diff --git a/crates/chain/src/indexer/keychain_txout.rs b/crates/chain/src/indexer/keychain_txout.rs
index bdea4b82d..bcb4937cd 100644
--- a/crates/chain/src/indexer/keychain_txout.rs
+++ b/crates/chain/src/indexer/keychain_txout.rs
@@ -9,12 +9,14 @@ use crate::{
     spk_txout::SpkTxOutIndex,
     DescriptorExt, DescriptorId, Indexed, Indexer, KeychainIndexed, SpkIterator,
 };
-use alloc::{borrow::ToOwned, vec::Vec};
+use alloc::{borrow::ToOwned, sync::Arc, vec::Vec};
 use bitcoin::{Amount, OutPoint, ScriptBuf, SignedAmount, Transaction, TxOut, Txid};
 use core::{
     fmt::Debug,
     ops::{Bound, RangeBounds},
 };
+#[cfg(feature = "std")]
+use std::thread;
 
 use crate::Merge;
 
@@ -445,6 +447,8 @@ impl<K: Clone + Ord + Debug> KeychainTxOutIndex<K> {
     }
 
     /// Syncs the state of the inner spk index after changes to a keychain
+    /// Note: Uses multithreading to parallelize the derivation of script pubkeys when processing
+    /// more than 1000 indices (only when the std feature is enabled)
     fn replenish_inner_index(&mut self, did: DescriptorId, keychain: &K, lookahead: u32) {
         let descriptor = self.descriptors.get(&did).expect("invariant");
         let next_store_index = self
@@ -454,13 +458,92 @@ impl<K: Clone + Ord + Debug> KeychainTxOutIndex<K> {
             .last()
             .map_or(0, |((_, index), _)| *index + 1);
         let next_reveal_index = self.last_revealed.get(&did).map_or(0, |v| *v + 1);
-        for (new_index, new_spk) in
-            SpkIterator::new_with_range(descriptor, next_store_index..next_reveal_index + lookahead)
+        let end_index = next_reveal_index + lookahead;
+
+        if next_store_index >= end_index {
+            return;
+        }
+
+        let total_indices = end_index - next_store_index;
+
+        // Helper function to generate script pubkeys in a single-threaded manner
+        let generate_spks = |descriptor: &Descriptor<DescriptorPublicKey>,
+                             start: u32,
+                             end: u32|
+         -> Vec<(u32, ScriptBuf)> {
+            let mut results = Vec::with_capacity((end - start) as usize);
+            for (new_index, new_spk) in SpkIterator::new_with_range(descriptor, start..end) {
+                results.push((new_index, new_spk));
+            }
+            results
+        };
+
+        let process_results = |this: &mut Self, results: Vec<(u32, ScriptBuf)>| {
+            for (new_index, new_spk) in results {
+                let _inserted = this
+                    .inner
+                    .insert_spk((keychain.clone(), new_index), new_spk);
+                debug_assert!(_inserted, "replenish lookahead: must not have existing spk: keychain={:?}, lookahead={}, next_store_index={}, next_reveal_index={}", keychain, lookahead, next_store_index, next_reveal_index);
+            }
+        };
+
+        #[cfg(not(feature = "std"))]
         {
-            let _inserted = self
-                .inner
-                .insert_spk((keychain.clone(), new_index), new_spk);
-            debug_assert!(_inserted, "replenish lookahead: must not have existing spk: keychain={:?}, lookahead={}, next_store_index={}, next_reveal_index={}", keychain, lookahead, next_store_index, next_reveal_index);
+            let results = generate_spks(descriptor, next_store_index, end_index);
+            process_results(self, results);
+            return;
+        }
+
+        #[cfg(feature = "std")]
+        {
+            if total_indices < 1000 {
+                let results = generate_spks(descriptor, next_store_index, end_index);
+                process_results(self, results);
+                return;
+            }
+
+            let num_cpus = thread::available_parallelism()
+                .map(|p| p.get())
+                .unwrap_or(1);
+            let chunk_size = (total_indices + num_cpus as u32 - 1) / num_cpus as u32;
+            let descriptor = Arc::new(descriptor.clone());
+            let mut handles = Vec::with_capacity(num_cpus);
+
+            for i in 0..num_cpus {
+                let start = next_store_index + (i as u32 * chunk_size);
+                if start >= end_index {
+                    break;
+                }
+
+                let end = (start + chunk_size).min(end_index);
+                let descriptor_clone = Arc::clone(&descriptor);
+
+                let handle = thread::spawn(move || {
+                    let mut thread_results = Vec::with_capacity((end - start) as usize);
+
+                    for (new_index, new_spk) in
+                        SpkIterator::new_with_range(&*descriptor_clone, start..end)
+                    {
+                        thread_results.push((new_index, new_spk));
+                    }
+
+                    thread_results
+                });
+
+                handles.push(handle);
+            }
+
+            let mut all_results = Vec::new();
+            for handle in handles {
+                if let Ok(thread_results) = handle.join() {
+                    all_results.extend(thread_results);
+                }
+            }
+
+            // Sort results by index to ensure they're processed in order
+            all_results.sort_by_key(|(index, _)| *index);
+
+            process_results(self, all_results);
         }
     }
 
diff --git a/crates/chain/tests/test_keychain_txout_index.rs b/crates/chain/tests/test_keychain_txout_index.rs
index 8b299b896..8a3eb28c4 100644
--- a/crates/chain/tests/test_keychain_txout_index.rs
+++ b/crates/chain/tests/test_keychain_txout_index.rs
@@ -542,10 +542,10 @@ fn lookahead_to_target() {
         },
         TestCase {
             lookahead: 13,
-            external_last_revealed: Some(100),
-            internal_last_revealed: Some(21),
-            internal_target: Some(120),
-            external_target: Some(130),
+            external_last_revealed: Some(1100),
+            internal_last_revealed: Some(1200),
+            internal_target: Some(1110),
+            external_target: Some(1120),
         },
     ];