diff --git a/gc/expunge-releases/expunge-releases.py b/gc/expunge-releases/expunge-releases.py
new file mode 100644
index 0000000..57f5971
--- /dev/null
+++ b/gc/expunge-releases/expunge-releases.py
@@ -0,0 +1,124 @@
+from datetime import datetime
+import os
+import re
+import sys
+
+release_dirs = ["nixos", "nixpkgs"]
+
+name_to_release = re.compile('(nixos|nixpkgs)-(darwin-)?(\d\d.\d\d)')
+version_split = re.compile('-|\.|alpha|beta|pre')
+is_prerelease = re.compile('alpha|beta|pre')
+
+minimum_release_to_keep = "23.05"
+
+def log(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+class FileEntry:
+    def __init__(self, date, size, key):
+        self.date = date
+        self.size = size
+        self.key = key
+
+def parse_file(filename):
+    entries = []
+    with open(filename, 'r') as file:
+        for line in file:
+            #date = datetime.strptime(line[0:19], "%Y-%m-%d %H:%M:%S")
+            date = None # don't need it
+            size = int(line[19:31])
+            key = line[31:].rstrip('\n')
+            entry = FileEntry(date, size, key)
+            entries.append(entry)
+    return entries
+
+class Release:
+    def __init__(self, name, date):
+        self.name = name
+        self.date = date
+        self.files = []
+
+    def major_release(self):
+        basename = os.path.basename(self.name)
+        m = name_to_release.match(basename)
+        return m[3] if m else None
+
+    def sort_key(self):
+        # Prereleases get sorted before non-prereleases.
+        # Pad integer components to compare them numerically.
+        name = os.path.basename(self.name)
+        return [not re.search(is_prerelease, name)] + [maybe_pad_int(s) for s in re.split(version_split, name)]
+
+def maybe_pad_int(s):
+    return s.zfill(10) if s.isdigit() else s
+
+releases = dict()
+
+filename = "bucket-contents"
+file_entries = parse_file(filename)
+
+# Gather all releases. These are identified by having a "src-url" file
+# in them.
+for entry in file_entries:
+    if entry.key.endswith("src-url"):
+        #log("Date:", entry.date, "Size:", entry.size, "Name:", entry.key)
+        name = os.path.dirname(entry.key)
+        releases[name] = Release(name, entry.date)
+
+# Get the files for each release.
+for entry in file_entries:
+    rel_name = os.path.dirname(entry.key)
+    rel = releases.get(rel_name)
+    if rel is not None:
+        rel.files.append(entry)
+
+log("Found {} releases.".format(len(releases)))
+
+# Group the releases by parent directory (like nixpkgs/23.11-darwin/).
+release_parents = dict()
+
+for rel in releases.values():
+    parent_dir = os.path.dirname(rel.name)
+    release_parents.setdefault(parent_dir, []).append(rel)
+
+# For each parent directory, group the releases by major release
+# (e.g. 23.11).
+expunged_releases = 0
+expunged_files = 0
+expunged_size = 0
+
+for release_parent_name, rels in release_parents.items():
+    major_releases = dict()
+    for rel in rels:
+        major_release = rel.major_release()
+        if major_release is None:
+            log("Skipping release '{}'.".format(rel.name))
+        else:
+            major_releases.setdefault(major_release, []).append(rel)
+
+    for major_release_name, rels in major_releases.items():
+        if major_release_name >= minimum_release_to_keep:
+            log("Keeping all {} releases in major release group '{}/{}'.".format(len(rels), release_parent_name, major_release_name))
+        else:
+            # Sort the releases by release name (lexicographically after splitting into version components), keep the newest one.
+            sorted_rels = sorted(rels, key=lambda rel: rel.sort_key())
+            log("Major release group '{}/{}' ({} releases).".format(release_parent_name, major_release_name, len(rels)))
+            #for rel in sorted_rels:
+            #    log("  ", rel.date, rel.name, rel.sort_key())
+
+            # Keep the most recent release in the group.
+            most_recent_rel = sorted_rels.pop()
+
+            # Expunge the other releases.
+            for rel in sorted_rels:
+                rel_size = sum([f.size for f in rel.files])
+                log("  Expunging release '{}' ({} files, {:.2f} MiB).".format(rel.name, len(rel.files), rel_size / 1024**2))
+                for f in rel.files:
+                    print(f.key)
+                expunged_releases += 1
+                expunged_files += len(rel.files)
+                expunged_size += rel_size
+
+            log("  Keeping release '{}'.".format(most_recent_rel.name))
+
+log("Expunged {} releases, {} files, {:.2f} GiB.".format(expunged_releases, expunged_files, expunged_size / 1024**3))