diff --git a/beacon/blsync/block_sync.go b/beacon/blsync/block_sync.go
index 3ab156354d..ff689a922f 100755
--- a/beacon/blsync/block_sync.go
+++ b/beacon/blsync/block_sync.go
@@ -41,7 +41,7 @@ type beaconBlockSync struct {
 
 type headTracker interface {
 	PrefetchHead() types.HeadInfo
-	ValidatedHead() (types.SignedHeader, bool)
+	ValidatedOptimistic() (types.OptimisticUpdate, bool)
 	ValidatedFinality() (types.FinalityUpdate, bool)
 }
 
@@ -66,6 +66,7 @@ func (s *beaconBlockSync) Process(requester request.Requester, events []request.
 		case request.EvResponse, request.EvFail, request.EvTimeout:
 			sid, req, resp := event.RequestInfo()
 			blockRoot := common.Hash(req.(sync.ReqBeaconBlock))
+			log.Debug("Beacon block event", "type", event.Type.Name, "hash", blockRoot)
 			if resp != nil {
 				s.recentBlocks.Add(blockRoot, resp.(*types.BeaconBlock))
 			}
@@ -80,8 +81,8 @@ func (s *beaconBlockSync) Process(requester request.Requester, events []request.
 	}
 	s.updateEventFeed()
 	// request validated head block if unavailable and not yet requested
-	if vh, ok := s.headTracker.ValidatedHead(); ok {
-		s.tryRequestBlock(requester, vh.Header.Hash(), false)
+	if vh, ok := s.headTracker.ValidatedOptimistic(); ok {
+		s.tryRequestBlock(requester, vh.Attested.Hash(), false)
 	}
 	// request prefetch head if the given server has announced it
 	if prefetchHead := s.headTracker.PrefetchHead().BlockRoot; prefetchHead != (common.Hash{}) {
@@ -114,12 +115,12 @@ func blockHeadInfo(block *types.BeaconBlock) types.HeadInfo {
 }
 
 func (s *beaconBlockSync) updateEventFeed() {
-	head, ok := s.headTracker.ValidatedHead()
+	optimistic, ok := s.headTracker.ValidatedOptimistic()
 	if !ok {
 		return
 	}
 
-	validatedHead := head.Header.Hash()
+	validatedHead := optimistic.Attested.Hash()
 	headBlock, ok := s.recentBlocks.Get(validatedHead)
 	if !ok {
 		return
@@ -127,7 +128,7 @@ func (s *beaconBlockSync) updateEventFeed() {
 
 	var finalizedHash common.Hash
 	if finality, ok := s.headTracker.ValidatedFinality(); ok {
-		he := head.Header.Epoch()
+		he := optimistic.Attested.Epoch()
 		fe := finality.Attested.Header.Epoch()
 		switch {
 		case he == fe:
@@ -135,10 +136,9 @@ func (s *beaconBlockSync) updateEventFeed() {
 		case he < fe:
 			return
 		case he == fe+1:
-			parent, ok := s.recentBlocks.Get(head.Header.ParentRoot)
+			parent, ok := s.recentBlocks.Get(optimistic.Attested.ParentRoot)
 			if !ok || parent.Slot()/params.EpochLength == fe {
 				return // head is at first slot of next epoch, wait for finality update
-				//TODO: try to fetch finality update directly if subscription does not deliver
 			}
 		}
 	}
@@ -156,7 +156,7 @@ func (s *beaconBlockSync) updateEventFeed() {
 		return
 	}
 	s.chainHeadFeed.Send(types.ChainHeadEvent{
-		BeaconHead: head.Header,
+		BeaconHead: optimistic.Attested.Header,
 		Block:      execBlock,
 		Finalized:  finalizedHash,
 	})
diff --git a/beacon/blsync/block_sync_test.go b/beacon/blsync/block_sync_test.go
index 0525e95a89..3d3b9e5e8d 100644
--- a/beacon/blsync/block_sync_test.go
+++ b/beacon/blsync/block_sync_test.go
@@ -140,8 +140,12 @@ func (h *testHeadTracker) PrefetchHead() types.HeadInfo {
 	return h.prefetch
 }
 
-func (h *testHeadTracker) ValidatedHead() (types.SignedHeader, bool) {
-	return h.validated, h.validated.Header != (types.Header{})
+func (h *testHeadTracker) ValidatedOptimistic() (types.OptimisticUpdate, bool) {
+	return types.OptimisticUpdate{
+		Attested:      types.HeaderWithExecProof{Header: h.validated.Header},
+		Signature:     h.validated.Signature,
+		SignatureSlot: h.validated.SignatureSlot,
+	}, h.validated.Header != (types.Header{})
 }
 
 // TODO add test case for finality
diff --git a/beacon/blsync/engineclient.go b/beacon/blsync/engineclient.go
index 5a2d292a7d..97ef6f5cb8 100644
--- a/beacon/blsync/engineclient.go
+++ b/beacon/blsync/engineclient.go
@@ -62,6 +62,7 @@ func (ec *engineClient) updateLoop(headCh <-chan types.ChainHeadEvent) {
 	for {
 		select {
 		case <-ec.rootCtx.Done():
+			log.Debug("Stopping engine API update loop")
 			return
 
 		case event := <-headCh:
@@ -73,12 +74,14 @@ func (ec *engineClient) updateLoop(headCh <-chan types.ChainHeadEvent) {
 			fork := ec.config.ForkAtEpoch(event.BeaconHead.Epoch())
 			forkName := strings.ToLower(fork.Name)
 
+			log.Debug("Calling NewPayload", "number", event.Block.NumberU64(), "hash", event.Block.Hash())
 			if status, err := ec.callNewPayload(forkName, event); err == nil {
 				log.Info("Successful NewPayload", "number", event.Block.NumberU64(), "hash", event.Block.Hash(), "status", status)
 			} else {
 				log.Error("Failed NewPayload", "number", event.Block.NumberU64(), "hash", event.Block.Hash(), "error", err)
 			}
 
+			log.Debug("Calling ForkchoiceUpdated", "head", event.Block.Hash())
 			if status, err := ec.callForkchoiceUpdated(forkName, event); err == nil {
 				log.Info("Successful ForkchoiceUpdated", "head", event.Block.Hash(), "status", status)
 			} else {
diff --git a/beacon/light/api/api_server.go b/beacon/light/api/api_server.go
index 4b885cb8e1..2579854d82 100755
--- a/beacon/light/api/api_server.go
+++ b/beacon/light/api/api_server.go
@@ -46,13 +46,13 @@ func (s *ApiServer) Subscribe(eventCallback func(event request.Event)) {
 			log.Debug("New head received", "slot", slot, "blockRoot", blockRoot)
 			eventCallback(request.Event{Type: sync.EvNewHead, Data: types.HeadInfo{Slot: slot, BlockRoot: blockRoot}})
 		},
-		OnSignedHead: func(head types.SignedHeader) {
-			log.Debug("New signed head received", "slot", head.Header.Slot, "blockRoot", head.Header.Hash(), "signerCount", head.Signature.SignerCount())
-			eventCallback(request.Event{Type: sync.EvNewSignedHead, Data: head})
+		OnOptimistic: func(update types.OptimisticUpdate) {
+			log.Debug("New optimistic update received", "slot", update.Attested.Slot, "blockRoot", update.Attested.Hash(), "signerCount", update.Signature.SignerCount())
+			eventCallback(request.Event{Type: sync.EvNewOptimisticUpdate, Data: update})
 		},
-		OnFinality: func(head types.FinalityUpdate) {
-			log.Debug("New finality update received", "slot", head.Attested.Slot, "blockRoot", head.Attested.Hash(), "signerCount", head.Signature.SignerCount())
-			eventCallback(request.Event{Type: sync.EvNewFinalityUpdate, Data: head})
+		OnFinality: func(update types.FinalityUpdate) {
+			log.Debug("New finality update received", "slot", update.Attested.Slot, "blockRoot", update.Attested.Hash(), "signerCount", update.Signature.SignerCount())
+			eventCallback(request.Event{Type: sync.EvNewFinalityUpdate, Data: update})
 		},
 		OnError: func(err error) {
 			log.Warn("Head event stream error", "err", err)
@@ -83,6 +83,9 @@ func (s *ApiServer) SendRequest(id request.ID, req request.Request) {
 		case sync.ReqBeaconBlock:
 			log.Debug("Beacon API: requesting block", "reqid", id, "hash", common.Hash(data))
 			resp, err = s.api.GetBeaconBlock(common.Hash(data))
+		case sync.ReqFinality:
+			log.Debug("Beacon API: requesting finality update")
+			resp, err = s.api.GetFinalityUpdate()
 		default:
 		}
 
@@ -90,6 +93,7 @@ func (s *ApiServer) SendRequest(id request.ID, req request.Request) {
 			log.Warn("Beacon API request failed", "type", reflect.TypeOf(req), "reqid", id, "err", err)
 			s.eventCallback(request.Event{Type: request.EvFail, Data: request.RequestResponse{ID: id, Request: req}})
 		} else {
+			log.Debug("Beacon API request answered", "type", reflect.TypeOf(req), "reqid", id)
 			s.eventCallback(request.Event{Type: request.EvResponse, Data: request.RequestResponse{ID: id, Request: req, Response: resp}})
 		}
 	}()
diff --git a/beacon/light/api/light_api.go b/beacon/light/api/light_api.go
index 6892407caf..903db57344 100755
--- a/beacon/light/api/light_api.go
+++ b/beacon/light/api/light_api.go
@@ -32,6 +32,7 @@ import (
 	"github.com/ethereum/go-ethereum/beacon/types"
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/ethereum/go-ethereum/log"
 )
 
 var (
@@ -184,46 +185,56 @@ func (api *BeaconLightApi) GetBestUpdatesAndCommittees(firstPeriod, count uint64
 	return updates, committees, nil
 }
 
-// GetOptimisticHeadUpdate fetches a signed header based on the latest available
-// optimistic update. Note that the signature should be verified by the caller
-// as its validity depends on the update chain.
+// GetOptimisticUpdate fetches the latest available optimistic update.
+// Note that the signature should be verified by the caller as its validity
+// depends on the update chain.
 //
 // See data structure definition here:
 // https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/light-client/sync-protocol.md#lightclientoptimisticupdate
-func (api *BeaconLightApi) GetOptimisticHeadUpdate() (types.SignedHeader, error) {
+func (api *BeaconLightApi) GetOptimisticUpdate() (types.OptimisticUpdate, error) {
 	resp, err := api.httpGet("/eth/v1/beacon/light_client/optimistic_update")
 	if err != nil {
-		return types.SignedHeader{}, err
+		return types.OptimisticUpdate{}, err
 	}
-	return decodeOptimisticHeadUpdate(resp)
+	return decodeOptimisticUpdate(resp)
 }
 
-func decodeOptimisticHeadUpdate(enc []byte) (types.SignedHeader, error) {
+func decodeOptimisticUpdate(enc []byte) (types.OptimisticUpdate, error) {
 	var data struct {
-		Data struct {
-			Header        jsonBeaconHeader    `json:"attested_header"`
-			Aggregate     types.SyncAggregate `json:"sync_aggregate"`
-			SignatureSlot common.Decimal      `json:"signature_slot"`
+		Version string
+		Data    struct {
+			Attested      jsonHeaderWithExecProof `json:"attested_header"`
+			Aggregate     types.SyncAggregate     `json:"sync_aggregate"`
+			SignatureSlot common.Decimal          `json:"signature_slot"`
 		} `json:"data"`
 	}
 	if err := json.Unmarshal(enc, &data); err != nil {
-		return types.SignedHeader{}, err
+		return types.OptimisticUpdate{}, err
+	}
+	// Decode the execution payload headers.
+	attestedExecHeader, err := types.ExecutionHeaderFromJSON(data.Version, data.Data.Attested.Execution)
+	if err != nil {
+		return types.OptimisticUpdate{}, fmt.Errorf("invalid attested header: %v", err)
 	}
-	if data.Data.Header.Beacon.StateRoot == (common.Hash{}) {
+	if data.Data.Attested.Beacon.StateRoot == (common.Hash{}) {
 		// workaround for different event encoding format in Lodestar
 		if err := json.Unmarshal(enc, &data.Data); err != nil {
-			return types.SignedHeader{}, err
+			return types.OptimisticUpdate{}, err
 		}
 	}
 
 	if len(data.Data.Aggregate.Signers) != params.SyncCommitteeBitmaskSize {
-		return types.SignedHeader{}, errors.New("invalid sync_committee_bits length")
+		return types.OptimisticUpdate{}, errors.New("invalid sync_committee_bits length")
 	}
 	if len(data.Data.Aggregate.Signature) != params.BLSSignatureSize {
-		return types.SignedHeader{}, errors.New("invalid sync_committee_signature length")
+		return types.OptimisticUpdate{}, errors.New("invalid sync_committee_signature length")
 	}
-	return types.SignedHeader{
-		Header:        data.Data.Header.Beacon,
+	return types.OptimisticUpdate{
+		Attested: types.HeaderWithExecProof{
+			Header:        data.Data.Attested.Beacon,
+			PayloadHeader: attestedExecHeader,
+			PayloadBranch: data.Data.Attested.ExecutionBranch,
+		},
 		Signature:     data.Data.Aggregate,
 		SignatureSlot: uint64(data.Data.SignatureSlot),
 	}, nil
@@ -411,7 +422,7 @@ func decodeHeadEvent(enc []byte) (uint64, common.Hash, error) {
 
 type HeadEventListener struct {
 	OnNewHead    func(slot uint64, blockRoot common.Hash)
-	OnSignedHead func(head types.SignedHeader)
+	OnOptimistic func(head types.OptimisticUpdate)
 	OnFinality   func(head types.FinalityUpdate)
 	OnError      func(err error)
 }
@@ -449,21 +460,35 @@ func (api *BeaconLightApi) StartHeadListener(listener HeadEventListener) func()
 		defer wg.Done()
 
 		// Request initial data.
+		log.Trace("Requesting initial head header")
 		if head, _, _, err := api.GetHeader(common.Hash{}); err == nil {
+			log.Trace("Retrieved initial head header", "slot", head.Slot, "hash", head.Hash())
 			listener.OnNewHead(head.Slot, head.Hash())
+		} else {
+			log.Debug("Failed to retrieve initial head header", "error", err)
 		}
-		if signedHead, err := api.GetOptimisticHeadUpdate(); err == nil {
-			listener.OnSignedHead(signedHead)
+		log.Trace("Requesting initial optimistic update")
+		if optimisticUpdate, err := api.GetOptimisticUpdate(); err == nil {
+			log.Trace("Retrieved initial optimistic update", "slot", optimisticUpdate.Attested.Slot, "hash", optimisticUpdate.Attested.Hash())
+			listener.OnOptimistic(optimisticUpdate)
+		} else {
+			log.Debug("Failed to retrieve initial optimistic update", "error", err)
 		}
+		log.Trace("Requesting initial finality update")
 		if finalityUpdate, err := api.GetFinalityUpdate(); err == nil {
+			log.Trace("Retrieved initial finality update", "slot", finalityUpdate.Finalized.Slot, "hash", finalityUpdate.Finalized.Hash())
 			listener.OnFinality(finalityUpdate)
+		} else {
+			log.Debug("Failed to retrieve initial finality update", "error", err)
 		}
 
+		log.Trace("Starting event stream processing loop")
 		// Receive the stream.
 		var stream *eventsource.Stream
 		select {
 		case stream = <-streamCh:
 		case <-ctx.Done():
+			log.Trace("Stopping event stream processing loop")
 			return
 		}
 
@@ -474,8 +499,10 @@ func (api *BeaconLightApi) StartHeadListener(listener HeadEventListener) func()
 
 			case event, ok := <-stream.Events:
 				if !ok {
+					log.Trace("Event stream closed")
 					return
 				}
+				log.Trace("New event received from event stream", "type", event.Event())
 				switch event.Event() {
 				case "head":
 					slot, blockRoot, err := decodeHeadEvent([]byte(event.Data()))
@@ -485,9 +512,9 @@ func (api *BeaconLightApi) StartHeadListener(listener HeadEventListener) func()
 						listener.OnError(fmt.Errorf("error decoding head event: %v", err))
 					}
 				case "light_client_optimistic_update":
-					signedHead, err := decodeOptimisticHeadUpdate([]byte(event.Data()))
+					optimisticUpdate, err := decodeOptimisticUpdate([]byte(event.Data()))
 					if err == nil {
-						listener.OnSignedHead(signedHead)
+						listener.OnOptimistic(optimisticUpdate)
 					} else {
 						listener.OnError(fmt.Errorf("error decoding optimistic update event: %v", err))
 					}
@@ -521,7 +548,8 @@ func (api *BeaconLightApi) StartHeadListener(listener HeadEventListener) func()
 // established. It can only return nil when the context is canceled.
 func (api *BeaconLightApi) startEventStream(ctx context.Context, listener *HeadEventListener) *eventsource.Stream {
 	for retry := true; retry; retry = ctxSleep(ctx, 5*time.Second) {
-		path := "/eth/v1/events?topics=head&topics=light_client_optimistic_update&topics=light_client_finality_update"
+		path := "/eth/v1/events?topics=head&topics=light_client_finality_update&topics=light_client_optimistic_update"
+		log.Trace("Sending event subscription request")
 		req, err := http.NewRequestWithContext(ctx, "GET", api.url+path, nil)
 		if err != nil {
 			listener.OnError(fmt.Errorf("error creating event subscription request: %v", err))
@@ -535,6 +563,7 @@ func (api *BeaconLightApi) startEventStream(ctx context.Context, listener *HeadE
 			listener.OnError(fmt.Errorf("error creating event subscription: %v", err))
 			continue
 		}
+		log.Trace("Successfully created event stream")
 		return stream
 	}
 	return nil
diff --git a/beacon/light/head_tracker.go b/beacon/light/head_tracker.go
index 6036322f01..7ef93fecce 100644
--- a/beacon/light/head_tracker.go
+++ b/beacon/light/head_tracker.go
@@ -29,15 +29,15 @@ import (
 // which is the (not necessarily validated) head announced by the majority of
 // servers.
 type HeadTracker struct {
-	lock              sync.RWMutex
-	committeeChain    *CommitteeChain
-	minSignerCount    int
-	signedHead        types.SignedHeader
-	hasSignedHead     bool
-	finalityUpdate    types.FinalityUpdate
-	hasFinalityUpdate bool
-	prefetchHead      types.HeadInfo
-	changeCounter     uint64
+	lock                sync.RWMutex
+	committeeChain      *CommitteeChain
+	minSignerCount      int
+	optimisticUpdate    types.OptimisticUpdate
+	hasOptimisticUpdate bool
+	finalityUpdate      types.FinalityUpdate
+	hasFinalityUpdate   bool
+	prefetchHead        types.HeadInfo
+	changeCounter       uint64
 }
 
 // NewHeadTracker creates a new HeadTracker.
@@ -48,15 +48,15 @@ func NewHeadTracker(committeeChain *CommitteeChain, minSignerCount int) *HeadTra
 	}
 }
 
-// ValidatedHead returns the latest validated head.
-func (h *HeadTracker) ValidatedHead() (types.SignedHeader, bool) {
+// ValidatedOptimistic returns the latest validated optimistic update.
+func (h *HeadTracker) ValidatedOptimistic() (types.OptimisticUpdate, bool) {
 	h.lock.RLock()
 	defer h.lock.RUnlock()
 
-	return h.signedHead, h.hasSignedHead
+	return h.optimisticUpdate, h.hasOptimisticUpdate
 }
 
-// ValidatedFinality returns the latest validated finality.
+// ValidatedFinality returns the latest validated finality update.
 func (h *HeadTracker) ValidatedFinality() (types.FinalityUpdate, bool) {
 	h.lock.RLock()
 	defer h.lock.RUnlock()
@@ -64,26 +64,36 @@ func (h *HeadTracker) ValidatedFinality() (types.FinalityUpdate, bool) {
 	return h.finalityUpdate, h.hasFinalityUpdate
 }
 
-// ValidateHead validates the given signed head. If the head is successfully validated
-// and it is better than the old validated head (higher slot or same slot and more
-// signers) then ValidatedHead is updated. The boolean return flag signals if
-// ValidatedHead has been changed.
-func (h *HeadTracker) ValidateHead(head types.SignedHeader) (bool, error) {
+// ValidateOptimistic validates the given optimistic update. If the update is
+// successfully validated and it is better than the old validated update (higher
+// slot or same slot and more signers) then ValidatedOptimistic is updated.
+// The boolean return flag signals if ValidatedOptimistic has been changed.
+func (h *HeadTracker) ValidateOptimistic(update types.OptimisticUpdate) (bool, error) {
 	h.lock.Lock()
 	defer h.lock.Unlock()
 
-	replace, err := h.validate(head, h.signedHead)
+	if err := update.Validate(); err != nil {
+		return false, err
+	}
+	replace, err := h.validate(update.SignedHeader(), h.optimisticUpdate.SignedHeader())
 	if replace {
-		h.signedHead, h.hasSignedHead = head, true
+		h.optimisticUpdate, h.hasOptimisticUpdate = update, true
 		h.changeCounter++
 	}
 	return replace, err
 }
 
+// ValidateFinality validates the given finality update. If the update is
+// successfully validated and it is better than the old validated update (higher
+// slot or same slot and more signers) then ValidatedFinality is updated.
+// The boolean return flag signals if ValidatedFinality has been changed.
 func (h *HeadTracker) ValidateFinality(update types.FinalityUpdate) (bool, error) {
 	h.lock.Lock()
 	defer h.lock.Unlock()
 
+	if err := update.Validate(); err != nil {
+		return false, err
+	}
 	replace, err := h.validate(update.SignedHeader(), h.finalityUpdate.SignedHeader())
 	if replace {
 		h.finalityUpdate, h.hasFinalityUpdate = update, true
@@ -142,6 +152,7 @@ func (h *HeadTracker) SetPrefetchHead(head types.HeadInfo) {
 	h.changeCounter++
 }
 
+// ChangeCounter implements request.targetData
 func (h *HeadTracker) ChangeCounter() uint64 {
 	h.lock.RLock()
 	defer h.lock.RUnlock()
diff --git a/beacon/light/sync/head_sync.go b/beacon/light/sync/head_sync.go
index 5ccc2e18a2..dd05d39588 100644
--- a/beacon/light/sync/head_sync.go
+++ b/beacon/light/sync/head_sync.go
@@ -19,11 +19,13 @@ package sync
 import (
 	"github.com/ethereum/go-ethereum/beacon/light/request"
 	"github.com/ethereum/go-ethereum/beacon/types"
+	"github.com/ethereum/go-ethereum/log"
 )
 
 type headTracker interface {
-	ValidateHead(head types.SignedHeader) (bool, error)
+	ValidateOptimistic(update types.OptimisticUpdate) (bool, error)
 	ValidateFinality(head types.FinalityUpdate) (bool, error)
+	ValidatedFinality() (types.FinalityUpdate, bool)
 	SetPrefetchHead(head types.HeadInfo)
 }
 
@@ -33,16 +35,17 @@ type headTracker interface {
 // It can also postpone the validation of the latest announced signed head
 // until the committee chain is synced up to at least the required period.
 type HeadSync struct {
-	headTracker         headTracker
-	chain               committeeChain
-	nextSyncPeriod      uint64
-	chainInit           bool
-	unvalidatedHeads    map[request.Server]types.SignedHeader
-	unvalidatedFinality map[request.Server]types.FinalityUpdate
-	serverHeads         map[request.Server]types.HeadInfo
-	headServerCount     map[types.HeadInfo]headServerCount
-	headCounter         uint64
-	prefetchHead        types.HeadInfo
+	headTracker           headTracker
+	chain                 committeeChain
+	nextSyncPeriod        uint64
+	chainInit             bool
+	unvalidatedOptimistic map[request.Server]types.OptimisticUpdate
+	unvalidatedFinality   map[request.Server]types.FinalityUpdate
+	serverHeads           map[request.Server]types.HeadInfo
+	reqFinalityEpoch      map[request.Server]uint64 // next epoch to request finality update
+	headServerCount       map[types.HeadInfo]headServerCount
+	headCounter           uint64
+	prefetchHead          types.HeadInfo
 }
 
 // headServerCount is associated with most recently seen head infos; it counts
@@ -57,75 +60,98 @@ type headServerCount struct {
 // NewHeadSync creates a new HeadSync.
 func NewHeadSync(headTracker headTracker, chain committeeChain) *HeadSync {
 	s := &HeadSync{
-		headTracker:         headTracker,
-		chain:               chain,
-		unvalidatedHeads:    make(map[request.Server]types.SignedHeader),
-		unvalidatedFinality: make(map[request.Server]types.FinalityUpdate),
-		serverHeads:         make(map[request.Server]types.HeadInfo),
-		headServerCount:     make(map[types.HeadInfo]headServerCount),
+		headTracker:           headTracker,
+		chain:                 chain,
+		unvalidatedOptimistic: make(map[request.Server]types.OptimisticUpdate),
+		unvalidatedFinality:   make(map[request.Server]types.FinalityUpdate),
+		serverHeads:           make(map[request.Server]types.HeadInfo),
+		headServerCount:       make(map[types.HeadInfo]headServerCount),
+		reqFinalityEpoch:      make(map[request.Server]uint64),
 	}
 	return s
 }
 
 // Process implements request.Module.
 func (s *HeadSync) Process(requester request.Requester, events []request.Event) {
+	nextPeriod, chainInit := s.chain.NextSyncPeriod()
+	if nextPeriod != s.nextSyncPeriod || chainInit != s.chainInit {
+		s.nextSyncPeriod, s.chainInit = nextPeriod, chainInit
+		s.processUnvalidatedUpdates()
+	}
+
 	for _, event := range events {
 		switch event.Type {
 		case EvNewHead:
 			s.setServerHead(event.Server, event.Data.(types.HeadInfo))
-		case EvNewSignedHead:
-			s.newSignedHead(event.Server, event.Data.(types.SignedHeader))
+		case EvNewOptimisticUpdate:
+			update := event.Data.(types.OptimisticUpdate)
+			s.newOptimisticUpdate(event.Server, update)
+			epoch := update.Attested.Epoch()
+			if epoch < s.reqFinalityEpoch[event.Server] {
+				continue
+			}
+			if finality, ok := s.headTracker.ValidatedFinality(); ok && finality.Attested.Header.Epoch() >= epoch {
+				continue
+			}
+			requester.Send(event.Server, ReqFinality{})
+			s.reqFinalityEpoch[event.Server] = epoch + 1
 		case EvNewFinalityUpdate:
 			s.newFinalityUpdate(event.Server, event.Data.(types.FinalityUpdate))
+		case request.EvResponse:
+			_, _, resp := event.RequestInfo()
+			s.newFinalityUpdate(event.Server, resp.(types.FinalityUpdate))
 		case request.EvUnregistered:
 			s.setServerHead(event.Server, types.HeadInfo{})
 			delete(s.serverHeads, event.Server)
-			delete(s.unvalidatedHeads, event.Server)
+			delete(s.unvalidatedOptimistic, event.Server)
+			delete(s.unvalidatedFinality, event.Server)
 		}
 	}
-
-	nextPeriod, chainInit := s.chain.NextSyncPeriod()
-	if nextPeriod != s.nextSyncPeriod || chainInit != s.chainInit {
-		s.nextSyncPeriod, s.chainInit = nextPeriod, chainInit
-		s.processUnvalidated()
-	}
 }
 
-// newSignedHead handles received signed head; either validates it if the chain
-// is properly synced or stores it for further validation.
-func (s *HeadSync) newSignedHead(server request.Server, signedHead types.SignedHeader) {
-	if !s.chainInit || types.SyncPeriod(signedHead.SignatureSlot) > s.nextSyncPeriod {
-		s.unvalidatedHeads[server] = signedHead
+// newOptimisticUpdate handles received optimistic update; either validates it if
+// the chain is properly synced or stores it for further validation.
+func (s *HeadSync) newOptimisticUpdate(server request.Server, optimisticUpdate types.OptimisticUpdate) {
+	if !s.chainInit || types.SyncPeriod(optimisticUpdate.SignatureSlot) > s.nextSyncPeriod {
+		s.unvalidatedOptimistic[server] = optimisticUpdate
 		return
 	}
-	s.headTracker.ValidateHead(signedHead)
+	if _, err := s.headTracker.ValidateOptimistic(optimisticUpdate); err != nil {
+		log.Debug("Error validating optimistic update", "error", err)
+	}
 }
 
-// newFinalityUpdate handles received finality update; either validates it if the chain
-// is properly synced or stores it for further validation.
+// newFinalityUpdate handles received finality update; either validates it if
+// the chain is properly synced or stores it for further validation.
 func (s *HeadSync) newFinalityUpdate(server request.Server, finalityUpdate types.FinalityUpdate) {
 	if !s.chainInit || types.SyncPeriod(finalityUpdate.SignatureSlot) > s.nextSyncPeriod {
 		s.unvalidatedFinality[server] = finalityUpdate
 		return
 	}
-	s.headTracker.ValidateFinality(finalityUpdate)
+	if _, err := s.headTracker.ValidateFinality(finalityUpdate); err != nil {
+		log.Debug("Error validating finality update", "error", err)
+	}
 }
 
-// processUnvalidated iterates the list of unvalidated heads and validates
+// processUnvalidatedUpdates iterates the list of unvalidated updates and validates
 // those which can be validated.
-func (s *HeadSync) processUnvalidated() {
+func (s *HeadSync) processUnvalidatedUpdates() {
 	if !s.chainInit {
 		return
 	}
-	for server, signedHead := range s.unvalidatedHeads {
-		if types.SyncPeriod(signedHead.SignatureSlot) <= s.nextSyncPeriod {
-			s.headTracker.ValidateHead(signedHead)
-			delete(s.unvalidatedHeads, server)
+	for server, optimisticUpdate := range s.unvalidatedOptimistic {
+		if types.SyncPeriod(optimisticUpdate.SignatureSlot) <= s.nextSyncPeriod {
+			if _, err := s.headTracker.ValidateOptimistic(optimisticUpdate); err != nil {
+				log.Debug("Error validating deferred optimistic update", "error", err)
+			}
+			delete(s.unvalidatedOptimistic, server)
 		}
 	}
 	for server, finalityUpdate := range s.unvalidatedFinality {
 		if types.SyncPeriod(finalityUpdate.SignatureSlot) <= s.nextSyncPeriod {
-			s.headTracker.ValidateFinality(finalityUpdate)
+			if _, err := s.headTracker.ValidateFinality(finalityUpdate); err != nil {
+				log.Debug("Error validating deferred finality update", "error", err)
+			}
 			delete(s.unvalidatedFinality, server)
 		}
 	}
diff --git a/beacon/light/sync/head_sync_test.go b/beacon/light/sync/head_sync_test.go
index a2870b2732..cd7dacf7fe 100644
--- a/beacon/light/sync/head_sync_test.go
+++ b/beacon/light/sync/head_sync_test.go
@@ -19,6 +19,7 @@ package sync
 import (
 	"testing"
 
+	"github.com/ethereum/go-ethereum/beacon/light/request"
 	"github.com/ethereum/go-ethereum/beacon/types"
 	"github.com/ethereum/go-ethereum/common"
 )
@@ -28,6 +29,7 @@ var (
 	testServer2 = testServer("testServer2")
 	testServer3 = testServer("testServer3")
 	testServer4 = testServer("testServer4")
+	testServer5 = testServer("testServer5")
 
 	testHead0 = types.HeadInfo{}
 	testHead1 = types.HeadInfo{Slot: 123, BlockRoot: common.Hash{1}}
@@ -35,13 +37,21 @@ var (
 	testHead3 = types.HeadInfo{Slot: 124, BlockRoot: common.Hash{3}}
 	testHead4 = types.HeadInfo{Slot: 125, BlockRoot: common.Hash{4}}
 
-	testSHead1 = types.SignedHeader{SignatureSlot: 0x0124, Header: types.Header{Slot: 0x0123, StateRoot: common.Hash{1}}}
-	testSHead2 = types.SignedHeader{SignatureSlot: 0x2010, Header: types.Header{Slot: 0x200e, StateRoot: common.Hash{2}}}
-	// testSHead3 is at the end of period 1 but signed in period 2
-	testSHead3 = types.SignedHeader{SignatureSlot: 0x4000, Header: types.Header{Slot: 0x3fff, StateRoot: common.Hash{3}}}
-	testSHead4 = types.SignedHeader{SignatureSlot: 0x6444, Header: types.Header{Slot: 0x6443, StateRoot: common.Hash{4}}}
+	testOptUpdate1 = types.OptimisticUpdate{SignatureSlot: 0x0124, Attested: types.HeaderWithExecProof{Header: types.Header{Slot: 0x0123, StateRoot: common.Hash{1}}}}
+	testOptUpdate2 = types.OptimisticUpdate{SignatureSlot: 0x2010, Attested: types.HeaderWithExecProof{Header: types.Header{Slot: 0x200e, StateRoot: common.Hash{2}}}}
+	// testOptUpdate3 is at the end of period 1 but signed in period 2
+	testOptUpdate3 = types.OptimisticUpdate{SignatureSlot: 0x4000, Attested: types.HeaderWithExecProof{Header: types.Header{Slot: 0x3fff, StateRoot: common.Hash{3}}}}
+	testOptUpdate4 = types.OptimisticUpdate{SignatureSlot: 0x6444, Attested: types.HeaderWithExecProof{Header: types.Header{Slot: 0x6443, StateRoot: common.Hash{4}}}}
 )
 
+func finality(opt types.OptimisticUpdate) types.FinalityUpdate {
+	return types.FinalityUpdate{
+		SignatureSlot: opt.SignatureSlot,
+		Attested:      opt.Attested,
+		Finalized:     types.HeaderWithExecProof{Header: types.Header{Slot: (opt.Attested.Header.Slot - 64) & uint64(0xffffffffffffffe0)}},
+	}
+}
+
 type testServer string
 
 func (t testServer) Name() string {
@@ -57,50 +67,66 @@ func TestValidatedHead(t *testing.T) {
 	ht.ExpValidated(t, 0, nil)
 
 	ts.AddServer(testServer1, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead1)
-	ts.Run(1)
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer1, testOptUpdate1)
+	ts.Run(1, testServer1, ReqFinality{})
 	// announced head should be queued because of uninitialized chain
 	ht.ExpValidated(t, 1, nil)
 
 	chain.SetNextSyncPeriod(0) // initialize chain
 	ts.Run(2)
 	// expect previously queued head to be validated
-	ht.ExpValidated(t, 2, []types.SignedHeader{testSHead1})
+	ht.ExpValidated(t, 2, []types.OptimisticUpdate{testOptUpdate1})
 
 	chain.SetNextSyncPeriod(1)
-	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead2)
+	ts.ServerEvent(EvNewFinalityUpdate, testServer1, finality(testOptUpdate2))
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer1, testOptUpdate2)
 	ts.AddServer(testServer2, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer2, testSHead2)
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer2, testOptUpdate2)
 	ts.Run(3)
 	// expect both head announcements to be validated instantly
-	ht.ExpValidated(t, 3, []types.SignedHeader{testSHead2, testSHead2})
+	ht.ExpValidated(t, 3, []types.OptimisticUpdate{testOptUpdate2, testOptUpdate2})
 
-	ts.ServerEvent(EvNewSignedHead, testServer1, testSHead3)
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer1, testOptUpdate3)
 	ts.AddServer(testServer3, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer3, testSHead4)
-	ts.Run(4)
-	// future period announced heads should be queued
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer3, testOptUpdate4)
+	// finality should be requested from both servers
+	ts.Run(4, testServer1, ReqFinality{}, testServer3, ReqFinality{})
+	// future period annonced heads should be queued
 	ht.ExpValidated(t, 4, nil)
 
 	chain.SetNextSyncPeriod(2)
 	ts.Run(5)
-	// testSHead3 can be validated now but not testSHead4
-	ht.ExpValidated(t, 5, []types.SignedHeader{testSHead3})
+	// testOptUpdate3 can be validated now but not testOptUpdate4
+	ht.ExpValidated(t, 5, []types.OptimisticUpdate{testOptUpdate3})
+
+	ts.AddServer(testServer4, 1)
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer4, testOptUpdate3)
+	// new server joined with recent optimistic update but still no finality; should be requested
+	ts.Run(6, testServer4, ReqFinality{})
+	ht.ExpValidated(t, 6, []types.OptimisticUpdate{testOptUpdate3})
+
+	ts.AddServer(testServer5, 1)
+	ts.RequestEvent(request.EvResponse, ts.Request(6, 1), finality(testOptUpdate3))
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer5, testOptUpdate3)
+	// finality update request answered; new server should not be requested
+	ts.Run(7)
+	ht.ExpValidated(t, 7, []types.OptimisticUpdate{testOptUpdate3})
 
 	// server 3 disconnected without proving period 3, its announced head should be dropped
 	ts.RemoveServer(testServer3)
-	ts.Run(6)
-	ht.ExpValidated(t, 6, nil)
+	ts.Run(8)
+	ht.ExpValidated(t, 8, nil)
 
 	chain.SetNextSyncPeriod(3)
-	ts.Run(7)
-	// testSHead4 could be validated now but it's not queued by any registered server
-	ht.ExpValidated(t, 7, nil)
+	ts.Run(9)
+	// testOptUpdate4 could be validated now but it's not queued by any registered server
+	ht.ExpValidated(t, 9, nil)
 
-	ts.ServerEvent(EvNewSignedHead, testServer2, testSHead4)
-	ts.Run(8)
-	// now testSHead4 should be validated
-	ht.ExpValidated(t, 8, []types.SignedHeader{testSHead4})
+	ts.ServerEvent(EvNewFinalityUpdate, testServer2, finality(testOptUpdate4))
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer2, testOptUpdate4)
+	ts.Run(10)
+	// now testOptUpdate4 should be validated
+	ht.ExpValidated(t, 10, []types.OptimisticUpdate{testOptUpdate4})
 }
 
 func TestPrefetchHead(t *testing.T) {
diff --git a/beacon/light/sync/test_helpers.go b/beacon/light/sync/test_helpers.go
index 9f57ceebe4..cfca8ad8a4 100644
--- a/beacon/light/sync/test_helpers.go
+++ b/beacon/light/sync/test_helpers.go
@@ -212,32 +212,37 @@ func (tc *TestCommitteeChain) ExpNextSyncPeriod(t *testing.T, expNsp uint64) {
 
 type TestHeadTracker struct {
 	phead     types.HeadInfo
-	validated []types.SignedHeader
+	validated []types.OptimisticUpdate
+	finality  types.FinalityUpdate
 }
 
-func (ht *TestHeadTracker) ValidateHead(head types.SignedHeader) (bool, error) {
-	ht.validated = append(ht.validated, head)
+func (ht *TestHeadTracker) ValidateOptimistic(update types.OptimisticUpdate) (bool, error) {
+	ht.validated = append(ht.validated, update)
 	return true, nil
 }
 
-// TODO add test case for finality
-func (ht *TestHeadTracker) ValidateFinality(head types.FinalityUpdate) (bool, error) {
+func (ht *TestHeadTracker) ValidateFinality(update types.FinalityUpdate) (bool, error) {
+	ht.finality = update
 	return true, nil
 }
 
-func (ht *TestHeadTracker) ExpValidated(t *testing.T, tci int, expHeads []types.SignedHeader) {
+func (ht *TestHeadTracker) ValidatedFinality() (types.FinalityUpdate, bool) {
+	return ht.finality, ht.finality.Attested.Header != (types.Header{})
+}
+
+func (ht *TestHeadTracker) ExpValidated(t *testing.T, tci int, expHeads []types.OptimisticUpdate) {
 	for i, expHead := range expHeads {
 		if i >= len(ht.validated) {
-			t.Errorf("Missing validated head in test case #%d index #%d (expected {slot %d blockRoot %x}, got none)", tci, i, expHead.Header.Slot, expHead.Header.Hash())
+			t.Errorf("Missing validated head in test case #%d index #%d (expected {slot %d blockRoot %x}, got none)", tci, i, expHead.Attested.Header.Slot, expHead.Attested.Header.Hash())
 			continue
 		}
-		if ht.validated[i] != expHead {
-			vhead := ht.validated[i].Header
-			t.Errorf("Wrong validated head in test case #%d index #%d (expected {slot %d blockRoot %x}, got {slot %d blockRoot %x})", tci, i, expHead.Header.Slot, expHead.Header.Hash(), vhead.Slot, vhead.Hash())
+		if !reflect.DeepEqual(ht.validated[i], expHead) {
+			vhead := ht.validated[i].Attested.Header
+			t.Errorf("Wrong validated head in test case #%d index #%d (expected {slot %d blockRoot %x}, got {slot %d blockRoot %x})", tci, i, expHead.Attested.Header.Slot, expHead.Attested.Header.Hash(), vhead.Slot, vhead.Hash())
 		}
 	}
 	for i := len(expHeads); i < len(ht.validated); i++ {
-		vhead := ht.validated[i].Header
+		vhead := ht.validated[i].Attested.Header
 		t.Errorf("Unexpected validated head in test case #%d index #%d (expected none, got {slot %d blockRoot %x})", tci, i, vhead.Slot, vhead.Hash())
 	}
 	ht.validated = nil
diff --git a/beacon/light/sync/types.go b/beacon/light/sync/types.go
index 8aa4c95f46..97a3fb2111 100644
--- a/beacon/light/sync/types.go
+++ b/beacon/light/sync/types.go
@@ -23,9 +23,9 @@ import (
 )
 
 var (
-	EvNewHead           = &request.EventType{Name: "newHead"}           // data: types.HeadInfo
-	EvNewSignedHead     = &request.EventType{Name: "newSignedHead"}     // data: types.SignedHeader
-	EvNewFinalityUpdate = &request.EventType{Name: "newFinalityUpdate"} // data: types.FinalityUpdate
+	EvNewHead             = &request.EventType{Name: "newHead"}             // data: types.HeadInfo
+	EvNewOptimisticUpdate = &request.EventType{Name: "newOptimisticUpdate"} // data: types.OptimisticUpdate
+	EvNewFinalityUpdate   = &request.EventType{Name: "newFinalityUpdate"}   // data: types.FinalityUpdate
 )
 
 type (
@@ -43,4 +43,5 @@ type (
 	}
 	ReqCheckpointData common.Hash
 	ReqBeaconBlock    common.Hash
+	ReqFinality       struct{}
 )
diff --git a/beacon/light/sync/update_sync.go b/beacon/light/sync/update_sync.go
index 71801b1b60..9549ee5992 100644
--- a/beacon/light/sync/update_sync.go
+++ b/beacon/light/sync/update_sync.go
@@ -84,6 +84,7 @@ func (s *CheckpointInit) Process(requester request.Requester, events []request.E
 	if s.initialized {
 		return
 	}
+
 	for _, event := range events {
 		switch event.Type {
 		case request.EvResponse, request.EvFail, request.EvTimeout:
@@ -132,10 +133,12 @@ func (s *CheckpointInit) Process(requester request.Requester, events []request.E
 				newState.state = ssPrintStatus
 				s.serverState[sid.Server] = newState
 			}
+
 		case request.EvUnregistered:
 			delete(s.serverState, event.Server)
 		}
 	}
+
 	// start a request if possible
 	for _, server := range requester.CanSendTo() {
 		switch s.serverState[server].state {
@@ -156,6 +159,7 @@ func (s *CheckpointInit) Process(requester request.Requester, events []request.E
 			s.serverState[server] = newState
 		}
 	}
+
 	// print log message if necessary
 	for server, state := range s.serverState {
 		if state.state != ssPrintStatus {
@@ -316,9 +320,9 @@ func (s *ForwardUpdateSync) Process(requester request.Requester, events []reques
 			if !queued {
 				s.unlockRange(sid, req)
 			}
-		case EvNewSignedHead:
-			signedHead := event.Data.(types.SignedHeader)
-			s.nextSyncPeriod[event.Server] = types.SyncPeriod(signedHead.SignatureSlot + 256)
+		case EvNewOptimisticUpdate:
+			update := event.Data.(types.OptimisticUpdate)
+			s.nextSyncPeriod[event.Server] = types.SyncPeriod(update.SignatureSlot + 256)
 		case request.EvUnregistered:
 			delete(s.nextSyncPeriod, event.Server)
 		}
diff --git a/beacon/light/sync/update_sync_test.go b/beacon/light/sync/update_sync_test.go
index 1c4b3d6d76..8329bf28c9 100644
--- a/beacon/light/sync/update_sync_test.go
+++ b/beacon/light/sync/update_sync_test.go
@@ -68,9 +68,9 @@ func TestUpdateSyncParallel(t *testing.T) {
 	ts := NewTestScheduler(t, updateSync)
 	// add 2 servers, head at period 100; allow 3-3 parallel requests for each
 	ts.AddServer(testServer1, 3)
-	ts.ServerEvent(EvNewSignedHead, testServer1, types.SignedHeader{SignatureSlot: 0x2000*100 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer1, types.OptimisticUpdate{SignatureSlot: 0x2000*100 + 0x1000})
 	ts.AddServer(testServer2, 3)
-	ts.ServerEvent(EvNewSignedHead, testServer2, types.SignedHeader{SignatureSlot: 0x2000*100 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer2, types.OptimisticUpdate{SignatureSlot: 0x2000*100 + 0x1000})
 
 	// expect 6 requests to be sent
 	ts.Run(1,
@@ -150,11 +150,11 @@ func TestUpdateSyncDifferentHeads(t *testing.T) {
 	ts := NewTestScheduler(t, updateSync)
 	// add 3 servers with different announced head periods
 	ts.AddServer(testServer1, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer1, types.SignedHeader{SignatureSlot: 0x2000*15 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer1, types.OptimisticUpdate{SignatureSlot: 0x2000*15 + 0x1000})
 	ts.AddServer(testServer2, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer2, types.SignedHeader{SignatureSlot: 0x2000*16 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer2, types.OptimisticUpdate{SignatureSlot: 0x2000*16 + 0x1000})
 	ts.AddServer(testServer3, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer3, types.SignedHeader{SignatureSlot: 0x2000*17 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer3, types.OptimisticUpdate{SignatureSlot: 0x2000*17 + 0x1000})
 
 	// expect request to the best announced head
 	ts.Run(1, testServer3, ReqUpdates{FirstPeriod: 10, Count: 7})
@@ -190,7 +190,7 @@ func TestUpdateSyncDifferentHeads(t *testing.T) {
 
 	// a new server is registered with announced head period 17
 	ts.AddServer(testServer4, 1)
-	ts.ServerEvent(EvNewSignedHead, testServer4, types.SignedHeader{SignatureSlot: 0x2000*17 + 0x1000})
+	ts.ServerEvent(EvNewOptimisticUpdate, testServer4, types.OptimisticUpdate{SignatureSlot: 0x2000*17 + 0x1000})
 	// expect request to sync one more period
 	ts.Run(7, testServer4, ReqUpdates{FirstPeriod: 16, Count: 1})
 
diff --git a/beacon/types/exec_payload.go b/beacon/types/exec_payload.go
index 604de288d2..718f98f529 100644
--- a/beacon/types/exec_payload.go
+++ b/beacon/types/exec_payload.go
@@ -66,9 +66,8 @@ func convertPayload[T payloadType](payload T, parentRoot *zrntcommon.Root) (*typ
 	block := types.NewBlockWithHeader(&header)
 	block = block.WithBody(transactions, nil)
 	block = block.WithWithdrawals(withdrawals)
-	hash := block.Hash()
-	if hash != expectedHash {
-		return block, fmt.Errorf("Sanity check failed, payload hash does not match (expected %x, got %x)", expectedHash, hash)
+	if hash := block.Hash(); hash != expectedHash {
+		return nil, fmt.Errorf("Sanity check failed, payload hash does not match (expected %x, got %x)", expectedHash, hash)
 	}
 	return block, nil
 }
diff --git a/beacon/types/light_sync.go b/beacon/types/light_sync.go
index 62becdb21c..3e9b13d0e2 100644
--- a/beacon/types/light_sync.go
+++ b/beacon/types/light_sync.go
@@ -23,7 +23,7 @@ import (
 	"github.com/ethereum/go-ethereum/beacon/merkle"
 	"github.com/ethereum/go-ethereum/beacon/params"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/core/types"
+	ctypes "github.com/ethereum/go-ethereum/core/types"
 )
 
 // HeadInfo represents an unvalidated new head announcement.
@@ -142,17 +142,57 @@ func (u UpdateScore) BetterThan(w UpdateScore) bool {
 	return u.SignerCount > w.SignerCount
 }
 
+// HeaderWithExecProof contains a beacon header and proves the belonging execution
+// payload header with a Merkle proof.
 type HeaderWithExecProof struct {
 	Header
 	PayloadHeader *ExecutionHeader
 	PayloadBranch merkle.Values
 }
 
+// Validate verifies the Merkle proof of the execution payload header.
 func (h *HeaderWithExecProof) Validate() error {
-	payloadRoot := h.PayloadHeader.PayloadRoot()
-	return merkle.VerifyProof(h.BodyRoot, params.BodyIndexExecPayload, h.PayloadBranch, payloadRoot)
+	return merkle.VerifyProof(h.BodyRoot, params.BodyIndexExecPayload, h.PayloadBranch, h.PayloadHeader.PayloadRoot())
 }
 
+// OptimisticUpdate proves sync committee commitment on the attested beacon header.
+// It also proves the belonging execution payload header with a Merkle proof.
+//
+// See data structure definition here:
+// https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/light-client/sync-protocol.md#lightclientoptimisticupdate
+type OptimisticUpdate struct {
+	Attested HeaderWithExecProof
+	// Sync committee BLS signature aggregate
+	Signature SyncAggregate
+	// Slot in which the signature has been created (newer than Header.Slot,
+	// determines the signing sync committee)
+	SignatureSlot uint64
+}
+
+// SignedHeader returns the signed attested header of the update.
+func (u *OptimisticUpdate) SignedHeader() SignedHeader {
+	return SignedHeader{
+		Header:        u.Attested.Header,
+		Signature:     u.Signature,
+		SignatureSlot: u.SignatureSlot,
+	}
+}
+
+// Validate verifies the Merkle proof proving the execution payload header.
+// Note that the sync committee signature of the attested header should be
+// verified separately by a synced committee chain.
+func (u *OptimisticUpdate) Validate() error {
+	return u.Attested.Validate()
+}
+
+// FinalityUpdate proves a finalized beacon header by a sync committee commitment
+// on an attested beacon header, referring to the latest finalized header with a
+// Merkle proof.
+// It also proves the execution payload header belonging to both the attested and
+// the finalized beacon header with Merkle proofs.
+//
+// See data structure definition here:
+// https://github.com/ethereum/consensus-specs/blob/dev/specs/altair/light-client/sync-protocol.md#lightclientfinalityupdate
 type FinalityUpdate struct {
 	Attested, Finalized HeaderWithExecProof
 	FinalityBranch      merkle.Values
@@ -163,6 +203,7 @@ type FinalityUpdate struct {
 	SignatureSlot uint64
 }
 
+// SignedHeader returns the signed attested header of the update.
 func (u *FinalityUpdate) SignedHeader() SignedHeader {
 	return SignedHeader{
 		Header:        u.Attested.Header,
@@ -171,6 +212,10 @@ func (u *FinalityUpdate) SignedHeader() SignedHeader {
 	}
 }
 
+// Validate verifies the Merkle proofs proving the finalized beacon header and
+// the execution payload headers belonging to the attested and finalized headers.
+// Note that the sync committee signature of the attested header should be
+// verified separately by a synced committee chain.
 func (u *FinalityUpdate) Validate() error {
 	if err := u.Attested.Validate(); err != nil {
 		return err
@@ -186,6 +231,6 @@ func (u *FinalityUpdate) Validate() error {
 // finalized execution block.
 type ChainHeadEvent struct {
 	BeaconHead Header
-	Block      *types.Block
+	Block      *ctypes.Block
 	Finalized  common.Hash
 }