diff --git a/.ci/gh_buildkit_cache_usage.sh b/.ci/gh_buildkit_cache_usage.sh
index 728fa87af..4904d9d35 100755
--- a/.ci/gh_buildkit_cache_usage.sh
+++ b/.ci/gh_buildkit_cache_usage.sh
@@ -1,19 +1,19 @@
 #!/bin/bash
-# Reports total count and size of GitHub Actions caches whose key starts with a given prefix.
-# Used for BuildKit GHA cache (keys like buildkit-blob-1-sha256:...).
+# Reports GitHub Actions cache usage: either grouped by key prefix or for a single prefix.
+# Prefix = first segment of key (before first "-" or "/"). E.g. buildkit-blob-* -> buildkit, vcpkg/xxx -> vcpkg.
 #
 # Requires: gh (GitHub CLI), jq
 # Run from repo root with gh auth login already done (or GITHUB_TOKEN set in CI).
 #
 # Usage: .ci/gh_buildkit_cache_usage.sh [key-prefix]
-#   Default key-prefix: buildkit-blob
+#   No args: fetch all caches, group by prefix, print table (count + size per prefix) and grand total.
+#   One arg: report only caches whose key starts with key-prefix (default: buildkit-blob).
 #
-# Example: .ci/gh_buildkit_cache_usage.sh
-# Example: .ci/gh_buildkit_cache_usage.sh buildkit-blob
+# Example: .ci/gh_buildkit_cache_usage.sh              # all prefixes
+# Example: .ci/gh_buildkit_cache_usage.sh buildkit-blob # single prefix
 
 set -eo pipefail
 
-KEY_PREFIX="${1:-buildkit-blob}"
 LIMIT=1000
 
 if ! command -v gh &>/dev/null; then
@@ -25,6 +25,35 @@ if ! command -v jq &>/dev/null; then
   exit 1
 fi
 
+if [[ $# -eq 0 ]]; then
+  # Grouped mode: all caches, group by first segment (before - or /)
+  json=$(gh cache list --limit "$LIMIT" --json key,sizeInBytes 2>/dev/null) || {
+    echo "Error: gh cache list failed (check gh auth or repo access)" >&2
+    exit 1
+  }
+  # Add prefix field, group by prefix, sum count and size, sort by size desc; output GiB (2 decimals)
+  total_entries=$(echo "$json" | jq 'length')
+  total_bytes=$(echo "$json" | jq 'map(.sizeInBytes) | add // 0')
+  total_gib=$(echo "$total_bytes" | jq -r '. / 1024 / 1024 / 1024 | . * 100 | floor / 100')
+  printf "%-12s %6s %10s\n" "PREFIX" "COUNT" "SIZE (GiB)"
+  printf "%-12s %6s %10s\n" "------------" "------" "----------"
+  while IFS=$'\t' read -r prefix count gib; do
+    printf "%-12s %6s %10.2f\n" "$prefix" "$count" "$gib"
+  done < <(echo "$json" | jq -r '
+    def prefix: (if (.key | test("/")) then (.key | split("/")[0]) else (.key | split("-")[0]) end);
+    def to_gib: . / 1024 / 1024 / 1024 | . * 100 | floor / 100;
+    map(. + {prefix: prefix}) | group_by(.prefix) |
+    map({prefix: .[0].prefix, count: length, totalBytes: (map(.sizeInBytes) | add // 0)}) |
+    sort_by(-.totalBytes) |
+    .[] | "\(.prefix)\t\(.count)\t\(.totalBytes | to_gib)"
+  ')
+  echo ""
+  printf "Total: %s entries, %s GiB\n" "$total_entries" "$total_gib"
+  exit 0
+fi
+
+# Single-prefix mode
+KEY_PREFIX="${1:-buildkit-blob}"
 json=$(gh cache list --key "$KEY_PREFIX" --limit "$LIMIT" --json key,sizeInBytes 2>/dev/null) || {
   echo "Error: gh cache list failed (check gh auth or repo access)" >&2
   exit 1
@@ -32,8 +61,6 @@ json=$(gh cache list --key "$KEY_PREFIX" --limit "$LIMIT" --json key,sizeInBytes
 
 count=$(echo "$json" | jq 'length')
 total_bytes=$(echo "$json" | jq 'map(.sizeInBytes) | add // 0')
-
-# Human-readable size (GiB, 2 decimals)
 total_gib=$(echo "$total_bytes" | jq -r '. / 1024 / 1024 / 1024 | . * 100 | floor / 100')
 
 echo "Cache key prefix: $KEY_PREFIX"