066d2bb..182fe38c0221 100644
--- a/module/os/linux/zfs/vdev_object_store.c
+++ b/module/os/linux/zfs/vdev_object_store.c
@@ -2403,7 +2403,18 @@ vdev_object_store_open(vdev_t *vd, uint64_t *psize, uint64_t *max_psize,
 	vos->vos_send_thread  = thread_create(NULL, 0,
 	    vdev_object_store_send_thread, vd, 0, &p0, TS_RUN, defclsyspri);
 
-	if (vd->vdev_spa->spa_load_state == SPA_LOAD_CREATE) {
+	/*
+	 * There are two cases where we want to create an "object-store pool":
+	 * [1] We are creating a brand new ZFS pool on top of an object store
+	 *     (e.g. SPA_LOAD_CREATE).
+	 * [2] We are about to add an object-based vdev as part of migrating a
+	 *     block-based ZFS pool to an object-based one (e.g. this is the
+	 *     spa_pending_vdev and the spa pool type is not object based yet).
+	 */
+	spa_t *spa = vd->vdev_spa;
+	if ((spa->spa_load_state == SPA_LOAD_CREATE) ||
+	    (vdev_is_object_based(spa->spa_pending_vdev) &&
+	    !spa_is_object_based(spa))) {
 		vos->vos_create_completed = B_FALSE;
 		error = object_store_create_pool(vd);
 		if (error != 0) {
diff --git a/module/zcommon/zpool_prop.c b/module/zcommon/zpool_prop.c
index 625bdcc2bf2e..b501c62aeee1 100644
--- a/module/zcommon/zpool_prop.c
+++ b/module/zcommon/zpool_prop.c
@@ -82,16 +82,20 @@ zpool_prop_init(void)
 	zprop_register_string(ZPOOL_PROP_COMPATIBILITY, "compatibility",
 	    "off", PROP_DEFAULT, ZFS_TYPE_POOL,
 	    "<file[,file...]> | off | legacy", "COMPATIBILITY", sfeatures);
-	zprop_register_string(ZPOOL_PROP_OBJ_PROTOCOL, "object-protocol", NULL,
-	    PROP_DEFAULT, ZFS_TYPE_POOL, "<protocol>", "OBJ_PROTOCOL",
-	    sfeatures);
-	zprop_register_string(ZPOOL_PROP_OBJ_ENDPOINT, "object-endpoint", NULL,
-	    PROP_DEFAULT, ZFS_TYPE_POOL, "<uri>", "OBJ_ENDPOINT", sfeatures);
-	zprop_register_string(ZPOOL_PROP_OBJ_REGION, "object-region", NULL,
-	    PROP_DEFAULT, ZFS_TYPE_POOL, "<region>", "OBJ_REGION", sfeatures);
+	zprop_register_string(ZPOOL_PROP_OBJ_PROTOCOL,
+	    ZPOOL_PROP_OBJ_PROTOCOL_NAME, NULL,
+	    PROP_DEFAULT, ZFS_TYPE_POOL, "<protocol>",
+	    "OBJ_PROTOCOL", sfeatures);
+	zprop_register_string(ZPOOL_PROP_OBJ_ENDPOINT,
+	    ZPOOL_PROP_OBJ_ENDPOINT_URI, NULL,
+	    PROP_DEFAULT, ZFS_TYPE_POOL, "<uri>",
+	    "OBJ_ENDPOINT", sfeatures);
+	zprop_register_string(ZPOOL_PROP_OBJ_REGION,
+	    ZPOOL_PROP_OBJ_REGION_NAME, NULL, PROP_DEFAULT, ZFS_TYPE_POOL,
+	    "<region>", "OBJ_REGION", sfeatures);
 	zprop_register_string(ZPOOL_PROP_OBJ_CRED_PROFILE,
-	    "object-credentials-profile", NULL, PROP_DEFAULT, ZFS_TYPE_POOL,
-	    "<profile>", "OBJ_CRED_PROFILE", sfeatures);
+	    ZPOOL_PROP_OBJ_CRED_PROFILE_REF, NULL, PROP_DEFAULT,
+	    ZFS_TYPE_POOL, "<profile>", "OBJ_CRED_PROFILE", sfeatures);
 
 	/* readonly number properties */
 	zprop_register_number(ZPOOL_PROP_SIZE, "size", 0, PROP_READONLY,
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 01e026e4e5e9..8f49c2a1c62d 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -3592,7 +3592,7 @@ spa_ld_parse_config(spa_t *spa, spa_import_type_t type)
 	parse = (type == SPA_IMPORT_EXISTING ?
 	    VDEV_ALLOC_LOAD : VDEV_ALLOC_SPLIT);
 	error = spa_config_parse(spa, &rvd, nvtree, NULL, 0, parse);
-	spa_set_pool_type(spa);
+	spa_set_pool_type_from_vdev_metadata(spa);
 	spa_config_exit(spa, SCL_ALL, FTAG);
 
 	if (error != 0) {
@@ -3964,7 +3964,7 @@ spa_ld_trusted_config(spa_t *spa, spa_import_type_t type,
 		    error);
 		return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, error));
 	}
-	spa_set_pool_type(spa);
+	spa_set_pool_type_from_vdev_metadata(spa);
 
 	/*
 	 * Vdev paths in the MOS may be obsolete. If the untrusted config was
@@ -4859,6 +4859,10 @@ spa_ld_checkpoint_rewind(spa_t *spa)
 			if (svdcount == SPA_SYNC_MIN_VDEVS)
 				break;
 		}
+
+		ASSERT(!spa_is_object_based(spa));
+		ASSERT(!vdev_is_object_based(spa->spa_root_vdev));
+
 		error = vdev_config_sync(svd, svdcount, spa->spa_first_txg);
 		if (error == 0)
 			spa->spa_last_synced_guid = rvd->vdev_guid;
@@ -6068,7 +6072,7 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 
 	error = spa_config_parse(spa, &rvd, nvroot, NULL, 0, VDEV_ALLOC_ADD);
 	if (error == 0)
-		spa_set_pool_type(spa);
+		spa_set_pool_type_from_vdev_tree(spa);
 
 	ASSERT(error != 0 || rvd != NULL);
 	ASSERT(error != 0 || spa->spa_root_vdev == rvd);
@@ -6414,6 +6418,11 @@ spa_import(char *pool, nvlist_t *config, nvlist_t *props, uint64_t flags)
 	if (spa_writeable(spa)) {
 		/*
 		 * Update the config cache to include the newly-imported pool.
+		 *
+		 * This may also create metaslabs for newly added vdevs (see
+		 * `spa_vdev_add()`. This normally happens through the async
+		 * thread request of `spa_ld_check_for_config_update()` calling
+		 * `spa_config_update()` but this code path may get there first.
 		 */
 		spa_config_update(spa, SPA_CONFIG_UPDATE_POOL);
 	}
@@ -6801,6 +6810,55 @@ spa_vdev_add(spa_t *spa, nvlist_t *nvroot)
 
 	spa->spa_pending_vdev = vd;	/* spa_vdev_exit() will clear this */
 
+	if (vdev_is_object_based(vd)) {
+		/*
+		 * Can't add a second object-store vdev to object-based
+		 * pool.
+		 *
+		 * Note: we check if there is an object-store vdev under the
+		 * root_vdev instead of using the `spa_is_object_based()`
+		 * helper because it is possible that we just added an object
+		 * store vdev in this pool but we haven't yet converted the
+		 * pool's type.
+		 */
+		if (vdev_is_object_based(spa->spa_root_vdev)) {
+			return (spa_vdev_exit(spa, vd, txg,
+			    SET_ERROR(ZFS_ERR_OBJSTORE_EXISTS)));
+		}
+
+		/*
+		 * If we are adding an object-store vdev to migrate a
+		 * block-based pool to the object store, ensure that
+		 * zpool-add just passed that vdev and nothing else.
+		 * This is a lazy way of making sure that we don't add
+		 * two object store vdevs at once. Note, it also
+		 * prevents us from adding any other type of vdev within
+		 * the same zpool-add invocation.
+		 */
+		if (vd->vdev_children > 1) {
+			return (spa_vdev_exit(spa, vd, txg,
+			    SET_ERROR(ZFS_ERR_OBJSTORE_ADD_ALONE)));
+		}
+
+		/*
+		 * Pure object-based pools (e.g. not hybrid ones) do the
+		 * checkpoint rewinding process in the object agent. This
+		 * is a different mechanism from the storage pool checkpoint
+		 * in block-based pools. Until we have the need to make those
+		 * two mechanism work well with each other we avoid any
+		 * migrations to the object store while a zpool checkpoint
+		 * is in effect. See `spa_ld_checkpoint_rewind()` usage in
+		 * `spa_load_impl()` for more info.
+		 */
+		if (spa_feature_is_active(spa, SPA_FEATURE_POOL_CHECKPOINT)) {
+			error = (spa_has_checkpoint(spa)) ?
+			    ZFS_ERR_CHECKPOINT_EXISTS :
+			    ZFS_ERR_DISCARDING_CHECKPOINT;
+			return (spa_vdev_exit(spa, NULL, txg,
+			    SET_ERROR(error)));
+		}
+	}
+
 	if (nvlist_lookup_nvlist_array(nvroot, ZPOOL_CONFIG_SPARES, &spares,
 	    &nspares) != 0)
 		nspares = 0;
@@ -8381,9 +8439,12 @@ spa_async_thread(void *arg)
 		uint64_t old_space, new_space;
 
 		mutex_enter(&spa_namespace_lock);
+		/*
+		 * There is no point in introducing the object store class
+		 * here as it would ruin any reasonable calculation for the
+		 * history log message below and won't be helpful in any way.
+		 */
 		old_space = metaslab_class_get_space(spa_normal_class(spa));
-		old_space +=
-		    metaslab_class_get_space(spa_object_store_class(spa));
 		old_space += metaslab_class_get_space(spa_special_class(spa));
 		old_space += metaslab_class_get_space(spa_dedup_class(spa));
 		old_space += metaslab_class_get_space(
@@ -9566,7 +9627,8 @@ spa_sync(spa_t *spa, uint64_t txg)
 	VERIFY(spa_writeable(spa));
 
 	if (spa_is_object_based(spa)) {
-		object_store_begin_txg(spa->spa_root_vdev->vdev_child[0], txg);
+		object_store_begin_txg(vdev_find_leaf(spa->spa_root_vdev,
+		    &vdev_object_store_ops), txg);
 	}
 
 	/*
diff --git a/module/zfs/spa_config.c b/module/zfs/spa_config.c
index 0d2f9fa28be9..fea58291a4cf 100644
--- a/module/zfs/spa_config.c
+++ b/module/zfs/spa_config.c
@@ -618,6 +618,22 @@ spa_config_update(spa_t *spa, int what)
 		    what != SPA_CONFIG_UPDATE_POOL);
 	}
 
+	if (what == SPA_CONFIG_UPDATE_VDEVS) {
+		/*
+		 * If we recently added an object store vdev we need
+		 * to reset the pool's type. That needs to happen at
+		 * a point when that vdev is allocatable so we do it
+		 * here after creating its metaslab metadata above
+		 * and waiting for one TXG for them to sync to disk.
+		 */
+		spa_config_enter(spa, SCL_ALL, spa, RW_WRITER);
+		if (vdev_is_object_based(spa->spa_root_vdev) &&
+		    !spa_is_object_based(spa)) {
+			spa_set_pool_type_from_vdev_metadata(spa);
+		}
+		spa_config_exit(spa, SCL_ALL, spa);
+	}
+
 	if (what == SPA_CONFIG_UPDATE_POOL)
 		spa_config_update(spa, SPA_CONFIG_UPDATE_VDEVS);
 }
diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index eae2f87468c2..fcff6d08a555 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -432,8 +432,19 @@ static int zfs_user_indirect_is_special = B_TRUE;
  */
 static uint_t zfs_special_class_metadata_reserve_pct = 25;
 
+/*
+ * Set the pool's type based on whether the config contains an
+ * object store vdev or not. It does not check whether the object
+ * store vdev is allocatable. This makes this wrapper suitable
+ * only for the scenario of pool creation where there is no
+ * allocation metadata (e.g metaslabs) initialized yet for any
+ * device in the pool.
+ *
+ * To set the pool's type during import or device addition use
+ * `spa_set_pool_type_from_vdev_metadata()` instead.
+ */
 void
-spa_set_pool_type(spa_t *spa)
+spa_set_pool_type_from_vdev_tree(spa_t *spa)
 {
 	ASSERT3P(spa->spa_root_vdev, !=, NULL);
 
@@ -445,6 +456,32 @@ spa_set_pool_type(spa_t *spa)
 	    SPA_TYPE_OBJECT_STORE : SPA_TYPE_NORMAL;
 }
 
+/*
+ * Set the pool's type based on whether the config contains an
+ * object store vdev AND whether that vdev is allocatable or not.
+ */
+void
+spa_set_pool_type_from_vdev_metadata(spa_t *spa)
+{
+	ASSERT3P(spa->spa_root_vdev, !=, NULL);
+
+	/*
+	 * Must hold all of spa_config locks.
+	 */
+	ASSERT3U(spa_config_held(spa, SCL_ALL, RW_WRITER), ==, SCL_ALL);
+	vdev_t *object_store =
+	    vdev_find_leaf(spa->spa_root_vdev, &vdev_object_store_ops);
+
+	/*
+	 * Even if there is an object store vdev, it may not have a
+	 * metaslab array (i.e. it doesn't accept allocations yet).
+	 */
+	if (object_store == NULL || object_store->vdev_ms_array == 0)
+		spa->spa_pool_type = SPA_TYPE_NORMAL;
+	else
+		spa->spa_pool_type = SPA_TYPE_OBJECT_STORE;
+}
+
 boolean_t
 spa_is_object_based(spa_t *spa)
 {
diff --git a/module/zfs/vdev.c b/module/zfs/vdev.c
index 96069e44611f..5718987ba09f 100644
--- a/module/zfs/vdev.c
+++ b/module/zfs/vdev.c
@@ -1455,7 +1455,7 @@ vdev_metaslab_group_create(vdev_t *vd)
 		}
 
 		/*
-		 * The spa ashift min/max only apply for the normal metaslab
+		 * The spa ashift min/max only apply for the default metaslab
 		 * class. Class destination is late binding so ashift boundary
 		 * setting had to wait until now.
 		 */
@@ -5481,6 +5481,18 @@ vdev_is_object_based(vdev_t *vd)
 	return (object_based);
 }
 
+/*
+ * This predicate is similar to `vdev_is_object_based()` but only checks the
+ * vdev parameter passed to it and not any children under it. It also doesn't
+ * attempt to grab any config locks.
+ */
+boolean_t
+vdev_is_object_store(vdev_t *vd)
+{
+	return ((vd != NULL) ?
+	    (vd->vdev_ops == &vdev_object_store_ops) : B_FALSE);
+}
+
 /*
  * Determine if a log device has valid content.  If the vdev was
  * removed or faulted in the MOS config then we know that
diff --git a/module/zfs/vdev_label.c b/module/zfs/vdev_label.c
index 289b13f164dd..7d5df1e99aa1 100644
--- a/module/zfs/vdev_label.c
+++ b/module/zfs/vdev_label.c
@@ -1715,6 +1715,12 @@ vdev_uberblock_sync(zio_t *zio, uint64_t *good_writes,
 	if (!vd->vdev_ops->vdev_op_leaf)
 		return;
 
+	/*
+	 * Object store uberblock is written in `object_store_end_txg()`.
+	 */
+	if (vdev_is_object_store(vd))
+		return;
+
 	if (!vdev_writeable(vd))
 		return;
 
@@ -1751,15 +1757,33 @@ vdev_uberblock_sync(zio_t *zio, uint64_t *good_writes,
 	abd_free(ub_abd);
 }
 
-/* Sync the uberblocks to all vdevs in svd[] */
+/*
+ * Sync the uberblocks to the object store vdev (if it exists)
+ * and all vdevs in svd[].
+ */
 static int
 vdev_uberblock_sync_list(vdev_t **svd, int svdcount, uberblock_t *ub, int flags)
 {
 	spa_t *spa = svd[0]->vdev_spa;
-	zio_t *zio;
 	uint64_t good_writes = 0;
 
-	zio = zio_root(spa, NULL, NULL, flags);
+	/*
+	 * If this pool is using object storage, then we need to notify the
+	 * backend that we've completed the txg. This operation combines
+	 * syncing the uberblock/labels/config to the object store. We
+	 * always do this first as it's the object store's config that we'll
+	 * use to open the pool.
+	 */
+	if (spa_is_object_based(spa)) {
+		vdev_t *vd_os = vdev_find_leaf(spa->spa_root_vdev,
+		    &vdev_object_store_ops);
+		nvlist_t *label = spa_config_generate(spa,
+		    vd_os, ub->ub_txg, B_FALSE);
+		object_store_end_txg(vd_os, label, ub->ub_txg);
+		good_writes++;
+	}
+
+	zio_t *zio = zio_root(spa, NULL, NULL, flags);
 
 	for (int v = 0; v < svdcount; v++)
 		vdev_uberblock_sync(zio, &good_writes, ub, svd[v], flags);
@@ -1881,21 +1905,25 @@ static int
 vdev_label_sync_list(spa_t *spa, int l, uint64_t txg, int flags)
 {
 	list_t *dl = &spa->spa_config_dirty_list;
-	vdev_t *vd;
-	zio_t *zio;
-	int error;
 
 	/*
 	 * Write the new labels to disk.
 	 */
-	zio = zio_root(spa, NULL, NULL, flags);
-
-	for (vd = list_head(dl); vd != NULL; vd = list_next(dl, vd)) {
-		uint64_t *good_writes;
+	zio_t *zio = zio_root(spa, NULL, NULL, flags);
 
+	for (vdev_t *vd = list_head(dl); vd != NULL;
+	    vd = list_next(dl, vd)) {
 		ASSERT(!vd->vdev_ishole);
 
-		good_writes = kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
+		/*
+		 * Object store label is updated
+		 * in `object_store_end_txg()`.
+		 */
+		if (vdev_is_object_store(vd))
+			continue;
+
+		uint64_t *good_writes =
+		    kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
 		zio_t *vio = zio_null(zio, spa, NULL,
 		    (vd->vdev_islog || vd->vdev_aux != NULL) ?
 		    vdev_label_sync_ignore_done : vdev_label_sync_top_done,
@@ -1904,14 +1932,14 @@ vdev_label_sync_list(spa_t *spa, int l, uint64_t txg, int flags)
 		zio_nowait(vio);
 	}
 
-	error = zio_wait(zio);
+	int error = zio_wait(zio);
 
 	/*
 	 * Flush the new labels to disk.
 	 */
 	zio = zio_root(spa, NULL, NULL, flags);
 
-	for (vd = list_head(dl); vd != NULL; vd = list_next(dl, vd))
+	for (vdev_t *vd = list_head(dl); vd != NULL; vd = list_next(dl, vd))
 		zio_flush(zio, vd);
 
 	(void) zio_wait(zio);
@@ -1973,28 +2001,13 @@ vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
 		return (0);
 
 	/*
-	 * If this pool is using object storage, then
-	 * it only needs to notify the backend that
-	 * we've completed the txg and return.
+	 * Object-store pools may go past the spa_final_dirty_txg
+	 * (see comment in ub_dp_mos_used_delta for more).
 	 */
-	if (spa_is_object_based(spa)) {
-		/*
-		 * XXX - Right now we don't update the labels on
-		 * any slog devices if we're using object-based pools.
-		 * This seems to be fine since the mos config object
-		 * will have all the information we need. However, there
-		 * might be some corner cases where need to look at the
-		 * label on the slog device directly. If that is
-		 * the case, then we will need to revisit this.
-		 */
-		nvlist_t *label = spa_config_generate(spa,
-		    svd[0], txg, B_FALSE);
-		object_store_end_txg(svd[0], label, txg);
-		return (0);
+	if (!spa_is_object_based(spa)) {
+		ASSERT3U(txg, <=, spa_final_dirty_txg(spa));
 	}
 
-	ASSERT3U(txg, <=, spa_final_dirty_txg(spa));
-
 	/*
 	 * Flush the write cache of every disk that's been written to
 	 * in this transaction group.  This ensures that all blocks
@@ -2029,9 +2042,10 @@ vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
 	}
 
 	/*
-	 * Sync the uberblocks to all vdevs in svd[].
-	 * If the system dies in the middle of this step, there are two cases
-	 * to consider, and the on-disk state is consistent either way:
+	 * Sync the uberblocks to the object store vdev (if it exists) and
+	 * all the vdevs in svd[]. If the system dies in the middle of this
+	 * step, there are two cases to consider, and the on-disk state is
+	 * consistent either way:
 	 *
 	 * (1)	If none of the new uberblocks made it to disk, then the
 	 *	previous uberblock will be the newest, and the odd labels
@@ -2045,8 +2059,9 @@ vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
 	 */
 	if ((error = vdev_uberblock_sync_list(svd, svdcount, ub, flags)) != 0) {
 		if ((flags & ZIO_FLAG_TRYHARD) != 0) {
-			zfs_dbgmsg("vdev_uberblock_sync_list() returned error "
-			    "%d for pool '%s'", error, spa_name(spa));
+			zfs_dbgmsg("vdev_uberblock_sync_list() "
+			    "returned error %d for pool '%s'",
+			    error, spa_name(spa));
 		}
 		goto retry;
 	}
diff --git a/module/zfs/zil.c b/module/zfs/zil.c
index ba106a49bc49..01de74200d31 100644
--- a/module/zfs/zil.c
+++ b/module/zfs/zil.c
@@ -1602,6 +1602,7 @@ zil_lwb_write_done(zio_t *zio)
 	while ((zv = avl_destroy_nodes(t, &cookie)) != NULL) {
 		vdev_t *vd = vdev_lookup_top(spa, zv->zv_vdev);
 		if (vd != NULL) {
+			ASSERT(!vdev_is_object_store(vd));
 			/*
 			 * The "ZIO_FLAG_DONT_PROPAGATE" is currently
 			 * always used within "zio_flush". This means,
@@ -3324,6 +3325,14 @@ zil_commit(zilog_t *zilog, uint64_t foid)
 	if (zilog->zl_sync == ZFS_SYNC_DISABLED)
 		return;
 
+	/*
+	 * If this is an object store pool and we have no slog devices skip
+	 * committing this zil. Note, in a hybrid pool (e.g. backed by both
+	 * an object store and block devices) we could fall back to
+	 * allocating the zil from the normal/embedded_log class if there
+	 * are no slog devices. This functionality is left as potential
+	 * future work.
+	 */
 	if (spa_is_object_based(zilog->zl_spa) &&
 	    !spa_has_slogs(zilog->zl_spa)) {
 		ZIL_STAT_BUMP(zilog, zil_skip_zil_commit);
diff --git a/module/zfs/zio.c b/module/zfs/zio.c
index 910ce2177af8..62b47f461ef8 100644
--- a/module/zfs/zio.c
+++ b/module/zfs/zio.c
@@ -1545,6 +1545,13 @@ zio_vdev_delegated_io(vdev_t *vd, uint64_t offset, abd_t *data, uint64_t size,
 void
 zio_flush(zio_t *zio, vdev_t *vd)
 {
+	/*
+	 * Object store vdevs have their own mechanism for flushing
+	 * their changes to the backend - see `object_store_end_txg()`.
+	 */
+	if (vdev_is_object_store(vd))
+		return;
+
 	zio_nowait(zio_ioctl(zio, zio->io_spa, vd, DKIOCFLUSHWRITECACHE,
 	    NULL, NULL,
 	    ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY));
@@ -3802,22 +3809,16 @@ zio_alloc_zil(spa_t *spa, objset_t *os, uint64_t txg, blkptr_t *new_bp,
 	ASSERT3U(spa->spa_alloc_count, ==,
 	    metaslab_class_allocator_count(spa_embedded_log_class(spa)));
 
-	/*
-	 * Object-based pools can only allocate zil block on the slog,
-	 * so if we failed to allocate from the slog we need to return
-	 * an error and not fallback to the normal class.
-	 */
-	boolean_t object_based = spa_is_object_based(spa);
 	error = metaslab_alloc(spa, spa_log_class(spa), size, new_bp, 1,
 	    txg, NULL, flags, &io_alloc_list, NULL, allocator);
-	*slog = (error == 0 || object_based);
+	*slog = (error == 0);
 
-	if (error != 0 && !object_based) {
+	if (error != 0) {
 		error = metaslab_alloc(spa, spa_embedded_log_class(spa), size,
 		    new_bp, 1, txg, NULL, flags,
 		    &io_alloc_list, NULL, allocator);
 	}
-	if (error != 0 && !object_based) {
+	if (error != 0) {
 		error = metaslab_alloc(spa, spa_normal_class(spa), size,
 		    new_bp, 1, txg, NULL, flags,
 		    &io_alloc_list, NULL, allocator);
diff --git a/module/zfs/zio_inject.c b/module/zfs/zio_inject.c
index 0850f3f92b88..9a3f9441ffa9 100644
--- a/module/zfs/zio_inject.c
+++ b/module/zfs/zio_inject.c
@@ -180,8 +180,9 @@ zio_handle_panic_injection(spa_t *spa, const char *tag, uint64_t type)
 		if (handler->zi_record.zi_type == type &&
 		    strcmp(tag, handler->zi_record.zi_func) == 0) {
 			if (spa_is_object_based(spa)) {
-				vdev_t *vd = spa->spa_root_vdev->vdev_child[0];
-				object_store_restart_agent(vd);
+				object_store_restart_agent(
+				    vdev_find_leaf(spa->spa_root_vdev,
+				    &vdev_object_store_ops));
 			} else {
 				panic("Panic requested in function %s\n", tag);
 			}
diff --git a/tests/runfiles/object_store.run b/tests/runfiles/object_store.run
index 0de43bc1fcfb..d835aef13689 100644
--- a/tests/runfiles/object_store.run
+++ b/tests/runfiles/object_store.run
@@ -54,6 +54,14 @@ tests = ['checkpoint_after_rewind', 'checkpoint_big_rewind',
 tags = ['functional', 'pool_checkpoint']
 timeout = 1800
 
+[tests/functional/block_to_object]
+pre =
+post =
+tests = ['zpool_add', 'zpool_add_args_neg', 'zpool_add_ckpoint',
+    'zpool_add_existing', 'zpool_add_with_writes',
+    'hybrid_pool_import_export']
+tags = ['functional', 'block_to_object']
+
 [tests/functional/chattr]
 tests = ['chattr_001_pos', 'chattr_002_neg']
 tags = ['functional', 'chattr']
diff --git a/tests/zfs-tests/tests/functional/block_to_object/block_to_object.kshlib b/tests/zfs-tests/tests/functional/block_to_object/block_to_object.kshlib
new file mode 100644
index 000000000000..9de88c9c7d3e
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/block_to_object.kshlib
@@ -0,0 +1,71 @@
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/include/object_store.shlib
+. $STF_SUITE/tests/functional/removal/removal.kshlib
+
+DATASET=$TESTPOOL/$TESTFS
+TESTFILE0=/$DATASET/00
+TESTFILE1=/$DATASET/01
+
+DISK="$(echo $DISKS | cut -d' ' -f1)"
+EXTRADISK="$(echo $DISKS | cut -d' ' -f2)"
+
+function setup_testpool
+{
+	log_must zpool create -f $TESTPOOL $DISK
+
+	log_must zfs create -o compression=lz4 -o recordsize=8k $DATASET
+
+	#
+	# First file is created with writes so initial block-based
+	# pool has some data.
+	#
+	log_must mkfile -n 16M $TESTFILE0
+	log_must randwritecomp $TESTFILE0 4096
+
+	#
+	# Second file is created so it can be used for writes specific
+	# to each test.
+	#
+	log_must mkfile -n 16M $TESTFILE1
+}
+
+function cleanup_testpool
+{
+
+	#
+	# Some tests may start randwritecomp workloads
+	# in the background. Make sure you kill those
+	# instances.
+	#
+	pkill randwritecomp
+
+	if poolexists $TESTPOOL; then
+		log_must zpool sync $TESTPOOL
+		log_must zpool destroy $TESTPOOL
+	fi
+
+	#
+	# We always clear the labels of all disks
+	# between tests so imports from zpool or
+	# or zdb do not get confused with leftover
+	# data from old pools.
+	#
+	for disk in $DISKS; do
+		zpool labelclear -f $disk
+	done
+}
diff --git a/tests/zfs-tests/tests/functional/block_to_object/hybrid_pool_import_export.ksh b/tests/zfs-tests/tests/functional/block_to_object/hybrid_pool_import_export.ksh
new file mode 100755
index 000000000000..44784b3f83c0
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/hybrid_pool_import_export.ksh
@@ -0,0 +1,84 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Ensure that we can add an object store vdev to an existing
+#	block-based pool and that we can import and export it. Once
+#	the object-store vdev is added, we shouldn't be able to import
+#	the pool without the object-store vdev.
+#
+# STRATEGY:
+#	1. Create block-based pool and populate it with some data.
+#	2. Add object-store endpoint/vdev
+#	3. Write some new data
+#	4. Export the pool
+#	5. Attempt to import the pool by only specifying the block
+#	   device (this should fail).
+#	6. Import the pool normally.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+#
+# Add object store
+#
+log_must zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+        -o object-region=$ZTS_REGION \
+        $TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Write some data
+#
+log_must randwritecomp $TESTFILE1 4096
+
+#
+# Get pool guid
+#
+typeset GUID=$(zpool get -Hp -o value guid)
+
+#
+# Export pool
+#
+log_must zpool export $TESTPOOL
+
+#
+# Attempt to import by only specifying the block vdev
+#
+log_mustnot zpool import -d ${DEVICE_DIR:-/dev} $TESTPOOL
+log_mustnot zpool import -d ${DEVICE_DIR:-/dev} $GUID
+
+#
+# Import pool using object-store parameters
+#
+log_must zpool import \
+	-o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	-d $ZTS_BUCKET_NAME \
+	-d ${DEVICE_DIR:-/dev} \
+	$GUID
+
+log_pass "Successfully add object store vdev and write to it."
diff --git a/tests/zfs-tests/tests/functional/block_to_object/zpool_add.ksh b/tests/zfs-tests/tests/functional/block_to_object/zpool_add.ksh
new file mode 100755
index 000000000000..a4ea94f4b9f4
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/zpool_add.ksh
@@ -0,0 +1,90 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Ensure that we can add an object store vdev to an existing
+#	block-based pool and do some writes on it without any
+#	problems.
+#
+# STRATEGY:
+#	1. Create block-based pool and populate it with some data.
+#	2. Add object-store endpoint/vdev
+#	3. Write some new data
+#	4. Read data from both block-based devices and object-store.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+#
+# Add object store
+#
+log_must zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+        -o object-region=$ZTS_REGION \
+        $TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Record allocated space in object store and the normal
+# disk before writes
+#
+log_must zpool sync $TESTPOOL
+OBJ_START=$(zpool list -Hp -o name,alloc -v |  \
+	grep "$ZTS_BUCKET_NAME" | awk '{print $3}')
+DISK_START=$(zpool list -Hp -o name,alloc -v |  \
+	grep "$DISK" | awk '{print $3}')
+
+
+#
+# Write some data that should end up in the object store
+#
+log_must randwritecomp $TESTFILE1 4096
+
+#
+# Record allocated space in object store and the normal
+# disk after writes
+#
+log_must zpool sync $TESTPOOL
+OBJ_END=$(zpool list -Hp -o name,alloc -v |  \
+	grep "$ZTS_BUCKET_NAME" | awk '{print $3}')
+DISK_END=$(zpool list -Hp -o name,alloc -v |  \
+	grep "$DISK" | awk '{print $3}')
+
+#
+# There should be some allocations in the object store by now.
+#
+log_must [ $OBJ_START -lt $OBJ_END ]
+
+#
+# There should be no new allocations in the normal disk.
+#
+log_must [ $DISK_START -ge $DISK_END ]
+
+#
+# Display information for manual checking
+#
+log_must zpool list -v $TESTPOOL
+
+log_pass "Successfully add object store vdev and write to it."
diff --git a/tests/zfs-tests/tests/functional/block_to_object/zpool_add_args_neg.ksh b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_args_neg.ksh
new file mode 100755
index 000000000000..8c00e34401be
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_args_neg.ksh
@@ -0,0 +1,104 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Test invalid arguments passed to zpool-add when adding an
+#	object store vdev.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+#
+# Attempt to add object store without -f option
+#
+log_mustnot zpool add -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt to add object store without bucket name
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE
+
+#
+# Attempt to add object store without endpoint property
+#
+log_mustnot zpool add -f \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt to add object store without region property
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt without both endpoint and region properties
+#
+log_mustnot zpool add -f \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt to add other vdevs together with object store
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $EXTRADISK $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt to add two object stores at the same time
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME \
+	$ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt with bogus bucket name
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE thisisbogus
+
+#
+# Attempt with bogus region
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=thisisbogus \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Attempt with bogus endpoint
+#
+log_mustnot zpool add -f -o object-endpoint=thisisbogus \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+log_pass "Fail as expected when adding object store with invalid args."
diff --git a/tests/zfs-tests/tests/functional/block_to_object/zpool_add_ckpoint.ksh b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_ckpoint.ksh
new file mode 100755
index 000000000000..750438470cf1
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_ckpoint.ksh
@@ -0,0 +1,41 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Ensure that we can't add an object store while the pool has
+#	a checkpoint.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+log_must zpool checkpoint $TESTPOOL
+
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+log_pass "Cannot add object store when checkpointed."
diff --git a/tests/zfs-tests/tests/functional/block_to_object/zpool_add_existing.ksh b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_existing.ksh
new file mode 100755
index 000000000000..4febe9f489e5
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_existing.ksh
@@ -0,0 +1,50 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Ensure we can't add a second object store once the first one
+#	has been added.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+#
+# Add first object store
+#
+log_must zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Fail trying to add a second one
+#
+log_mustnot zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+	-o object-region=$ZTS_REGION \
+	$TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+
+log_pass "Adding a second object store fails."
diff --git a/tests/zfs-tests/tests/functional/block_to_object/zpool_add_with_writes.ksh b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_with_writes.ksh
new file mode 100755
index 000000000000..81f6193800bc
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/block_to_object/zpool_add_with_writes.ksh
@@ -0,0 +1,61 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2023 by Delphix. All rights reserved.
+#
+
+. $STF_SUITE/tests/functional/block_to_object/block_to_object.kshlib
+
+#
+# DESCRIPTION:
+#	Ensure that we can add an object store vdev to an existing
+#	block-based pool while writes are taking place without
+#	any problem.
+#
+# STRATEGY:
+#	1. Create block-based pool and populate it with some data.
+#	2. Start writing data to a file in the pool
+#	3. Add object-store endpoint/vdev while writes are happening.
+#	4. Stop writes when object-store has been added.
+#
+
+verify_runnable "global"
+
+if ! use_object_store; then
+    log_unsupported "Need object store info to migrate block-based pool."
+fi
+
+setup_testpool
+log_onexit cleanup_testpool
+
+#
+# Start writing data in the background
+#
+randwritecomp $TESTFILE1 &
+randwritecomp $TESTFILE1 &
+
+#
+# Add object store
+#
+log_must zpool add -f -o object-endpoint=$ZTS_OBJECT_ENDPOINT \
+        -o object-region=$ZTS_REGION \
+        $TESTPOOL $ZTS_OBJECT_STORE $ZTS_BUCKET_NAME
+
+#
+# Sync writes and kill any writers
+#
+log_must zpool sync $TESTPOOL
+log_must pkill randwritecomp
+
+log_pass "Successfully add object store vdev and write to it."