diff --git a/backuplsststack.sh b/backuplsststack.sh
index 3695342..4756dcc 100755
--- a/backuplsststack.sh
+++ b/backuplsststack.sh
@@ -33,7 +33,10 @@ cd "$ROOT_DIR" || fail "Can't find ${ROOT_DIR}"
 [[ -d "$LSSTSW_DIR/stack" ]] || fail "Can't find stack dir"
 [[ -d "$LSSTSW_DIR/build" ]] || fail "Can't find build dir"
 
-tar --zstd -cf "${TARGET}" lsstsw
+# lsstDoxygen is not an EUPS product -- create_xlinkdocs.sh clones the doc repo
+# and generates HTML under lsstsw/build/, which bloats the tarball and shows up
+# as a package to consumers that enumerate lsstsw/build/*.
+tar --zstd -cf "${TARGET}" --exclude=lsstsw/build/lsstDoxygen lsstsw
 
 gcloud storage cp "${TARGET}" "${GCP_BUCKET}"
 
diff --git a/promotelsststack.sh b/promotelsststack.sh
new file mode 100755
index 0000000..78ffee7
--- /dev/null
+++ b/promotelsststack.sh
@@ -0,0 +1,38 @@
+#!/bin/bash
+
+set -xeo pipefail
+
+# Renames an lsstsw cache tarball in GCP_BUCKET from one tag to another. Used by
+# the release pipelines: run-rebuild uploads the cache under a temporary
+# per-build tag and this promotes it to the shared tag (eg. d_latest) once the
+# release has succeeded. The move is server side, so the multi-GB tarball is
+# never transferred. Every architecture variant present under the source tag is
+# promoted.
+
+GCP_BUCKET="gs://eups-lsstsw-cache"
+
+fail() {
+  echo "$1" >&2
+  exit 1
+}
+
+[[ $# -eq 2 ]] || fail "usage: $0 <src_tag> <dst_tag>"
+SRC_TAG=$1
+DST_TAG=$2
+
+[[ -n "$SRC_TAG" ]] || fail "src tag is empty"
+[[ -n "$DST_TAG" ]] || fail "dst tag is empty"
+
+[[ "$SRC_TAG" != "$DST_TAG" ]] || fail "src and dst tags are identical: ${SRC_TAG}"
+
+# `ls` exits non-zero when nothing matches; report that as our own error rather
+# than dying inside the command substitution.
+objects=$(gcloud storage ls "${GCP_BUCKET}/${SRC_TAG}_*_lsstsw.tar.zst" || true)
+[[ -n "$objects" ]] || fail "no cache tarball found for tag ${SRC_TAG}"
+
+echo "$objects" | while read -r src; do
+  arch=$(basename "$src")
+  arch=${arch#"${SRC_TAG}_"}
+  arch=${arch%_lsstsw.tar.zst}
+  gcloud storage mv "$src" "${GCP_BUCKET}/${DST_TAG}_${arch}_lsstsw.tar.zst"
+done