diff --git a/hermes_cli/backup.py b/hermes_cli/backup.py
index 9c4d4fe4dad25..fda440d66efa2 100644
--- a/hermes_cli/backup.py
+++ b/hermes_cli/backup.py
@@ -563,11 +563,14 @@ def _print_capped(header: str, lines: List[str], indent: str) -> None:
 
 # --- Backup ---
 
+_RUN_BACKUP_PREFIX = "hermes-backup-"
+
+
 def _resolve_backup_output_path(output: Optional[str]) -> Path:
     """Turn ``--output`` (file, directory, or None) into a ``.zip`` path whose parent exists;
     an unwritable path exits with a one-line error, not a traceback."""
     out_path = None
-    default_name = f"hermes-backup-{datetime.now().strftime('%Y-%m-%d-%H%M%S')}.zip"
+    default_name = f"{_RUN_BACKUP_PREFIX}{datetime.now().strftime('%Y-%m-%d-%H%M%S')}.zip"
     try:
         if output:
             out_path = Path(output).expanduser().resolve()
@@ -679,6 +682,11 @@ def _progress(i: int) -> None:
         _print_capped(f"\n  Warnings ({len(errors)} files skipped):", errors, "  ")
     else:
         print(f"\nRestore with: hermes import {out_path.name}")
+    keep = getattr(args, "keep", 0)  # 0 / absent: never prune (non-CLI callers)
+    if keep and out_path.name.startswith(_RUN_BACKUP_PREFIX):
+        pruned = _prune_prefixed_zips(out_path.parent, _RUN_BACKUP_PREFIX, keep, "backup")
+        if pruned:
+            print(f"  Pruned {pruned} older {_RUN_BACKUP_PREFIX}*.zip (keeping {keep}).")
 
 
 # --- Import ---
diff --git a/hermes_cli/subcommands/backup.py b/hermes_cli/subcommands/backup.py
index 5ec7ac27214c2..282b3773f8dbf 100644
--- a/hermes_cli/subcommands/backup.py
+++ b/hermes_cli/subcommands/backup.py
@@ -20,4 +20,8 @@ def build_backup_parser(subparsers, *, cmd_backup: Callable) -> None:
         help="Quick snapshot: only critical state files (config, state.db, .env, auth, cron)")
     backup_parser.add_argument(
         "-l", "--label", help="Label for the snapshot (only used with --quick)")
+    backup_parser.add_argument(
+        "-k", "--keep", type=int, default=3, metavar="N",
+        help="After a full backup, delete older hermes-backup-*.zip files in the output "
+             "directory beyond the newest N (default 3; 0 keeps everything)")
     backup_parser.set_defaults(func=cmd_backup)
diff --git a/tests/hermes_cli/test_backup.py b/tests/hermes_cli/test_backup.py
index 58b49c842a214..abc5bf6dcb680 100644
--- a/tests/hermes_cli/test_backup.py
+++ b/tests/hermes_cli/test_backup.py
@@ -2423,3 +2423,25 @@ def _count_rows(db_path: Path) -> tuple[int, int]:
         )
     finally:
         conn.close()
+
+
+def test_run_backup_prunes_older_default_named_zips_but_not_others(tmp_path, monkeypatch):
+    """Hourly `hermes backup` callers accumulated 150+ zips; --keep bounds the default-named
+    ones and leaves custom-named or foreign zips alone (#81317)."""
+    from argparse import Namespace
+    from hermes_cli import backup as backup_mod
+
+    home = tmp_path / ".hermes"
+    home.mkdir()
+    (home / "config.yaml").write_text("model: x\n")
+    monkeypatch.setenv("HERMES_HOME", str(home))
+    monkeypatch.setattr(Path, "home", lambda: tmp_path)
+    for i in range(4):
+        (tmp_path / f"hermes-backup-2026-01-0{i + 1}-000000.zip").write_bytes(b"old")
+    (tmp_path / "my-archive.zip").write_bytes(b"mine")
+
+    backup_mod.run_backup(Namespace(output=None, keep=2))
+
+    kept = sorted(p.name for p in tmp_path.glob("hermes-backup-*.zip"))
+    assert len(kept) == 2 and kept[0] == "hermes-backup-2026-01-04-000000.zip"
+    assert (tmp_path / "my-archive.zip").exists()
diff --git a/website/docs/reference/cli-commands.md b/website/docs/reference/cli-commands.md
index b5e6093e6e548..d5a4bf320a17f 100644
--- a/website/docs/reference/cli-commands.md
+++ b/website/docs/reference/cli-commands.md
@@ -950,6 +950,7 @@ Create a zip archive of your Hermes configuration, skills, sessions, and data. T
 | `-o`, `--output <path>` | Output path for the zip file (default: `~/hermes-backup-<timestamp>.zip`). |
 | `-q`, `--quick` | Quick snapshot: only critical state files (config.yaml, state.db, .env, auth, cron jobs). Much faster than a full backup. |
 | `-l`, `--label <name>` | Label for the snapshot (only used with `--quick`). |
+| `-k`, `--keep <N>` | After a full backup, delete older `hermes-backup-*.zip` files in the output directory beyond the newest N (default 3; `0` keeps everything). Custom-named zips are never touched. |
 
 The backup uses SQLite's `backup()` API for safe copying, so it works correctly even when Hermes is running (WAL-mode safe).