From 0bc5384b8090bd9ca2646a84803269bafd2d211a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Feb 2026 00:35:59 +0000
Subject: [PATCH 1/4] Initial plan


From 6ec27c20a41e80a01beac4a488b6cc422c48a09c Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Feb 2026 00:40:29 +0000
Subject: [PATCH 2/4] Use UTC (Z) for timestamps to avoid ambiguity

Co-authored-by: keighrim <9062727+keighrim@users.noreply.github.com>
---
 VERSION                 | 1 +
 mmif/serialize/mmif.py  | 4 ++--
 mmif/serialize/model.py | 4 +++-
 3 files changed, 6 insertions(+), 3 deletions(-)
 create mode 100644 VERSION

diff --git a/VERSION b/VERSION
new file mode 100644
index 00000000..4feaf3b9
--- /dev/null
+++ b/VERSION
@@ -0,0 +1 @@
+1.0.0.dev1
diff --git a/mmif/serialize/mmif.py b/mmif/serialize/mmif.py
index 68478c7f..245c96aa 100644
--- a/mmif/serialize/mmif.py
+++ b/mmif/serialize/mmif.py
@@ -14,7 +14,7 @@
 import math
 import warnings
 from collections import defaultdict
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any, List, Union, Optional, Dict, cast, Iterator
 
 import jsonschema.validators
@@ -433,7 +433,7 @@ def new_view(self) -> View:
         """
         new_view = View()
         new_view.id = self.new_view_id()
-        new_view.metadata.timestamp = datetime.now()
+        new_view.metadata.timestamp = datetime.now(timezone.utc)
         self.add_view(new_view)
         return new_view
 
diff --git a/mmif/serialize/model.py b/mmif/serialize/model.py
index 1bec7b29..6f26b8eb 100644
--- a/mmif/serialize/model.py
+++ b/mmif/serialize/model.py
@@ -402,7 +402,9 @@ def default(self, obj: 'MmifObject'):
         if hasattr(obj, '_serialize'):
             return obj._serialize()
         elif hasattr(obj, 'isoformat'):         # for datetime objects
-            return obj.isoformat()
+            iso_str = obj.isoformat()
+            # Use 'Z' suffix for UTC timestamps instead of '+00:00'
+            return iso_str.replace('+00:00', 'Z')
         elif hasattr(obj, '__str__'):
             return str(obj)
         else:

From 9881e4014f5f283c90c953afbbb909423abd40a2 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Feb 2026 00:43:29 +0000
Subject: [PATCH 3/4] Add test for UTC timestamp with Z suffix

Co-authored-by: keighrim <9062727+keighrim@users.noreply.github.com>
---
 VERSION                 |  1 -
 tests/test_serialize.py | 27 +++++++++++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)
 delete mode 100644 VERSION

diff --git a/VERSION b/VERSION
deleted file mode 100644
index 4feaf3b9..00000000
--- a/VERSION
+++ /dev/null
@@ -1 +0,0 @@
-1.0.0.dev1
diff --git a/tests/test_serialize.py b/tests/test_serialize.py
index 9e857a00..11b06d87 100644
--- a/tests/test_serialize.py
+++ b/tests/test_serialize.py
@@ -608,6 +608,33 @@ def test_get_label(self):
             a = v.new_annotation(AnnotationTypes.BoundingBox)
             _ = a._get_label()
 
+    def test_timestamp_uses_utc_with_z_suffix(self):
+        """Test that timestamps are in UTC with 'Z' suffix to avoid ambiguity"""
+        from datetime import timezone
+        mmif_str = '''
+        {
+          "metadata": {"mmif": "http://mmif.clams.ai/1.0.0"},
+          "documents": [],
+          "views": []
+        }'''
+        mmif_obj = Mmif(mmif_str)
+        
+        # Create a new view using new_view() - should set UTC timestamp
+        new_view = mmif_obj.new_view()
+        new_view.metadata.app = "http://test.app"
+        
+        # Verify the timestamp is timezone-aware and uses UTC
+        self.assertIsNotNone(new_view.metadata.timestamp)
+        self.assertIsNotNone(new_view.metadata.timestamp.tzinfo)
+        self.assertEqual(new_view.metadata.timestamp.tzinfo, timezone.utc)
+        
+        # Verify serialization uses 'Z' suffix instead of '+00:00'
+        serialized = mmif_obj.serialize()
+        self.assertIn('"timestamp":', serialized)
+        # The timestamp should end with Z (not +00:00)
+        self.assertIn('Z"', serialized)
+        self.assertNotIn('+00:00', serialized)
+
     def test_get_anchor_point(self):
         mmif = Mmif(validate=False)
         v1 = mmif.new_view()

From b1eca88a512b7c274d54e1b9f7a93b62ff06a282 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Feb 2026 00:45:23 +0000
Subject: [PATCH 4/4] Improve encoder to only use Z for explicit UTC timezone

Co-authored-by: keighrim <9062727+keighrim@users.noreply.github.com>
---
 mmif/serialize/model.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mmif/serialize/model.py b/mmif/serialize/model.py
index 6f26b8eb..f7c56b3f 100644
--- a/mmif/serialize/model.py
+++ b/mmif/serialize/model.py
@@ -23,7 +23,7 @@
 
 import json
 import warnings
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Union, Any, Dict, Optional, TypeVar, Generic, Generator, Iterator, Type, Set, ClassVar, List
 
 T = TypeVar('T')
@@ -404,7 +404,10 @@ def default(self, obj: 'MmifObject'):
         elif hasattr(obj, 'isoformat'):         # for datetime objects
             iso_str = obj.isoformat()
             # Use 'Z' suffix for UTC timestamps instead of '+00:00'
-            return iso_str.replace('+00:00', 'Z')
+            # Only replace if the datetime is explicitly in UTC timezone
+            if hasattr(obj, 'tzinfo') and obj.tzinfo == timezone.utc:
+                return iso_str.replace('+00:00', 'Z')
+            return iso_str
         elif hasattr(obj, '__str__'):
             return str(obj)
         else: