From 28240f47128012b1b756c617714ebf40548aec81 Mon Sep 17 00:00:00 2001
From: Eitan Seri-Levi <eserilev@ucsc.edu>
Date: Sun, 24 May 2026 16:51:57 +0300
Subject: [PATCH] calculate head block number for gloas

---
 beacon_node/beacon_chain/src/beacon_chain.rs   |  8 ++++----
 beacon_node/beacon_chain/src/canonical_head.rs | 13 ++++++++++++-
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/beacon_node/beacon_chain/src/beacon_chain.rs b/beacon_node/beacon_chain/src/beacon_chain.rs
index db8f55a18a..8c0363608a 100644
--- a/beacon_node/beacon_chain/src/beacon_chain.rs
+++ b/beacon_node/beacon_chain/src/beacon_chain.rs
@@ -5055,16 +5055,16 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             return Ok(None);
         };
 
-        // TODO(gloas) not sure what to do here see this issue
-        // https://github.com/sigp/lighthouse/issues/8817
         let (prev_randao, parent_block_number) = if self
             .spec
             .fork_name_at_slot::<T::EthSpec>(proposal_slot)
             .gloas_enabled()
         {
-            (cached_head.head_random()?, None)
+            (
+                cached_head.head_random()?,
+                cached_head.head_block_number_gloas(),
+            )
         } else {
-            // Get the `prev_randao` and parent block number.
             let head_block_number = cached_head.head_block_number()?;
             if proposer_head == head_parent_block_root {
                 (
diff --git a/beacon_node/beacon_chain/src/canonical_head.rs b/beacon_node/beacon_chain/src/canonical_head.rs
index b3ab2e6975..ba89703fb9 100644
--- a/beacon_node/beacon_chain/src/canonical_head.rs
+++ b/beacon_node/beacon_chain/src/canonical_head.rs
@@ -178,7 +178,7 @@ impl<E: EthSpec> CachedHead<E> {
 
     /// Returns the execution block number of the block at the head of the chain.
     ///
-    /// Returns an error if the chain is prior to Bellatrix.
+    /// Returns an error if the chain is prior to Bellatrix or post-Gloas
     pub fn head_block_number(&self) -> Result<u64, BeaconStateError> {
         self.snapshot
             .beacon_block
@@ -187,6 +187,17 @@ impl<E: EthSpec> CachedHead<E> {
             .map(|payload| payload.block_number())
     }
 
+    /// Returns the execution block number of the block at the head of the chain.
+    ///
+    /// Returns an error if the chain is prior to Gloas.
+    pub fn head_block_number_gloas(&self) -> Result<u64, BeaconStateError> {
+        self.snapshot
+            .execution_envelope
+            .as_ref()
+            .map(|envelope| envelope.message.payload.block_number)
+            .ok()
+    }
+
     /// Returns the active validator count for the current epoch of the head state.
     ///
     /// Should only return `None` if the caches have not been built on the head state (this should