diff --git a/arborist/wallet/bucket.py b/arborist/wallet/bucket.py
index 3dcfca7..fc278be 100644
--- a/arborist/wallet/bucket.py
+++ b/arborist/wallet/bucket.py
@@ -799,26 +799,39 @@ class MultiShardSidecarCorpus:
         cache_bytes_per_shard: int = DEFAULT_CACHE_BYTES,
         sidecar_cache_dir: str | None = None,
     ):
+        from concurrent.futures import ThreadPoolExecutor
+
         self.manifest = manifest
-        self.shard_clients = []
-        self._has_sidecar: list[bool] = []
-        for sh in manifest.shards:
+        self._has_sidecar: list[bool] = [
+            bool(sh.get("sidecar_url")) for sh in manifest.shards
+        ]
+
+        # Pre-download every sidecar in parallel so a fresh consumer
+        # pays max(per-sidecar download) instead of sum. SidecarShardClient
+        # is idempotent — if the cache file already exists, it just reads
+        # from disk (no re-download). Bucket-only shards (no sidecar)
+        # construct fast; they don't pre-pull the .db.
+        def _build(item):
+            i, sh = item
             if sh.get("sidecar_url"):
-                client = SidecarShardClient(
+                return i, SidecarShardClient(
                     shard_url=sh["url"],
                     sidecar_url=sh["sidecar_url"],
                     blob_base=manifest.blob_base,
                     cache_bytes=cache_bytes_per_shard,
                     sidecar_cache_dir=sidecar_cache_dir,
                 )
-                self._has_sidecar.append(True)
-            else:
-                client = BucketClient(
-                    BucketEndpoint(shard_url=sh["url"], blob_base=manifest.blob_base),
-                    cache_bytes=cache_bytes_per_shard,
-                )
-                self._has_sidecar.append(False)
-            self.shard_clients.append(client)
+            return i, BucketClient(
+                BucketEndpoint(shard_url=sh["url"], blob_base=manifest.blob_base),
+                cache_bytes=cache_bytes_per_shard,
+            )
+
+        n = len(manifest.shards)
+        results: list = [None] * n
+        with ThreadPoolExecutor(max_workers=max(1, n)) as ex:
+            for i, client in ex.map(_build, enumerate(manifest.shards)):
+                results[i] = client
+        self.shard_clients = results
         self._by_url = {sh["url"]: c for sh, c in zip(manifest.shards, self.shard_clients)}
 
     def close(self):