diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9e1de3c8..b477cd02 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,7 +6,9 @@ _When adding new entries to the changelog, please include issue/PR numbers where
 
 ## Unreleased
 
+- diff/show: Faster output for some large repositories (varies wildly) [#1038](https://github.com/koordinates/kart/issues/1038)
 - show: Added `--no-sort-keys` option to disable sorting of features by name/PK. Previously added to `diff` only
+- show: Added `--add-feature-count-estimate` option to add a feature count estimate to `json-lines` output. Previously added to `diff` only
 
 ## 0.16.1
 
diff --git a/kart/show.py b/kart/show.py
index 5983bbaa..618d1658 100644
--- a/kart/show.py
+++ b/kart/show.py
@@ -65,6 +65,16 @@
         "Otherwise, the feature count will be approximated with varying levels of accuracy."
     ),
 )
+@click.option(
+    "--add-feature-count-estimate",
+    default=None,
+    type=click.Choice(diff_estimation.ACCURACY_CHOICES),
+    help=(
+        "Adds a feature count estimate to this diff (used with `--output-format json-lines` only.) "
+        "The estimate will be calculated while the diff is being generated, and will be added to "
+        "the stream when it is ready. If the estimate is not ready before the process exits, it will not be added."
+    ),
+)
 @click.option(
     "--diff-files",
     is_flag=True,
@@ -109,6 +119,7 @@ def show(
     output_path,
     exit_code,
     only_feature_count,
+    add_feature_count_estimate,
     diff_files,
     args,
     diff_format=DiffFormat.FULL,
@@ -161,6 +172,7 @@ def show(
         delta_filter=delta_filter,
         target_crs=crs,
         sort_keys=sort_keys,
+        diff_estimate_accuracy=add_feature_count_estimate,
     )
     diff_writer.full_file_diffs(diff_files)
     diff_writer.include_target_commit_as_header()