diff --git a/README.rst b/README.rst
index 0bf30fd..37890da 100644
--- a/README.rst
+++ b/README.rst
@@ -33,7 +33,8 @@ be set automatically if not provided as keyword arguments.
     from stix2 import Indicator
 
     indicator = Indicator(name="File hash for malware variant",
-                          labels=["malicious-activity"],
+                          indicator_types=["malicious-activity"],
+                          pattern_type="stix",
                           pattern="[file:hashes.md5 = 'd41d8cd98f00b204e9800998ecf8427e']")
 
 To parse a STIX JSON string into a Python STIX object, use ``parse()``:
diff --git a/stix2/__init__.py b/stix2/__init__.py
index 26eed6f..10384b1 100644
--- a/stix2/__init__.py
+++ b/stix2/__init__.py
@@ -20,7 +20,7 @@
 
 # flake8: noqa
 
-DEFAULT_VERSION = '2.0'  # Default version will always be the latest STIX 2.X version
+DEFAULT_VERSION = '2.1'  # Default version will always be the latest STIX 2.X version
 
 from .confidence import scales
 from .datastore import CompositeDataSource
@@ -53,7 +53,7 @@ from .patterns import (
     RepeatQualifier, StartStopQualifier, StringConstant, TimestampConstant,
     WithinQualifier,
 )
-from .v20 import *  # This import will always be the latest STIX 2.X version
+from .v21 import *  # This import will always be the latest STIX 2.X version
 from .version import __version__
 from .versioning import new_version, revoke
 
diff --git a/stix2/properties.py b/stix2/properties.py
index 8bb0636..9da5c29 100644
--- a/stix2/properties.py
+++ b/stix2/properties.py
@@ -14,7 +14,7 @@ import stix2
 from .base import _STIXBase
 from .exceptions import (
     CustomContentError, DictionaryKeyError, MissingPropertiesError,
-    MutuallyExclusivePropertiesError,
+    MutuallyExclusivePropertiesError, STIXError,
 )
 from .parsing import STIX2_OBJ_MAPS, parse, parse_observable
 from .utils import _get_dict, get_class_hierarchy_names, parse_into_datetime
@@ -168,6 +168,11 @@ class Property(object):
 
     def __init__(self, required=False, fixed=None, default=None):
         self.required = required
+
+        if required and default:
+            raise STIXError("Cant't use 'required' and 'default' together. 'required'"
+                            "really means 'the user must provide this.'")
+
         if fixed:
             self._fixed_value = fixed
             self.clean = self._default_clean
diff --git a/stix2/test/v21/test_indicator.py b/stix2/test/v21/test_indicator.py
index 76fe86b..8452f70 100644
--- a/stix2/test/v21/test_indicator.py
+++ b/stix2/test/v21/test_indicator.py
@@ -98,8 +98,8 @@ def test_indicator_required_properties():
         stix2.v21.Indicator()
 
     assert excinfo.value.cls == stix2.v21.Indicator
-    assert excinfo.value.properties == ["pattern", "pattern_type", "valid_from"]
-    assert str(excinfo.value) == "No values for required properties for Indicator: (pattern, pattern_type, valid_from)."
+    assert excinfo.value.properties == ["pattern", "pattern_type"]
+    assert str(excinfo.value) == "No values for required properties for Indicator: (pattern, pattern_type)."
 
 
 def test_indicator_required_property_pattern():
@@ -107,7 +107,7 @@ def test_indicator_required_property_pattern():
         stix2.v21.Indicator(indicator_types=['malicious-activity'])
 
     assert excinfo.value.cls == stix2.v21.Indicator
-    assert excinfo.value.properties == ["pattern", "pattern_type", "valid_from"]
+    assert excinfo.value.properties == ["pattern", "pattern_type"]
 
 
 def test_indicator_created_ref_invalid_format():
diff --git a/stix2/v21/sdo.py b/stix2/v21/sdo.py
index 6961423..9418c40 100644
--- a/stix2/v21/sdo.py
+++ b/stix2/v21/sdo.py
@@ -187,7 +187,7 @@ class Indicator(_DomainObject):
         ('pattern', PatternProperty(required=True)),
         ('pattern_type', StringProperty(required=True)),
         ('pattern_version', StringProperty()),
-        ('valid_from', TimestampProperty(default=lambda: NOW, required=True)),
+        ('valid_from', TimestampProperty(default=lambda: NOW)),
         ('valid_until', TimestampProperty()),
         ('kill_chain_phases', ListProperty(KillChainPhase)),
         ('revoked', BooleanProperty(default=lambda: False)),