diff --git a/storage_controller/src/main.rs b/storage_controller/src/main.rs
index 1a7f9a2366..8c834f9acb 100644
--- a/storage_controller/src/main.rs
+++ b/storage_controller/src/main.rs
@@ -115,19 +115,17 @@ struct Cli {
     #[arg(long)]
     split_threshold: Option<u64>,
 
-    /// Maximum number of shards during autosplits. 0 disables autosplits.
-    // TODO: defaults to 8 for backwards compatibility, should default to 255.
-    #[arg(long, default_value = "8")]
+    /// Maximum number of shards during autosplits. 0 disables autosplits. Defaults
+    /// to 16 as a safety to avoid too many shards by accident.
+    #[arg(long, default_value = "16")]
     max_split_shards: u8,
 
     /// Size threshold for initial shard splits of unsharded tenants. 0 disables initial splits.
-    // TODO: defaults to 64 GB for backwards compatibility. Should default to None.
-    #[arg(long, default_value = "68719476736")]
-    initial_split_threshold: u64,
+    #[arg(long)]
+    initial_split_threshold: Option<u64>,
 
-    /// Number of target shards for initial splits. 0 or 1 disables initial splits.
-    // TODO: defaults to 8 for backwards compatibility. Should default to 2.
-    #[arg(long, default_value = "8")]
+    /// Number of target shards for initial splits. 0 or 1 disables initial splits. Defaults to 2.
+    #[arg(long, default_value = "2")]
     initial_split_shards: u8,
 
     /// Maximum number of normal-priority reconcilers that may run in parallel
@@ -417,7 +415,7 @@ async fn async_main() -> anyhow::Result<()> {
         tenant_rate_limit: args.tenant_rate_limit,
         split_threshold: args.split_threshold,
         max_split_shards: args.max_split_shards,
-        initial_split_threshold: Some(args.initial_split_threshold),
+        initial_split_threshold: args.initial_split_threshold,
         initial_split_shards: args.initial_split_shards,
         neon_local_repo_dir: args.neon_local_repo_dir,
         max_secondary_lag_bytes: args.max_secondary_lag_bytes,