diff --git a/beacon_node/beacon_chain/src/schema_change.rs b/beacon_node/beacon_chain/src/schema_change.rs
index ed82143c38..fa2ab70d21 100644
--- a/beacon_node/beacon_chain/src/schema_change.rs
+++ b/beacon_node/beacon_chain/src/schema_change.rs
@@ -1,5 +1,8 @@
 //! Utilities for managing database schema changes.
+mod migration_schema_v29;
+
 use crate::beacon_chain::BeaconChainTypes;
+use migration_schema_v29::{downgrade_from_v29, upgrade_to_v29};
 use std::sync::Arc;
 use store::Error as StoreError;
 use store::hot_cold_store::{HotColdDB, HotColdDBError};
@@ -10,13 +13,23 @@ use store::metadata::{CURRENT_SCHEMA_VERSION, SchemaVersion};
 /// All migrations for schema versions up to and including v28 have been removed. Nodes on live
 /// networks are already running v28, so only the current version check remains.
 pub fn migrate_schema<T: BeaconChainTypes>(
-    _db: Arc<HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>>,
+    db: Arc<HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>>,
     from: SchemaVersion,
     to: SchemaVersion,
 ) -> Result<(), StoreError> {
     match (from, to) {
         // Migrating from the current schema version to itself is always OK, a no-op.
         (_, _) if from == to && to == CURRENT_SCHEMA_VERSION => Ok(()),
+        // Upgrade from v28 to v29.
+        (SchemaVersion(28), SchemaVersion(29)) => {
+            upgrade_to_v29::<T>(&db)?;
+            db.store_schema_version_atomically(to, vec![])
+        }
+        // Downgrade from v29 to v28.
+        (SchemaVersion(29), SchemaVersion(28)) => {
+            downgrade_from_v29::<T>(&db)?;
+            db.store_schema_version_atomically(to, vec![])
+        }
         // Anything else is an error.
         (_, _) => Err(HotColdDBError::UnsupportedSchemaVersion {
             target_version: to,
diff --git a/beacon_node/beacon_chain/src/schema_change/migration_schema_v29.rs b/beacon_node/beacon_chain/src/schema_change/migration_schema_v29.rs
new file mode 100644
index 0000000000..c88a1cada1
--- /dev/null
+++ b/beacon_node/beacon_chain/src/schema_change/migration_schema_v29.rs
@@ -0,0 +1,100 @@
+use crate::beacon_chain::BeaconChainTypes;
+use crate::persisted_fork_choice::{PersistedForkChoiceV28, PersistedForkChoiceV29};
+use ssz::Decode;
+use store::hot_cold_store::HotColdDB;
+use store::{DBColumn, Error as StoreError, KeyValueStore};
+use types::{EthSpec, Hash256};
+
+/// The key used to store the fork choice in the database.
+const FORK_CHOICE_DB_KEY: Hash256 = Hash256::ZERO;
+
+/// Upgrade from schema v28 to v29 (no-op).
+///
+/// Fails if the persisted fork choice contains any V17 (pre-Gloas) proto nodes at or after the
+/// Gloas fork slot. Such nodes indicate the node synced a broken sidechain with Gloas disabled
+/// and would not be able to sync the v29 chain.
+pub fn upgrade_to_v29<T: BeaconChainTypes>(
+    db: &HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>,
+) -> Result<(), StoreError> {
+    let gloas_fork_slot = db
+        .spec
+        .gloas_fork_epoch
+        .map(|epoch| epoch.start_slot(T::EthSpec::slots_per_epoch()));
+
+    // If Gloas is not configured, the upgrade is a safe no-op.
+    let Some(gloas_fork_slot) = gloas_fork_slot else {
+        return Ok(());
+    };
+
+    // Load the persisted fork choice (v28 format, uncompressed SSZ).
+    let Some(fc_bytes) = db
+        .hot_db
+        .get_bytes(DBColumn::ForkChoice, FORK_CHOICE_DB_KEY.as_slice())?
+    else {
+        return Ok(());
+    };
+
+    let persisted_v28 =
+        PersistedForkChoiceV28::from_ssz_bytes(&fc_bytes).map_err(StoreError::SszDecodeError)?;
+
+    // In v28 format, all nodes are ProtoNodeV17. Check if any are at/after the Gloas fork slot.
+    let bad_node = persisted_v28
+        .fork_choice_v28
+        .proto_array_v28
+        .nodes
+        .iter()
+        .find(|node| node.slot >= gloas_fork_slot);
+
+    if let Some(node) = bad_node {
+        return Err(StoreError::MigrationError(format!(
+            "cannot upgrade from v28 to v29: found V17 proto node at slot {} (root: {:?}) \
+             which is at or after the Gloas fork slot {}. This node has synced a chain with \
+             Gloas disabled and cannot be upgraded. Please resync from scratch.",
+            node.slot, node.root, gloas_fork_slot,
+        )));
+    }
+
+    Ok(())
+}
+
+/// Downgrade from schema v29 to v28 (no-op).
+///
+/// Fails if the persisted fork choice contains any V29 proto nodes, as these contain
+/// payload-specific fields that cannot be losslessly converted back to V17 format.
+pub fn downgrade_from_v29<T: BeaconChainTypes>(
+    db: &HotColdDB<T::EthSpec, T::HotStore, T::ColdStore>,
+) -> Result<(), StoreError> {
+    // Load the persisted fork choice (v29 format, compressed).
+    let Some(fc_bytes) = db
+        .hot_db
+        .get_bytes(DBColumn::ForkChoice, FORK_CHOICE_DB_KEY.as_slice())?
+    else {
+        return Ok(());
+    };
+
+    let persisted_v29 =
+        PersistedForkChoiceV29::from_bytes(&fc_bytes, db.get_config()).map_err(|e| {
+            StoreError::MigrationError(format!(
+                "cannot downgrade from v29 to v28: failed to decode fork choice: {:?}",
+                e
+            ))
+        })?;
+
+    let has_v29_node = persisted_v29
+        .fork_choice
+        .proto_array
+        .nodes
+        .iter()
+        .any(|node| matches!(node, proto_array::core::ProtoNode::V29(_)));
+
+    if has_v29_node {
+        return Err(StoreError::MigrationError(
+            "cannot downgrade from v29 to v28: the persisted fork choice contains V29 proto \
+             nodes which cannot be losslessly converted to V17 format. The Gloas-specific \
+             payload data would be lost."
+                .to_string(),
+        ));
+    }
+
+    Ok(())
+}