diff --git a/stix2/__init__.py b/stix2/__init__.py
index 68e0264..714bf46 100644
--- a/stix2/__init__.py
+++ b/stix2/__init__.py
@@ -54,7 +54,7 @@ from .patterns import (
     WithinQualifier,
 )
 from .utils import new_version, revoke
-from .v21 import *  # This import will always be the latest STIX 2.X version
+from .v20 import *  # This import will always be the latest STIX 2.X version
 from .version import __version__
 
 _collect_stix2_mappings()
diff --git a/stix2/test/v20/test_bundle.py b/stix2/test/v20/test_bundle.py
index df59f89..f53d0cb 100644
--- a/stix2/test/v20/test_bundle.py
+++ b/stix2/test/v20/test_bundle.py
@@ -176,7 +176,7 @@ def test_parse_bundle(version):
 
     assert bundle.type == "bundle"
     assert bundle.id.startswith("bundle--")
-    assert type(bundle.objects[0]) is stix2.v20.Indicator
+    assert isinstance(bundle.objects[0], stix2.v20.Indicator)
     assert bundle.objects[0].type == 'indicator'
     assert bundle.objects[1].type == 'malware'
     assert bundle.objects[2].type == 'relationship'
diff --git a/stix2/test/v20/test_core.py b/stix2/test/v20/test_core.py
index c2056b8..d2efa22 100644
--- a/stix2/test/v20/test_core.py
+++ b/stix2/test/v20/test_core.py
@@ -74,7 +74,9 @@ def test_register_object_with_version():
     v = 'v20'
 
     assert bundle.objects[0].type in core.STIX2_OBJ_MAPS[v]['objects']
-    assert v in str(bundle.objects[0].__class__)
+    # spec_version is not in STIX 2.0, and is required in 2.1, so this
+    # suffices as a test for a STIX 2.0 object.
+    assert "spec_version" not in bundle.objects[0]
 
 
 def test_register_marking_with_version():
diff --git a/stix2/test/v20/test_custom.py b/stix2/test/v20/test_custom.py
index 8a99b2c..3cfc23f 100644
--- a/stix2/test/v20/test_custom.py
+++ b/stix2/test/v20/test_custom.py
@@ -96,7 +96,7 @@ def test_identity_custom_property_allowed():
 def test_parse_identity_custom_property(data):
     with pytest.raises(stix2.exceptions.ExtraPropertiesError) as excinfo:
         stix2.parse(data, version="2.0")
-    assert excinfo.value.cls == stix2.v20.Identity
+    assert issubclass(excinfo.value.cls, stix2.v20.Identity)
     assert excinfo.value.properties == ['foo']
     assert "Unexpected properties for" in str(excinfo.value)
 
diff --git a/stix2/test/v21/test_workbench.py b/stix2/test/v20/test_workbench.py
similarity index 96%
rename from stix2/test/v21/test_workbench.py
rename to stix2/test/v20/test_workbench.py
index 3a4a3fd..c254966 100644
--- a/stix2/test/v21/test_workbench.py
+++ b/stix2/test/v20/test_workbench.py
@@ -29,7 +29,7 @@ def test_workbench_environment():
     save(ind)
 
     resp = get(INDICATOR_ID)
-    assert resp['indicator_types'][0] == 'malicious-activity'
+    assert resp['labels'][0] == 'malicious-activity'
 
     resp = all_versions(INDICATOR_ID)
     assert len(resp) == 1
@@ -147,7 +147,7 @@ def test_workbench_get_all_vulnerabilities():
 
 def test_workbench_add_to_bundle():
     vuln = Vulnerability(**VULNERABILITY_KWARGS)
-    bundle = stix2.v21.Bundle(vuln)
+    bundle = stix2.v20.Bundle(vuln)
     assert bundle.objects[0].name == 'Heartbleed'
 
 
@@ -186,10 +186,7 @@ def test_workbench_related():
 
 
 def test_workbench_related_with_filters():
-    malware = Malware(
-        malware_types=["ransomware"], name="CryptorBit",
-        created_by_ref=IDENTITY_ID, is_family=False,
-    )
+    malware = Malware(labels=["ransomware"], name="CryptorBit", created_by_ref=IDENTITY_ID)
     rel = Relationship(malware.id, 'variant-of', MALWARE_ID)
     save([malware, rel])
 
@@ -274,12 +271,12 @@ def test_default_object_marking_refs():
 
 
 def test_workbench_custom_property_object_in_observable_extension():
-    ntfs = stix2.v21.NTFSExt(
+    ntfs = stix2.v20.NTFSExt(
         allow_custom=True,
         sid=1,
         x_foo='bar',
     )
-    artifact = stix2.v21.File(
+    artifact = stix2.v20.File(
         name='test',
         extensions={'ntfs-ext': ntfs},
     )
@@ -296,7 +293,7 @@ def test_workbench_custom_property_object_in_observable_extension():
 
 
 def test_workbench_custom_property_dict_in_observable_extension():
-    artifact = stix2.v21.File(
+    artifact = stix2.v20.File(
         allow_custom=True,
         name='test',
         extensions={