diff --git a/changes/1448.outlier_detection.1.rst b/changes/1448.outlier_detection.1.rst
new file mode 100644
index 000000000..2080601d1
--- /dev/null
+++ b/changes/1448.outlier_detection.1.rst
@@ -0,0 +1 @@
+Group by obs_id
diff --git a/changes/1448.resample.2.rst b/changes/1448.resample.2.rst
new file mode 100644
index 000000000..2080601d1
--- /dev/null
+++ b/changes/1448.resample.2.rst
@@ -0,0 +1 @@
+Group by obs_id
diff --git a/changes/1448.tweakreg.0.rst b/changes/1448.tweakreg.0.rst
new file mode 100644
index 000000000..2080601d1
--- /dev/null
+++ b/changes/1448.tweakreg.0.rst
@@ -0,0 +1 @@
+Group by obs_id
diff --git a/romancal/datamodels/library.py b/romancal/datamodels/library.py
index 7ca65551a..fa72195d7 100644
--- a/romancal/datamodels/library.py
+++ b/romancal/datamodels/library.py
@@ -75,8 +75,4 @@ def _mapping_to_group_id(mapping):
     """
     Combine a number of file metadata values into a ``group_id`` string
     """
-    return (
-        "roman{program}{observation}{visit}"
-        "_{visit_file_group}{visit_file_sequence}{visit_file_activity}"
-        "_{exposure}"
-    ).format_map(mapping)
+    return "{obs_id}".format_map(mapping)
diff --git a/romancal/outlier_detection/tests/test_outlier_detection.py b/romancal/outlier_detection/tests/test_outlier_detection.py
index 4f8ecf68a..ac9fbbb33 100644
--- a/romancal/outlier_detection/tests/test_outlier_detection.py
+++ b/romancal/outlier_detection/tests/test_outlier_detection.py
@@ -142,7 +142,7 @@ def test_find_outliers(tmp_path, base_image, on_disk):
         img.data[42, 72] = source_value
         img.err[:] = err_value
         img.meta.filename = str(tmp_path / f"img{i}_suffix.asdf")
-        img.meta.observation.exposure = i
+        img.meta.observation.obs_id = str(i)
         img.meta.background.level = 0
         imgs.append(img)
 
diff --git a/romancal/resample/tests/test_resample.py b/romancal/resample/tests/test_resample.py
index b20579f08..93d550485 100644
--- a/romancal/resample/tests/test_resample.py
+++ b/romancal/resample/tests/test_resample.py
@@ -253,6 +253,7 @@ def exposure_1(wfi_sca1, wfi_sca2, wfi_sca3):
             "2020-02-01T00:02:30", format="isot", scale="utc"
         )
         sca.meta.observation["exposure"] = 1
+        sca.meta.observation["obs_id"] = "1"
     return [wfi_sca1, wfi_sca2, wfi_sca3]
 
 
@@ -268,6 +269,7 @@ def exposure_2(wfi_sca4, wfi_sca5, wfi_sca6):
             "2020-05-01T00:02:30", format="isot", scale="utc"
         )
         sca.meta.observation["exposure"] = 2
+        sca.meta.observation["obs_id"] = "2"
     return [wfi_sca4, wfi_sca5, wfi_sca6]
 
 
diff --git a/romancal/tweakreg/tests/test_tweakreg.py b/romancal/tweakreg/tests/test_tweakreg.py
index 63dad8e5a..b8434bccc 100644
--- a/romancal/tweakreg/tests/test_tweakreg.py
+++ b/romancal/tweakreg/tests/test_tweakreg.py
@@ -908,7 +908,9 @@ def test_tweakreg_handles_multiple_groups(tmp_path, base_image):
     add_tweakreg_catalog_attribute(tmp_path, img2, catalog_filename="img2")
 
     img1.meta.observation["program"] = "-program_id1"
+    img1.meta.observation["obs_id"] = "1"
     img2.meta.observation["program"] = "-program_id2"
+    img2.meta.observation["obs_id"] = "2"
 
     img1.meta["filename"] = "file1.asdf"
     img2.meta["filename"] = "file2.asdf"
@@ -918,10 +920,7 @@ def test_tweakreg_handles_multiple_groups(tmp_path, base_image):
     assert len(res.group_names) == 2
     with res:
         for r, i in zip(res, [img1, img2]):
-            assert (
-                r.meta.group_id.split("-")[1]
-                == i.meta.observation.program.split("-")[1]
-            )
+            assert r.meta.group_id == i.meta.observation.obs_id
             res.shelve(r, modify=False)