diff --git a/pkg/api/handler.go b/pkg/api/handler.go
index 319600f3..e51b5a7e 100644
--- a/pkg/api/handler.go
+++ b/pkg/api/handler.go
@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"strconv"
 	"strings"
 	"time"
 
@@ -599,7 +600,21 @@ func (h *Handler) handleEthV1BeaconBlobSidecars(ctx context.Context, r *http.Req
 		return NewBadRequestResponse(nil), err
 	}
 
-	sidecars, err := h.eth.BlobSidecars(ctx, id)
+	queryParams := r.URL.Query()
+	indicesRaw := queryParams["indices"]
+
+	indices := make([]int, 0, len(indicesRaw))
+
+	for _, index := range indicesRaw {
+		converted, errr := strconv.Atoi(index)
+		if errr != nil {
+			return NewBadRequestResponse(nil), errr
+		}
+
+		indices = append(indices, converted)
+	}
+
+	sidecars, err := h.eth.BlobSidecars(ctx, id, indices)
 	if err != nil {
 		return NewInternalServerErrorResponse(nil), err
 	}
diff --git a/pkg/beacon/default.go b/pkg/beacon/default.go
index a201c8ed..345a3c65 100644
--- a/pkg/beacon/default.go
+++ b/pkg/beacon/default.go
@@ -41,8 +41,9 @@ type Default struct {
 	depositSnapshots *store.DepositSnapshot
 	blobSidecars     *store.BlobSidecar
 
-	spec    *state.Spec
-	genesis *v1.Genesis
+	specMutex sync.Mutex
+	spec      *state.Spec
+	genesis   *v1.Genesis
 
 	historicalSlotFailures map[phase0.Slot]int
 
@@ -86,6 +87,7 @@ func NewDefaultProvider(namespace string, log logrus.FieldLogger, nodes []node.C
 		servingMutex:    sync.Mutex{},
 		historicalMutex: sync.Mutex{},
 		majorityMutex:   sync.Mutex{},
+		specMutex:       sync.Mutex{},
 
 		metrics: NewMetrics(namespace + "_beacon"),
 	}
@@ -103,7 +105,7 @@ func (d *Default) Start(ctx context.Context) error {
 	go func() {
 		for {
 			// Wait until we have a single healthy node.
-			_, err := d.nodes.Healthy(ctx).NotSyncing(ctx).RandomNode(ctx)
+			nd, err := d.nodes.Healthy(ctx).NotSyncing(ctx).RandomNode(ctx)
 			if err != nil {
 				d.log.WithError(err).Error("Waiting for a healthy, non-syncing node before beginning..")
 				time.Sleep(time.Second * 5)
@@ -111,10 +113,28 @@ func (d *Default) Start(ctx context.Context) error {
 				continue
 			}
 
+			nd.Beacon.Wallclock().OnEpochChanged(func(epoch ethwallclock.Epoch) {
+				// Refresh the spec on epoch change.
+				// This will intentionally use any node (not the one that triggered the event) to fetch the spec.
+				if err := d.refreshSpec(ctx); err != nil {
+					d.log.WithError(err).Error("Failed to refresh spec")
+				}
+			})
+
 			if err := d.startCrons(ctx); err != nil {
 				d.log.WithError(err).Fatal("Failed to start crons")
 			}
 
+			go func() {
+				if err := d.startGenesisLoop(ctx); err != nil {
+					d.log.WithError(err).Fatal("Failed to start genesis loop")
+				}
+			}()
+
+			if err := d.fetchUpstreamRequirements(ctx); err != nil {
+				d.log.WithError(err).Error("Failed to fetch upstream requirements")
+			}
+
 			break
 		}
 	}()
@@ -124,7 +144,8 @@ func (d *Default) Start(ctx context.Context) error {
 		n := node
 
 		logCtx := d.log.WithFields(logrus.Fields{
-			"node": n.Config.Name,
+			"node":   n.Config.Name,
+			"reason": "serving_updater",
 		})
 
 		n.Beacon.OnFinalityCheckpointUpdated(ctx, func(ctx context.Context, event *beacon.FinalityCheckpointUpdated) error {
@@ -140,7 +161,13 @@ func (d *Default) Start(ctx context.Context) error {
 				return err
 			}
 
-			return d.checkForNewServingCheckpoint(ctx)
+			if err := d.checkForNewServingCheckpoint(ctx); err != nil {
+				logCtx.WithError(err).Error("Failed to check for new serving checkpoint after finality checkpoint updated")
+
+				return err
+			}
+
+			return nil
 		})
 
 		n.Beacon.OnReady(ctx, func(ctx context.Context, _ *beacon.ReadyEvent) error {
@@ -196,12 +223,6 @@ func (d *Default) startCrons(ctx context.Context) error {
 		return err
 	}
 
-	go func() {
-		if err := d.startGenesisLoop(ctx); err != nil {
-			d.log.WithError(err).Fatal("Failed to start genesis loop")
-		}
-	}()
-
 	go func() {
 		if err := d.startServingLoop(ctx); err != nil {
 			d.log.WithError(err).Fatal("Failed to start serving loop")
@@ -219,6 +240,14 @@ func (d *Default) startCrons(ctx context.Context) error {
 	return nil
 }
 
+func (d *Default) fetchUpstreamRequirements(ctx context.Context) error {
+	if err := d.refreshSpec(ctx); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func (d *Default) StartAsync(ctx context.Context) {
 	go func() {
 		if err := d.Start(ctx); err != nil {
@@ -369,7 +398,7 @@ func (d *Default) Syncing(ctx context.Context) (*v1.SyncState, error) {
 		SyncDistance: 0,
 	}
 
-	sp, err := d.Spec(ctx)
+	sp, err := d.Spec()
 	if err != nil {
 		return syncState, err
 	}
@@ -405,12 +434,24 @@ func (d *Default) Genesis(ctx context.Context) (*v1.Genesis, error) {
 	return d.genesis, nil
 }
 
-func (d *Default) Spec(ctx context.Context) (*state.Spec, error) {
+func (d *Default) setSpec(s *state.Spec) {
+	d.specMutex.Lock()
+	defer d.specMutex.Unlock()
+
+	d.spec = s
+}
+
+func (d *Default) Spec() (*state.Spec, error) {
+	d.specMutex.Lock()
+	defer d.specMutex.Unlock()
+
 	if d.spec == nil {
 		return nil, errors.New("config spec not yet available")
 	}
 
-	return d.spec, nil
+	copied := *d.spec
+
+	return &copied, nil
 }
 
 func (d *Default) OperatingMode() OperatingMode {
@@ -460,12 +501,7 @@ func (d *Default) checkFinality(ctx context.Context) error {
 	return nil
 }
 
-func (d *Default) checkBeaconSpec(ctx context.Context) error {
-	// No-Op if we already have a beacon spec
-	if d.spec != nil {
-		return nil
-	}
-
+func (d *Default) refreshSpec(ctx context.Context) error {
 	d.log.Debug("Fetching beacon spec")
 
 	upstream, err := d.nodes.Ready(ctx).DataProviders(ctx).RandomNode(ctx)
@@ -479,13 +515,23 @@ func (d *Default) checkBeaconSpec(ctx context.Context) error {
 	}
 
 	// store the beacon state spec
-	d.spec = s
+	d.setSpec(s)
 
-	d.log.Info("Fetched beacon spec")
+	d.log.Debug("Fetched beacon spec")
 
 	return nil
 }
 
+func (d *Default) checkBeaconSpec(ctx context.Context) error {
+	// No-Op if we already have a beacon spec
+	_, err := d.Spec()
+	if err == nil {
+		return nil
+	}
+
+	return d.refreshSpec(ctx)
+}
+
 func (d *Default) checkGenesisTime(ctx context.Context) error {
 	// No-Op if we already have a genesis time
 	if d.genesis != nil {
@@ -520,7 +566,7 @@ func (d *Default) OnFinalityCheckpointHeadUpdated(ctx context.Context, cb func(c
 	})
 }
 
-func (d *Default) publishFinalityCheckpointHeadUpdated(ctx context.Context, checkpoint *v1.Finality) {
+func (d *Default) publishFinalityCheckpointHeadUpdated(_ context.Context, checkpoint *v1.Finality) {
 	d.broker.Emit(topicFinalityHeadUpdated, checkpoint)
 }
 
@@ -599,9 +645,10 @@ func (d *Default) GetBeaconStateByRoot(ctx context.Context, root phase0.Root) (*
 	return d.states.GetByStateRoot(stateRoot)
 }
 
-func (d *Default) storeBlock(ctx context.Context, block *spec.VersionedSignedBeaconBlock) error {
-	if d.spec == nil {
-		return errors.New("beacon chain spec is unknown")
+func (d *Default) storeBlock(_ context.Context, block *spec.VersionedSignedBeaconBlock) error {
+	_, err := d.Spec()
+	if err != nil {
+		return err
 	}
 
 	if d.genesis == nil {
@@ -679,7 +726,9 @@ func (d *Default) UpstreamsStatus(ctx context.Context) (map[string]*UpstreamStat
 
 func (d *Default) ListFinalizedSlots(ctx context.Context) ([]phase0.Slot, error) {
 	slots := []phase0.Slot{}
-	if d.spec == nil {
+
+	sp, err := d.Spec()
+	if err != nil {
 		return slots, errors.New("no beacon chain spec available")
 	}
 
@@ -692,9 +741,9 @@ func (d *Default) ListFinalizedSlots(ctx context.Context) ([]phase0.Slot, error)
 		return slots, errors.New("no finalized checkpoint available")
 	}
 
-	latestSlot := phase0.Slot(uint64(finality.Finalized.Epoch) * uint64(d.spec.SlotsPerEpoch))
+	latestSlot := phase0.Slot(uint64(finality.Finalized.Epoch) * uint64(sp.SlotsPerEpoch))
 
-	for i, val := uint64(latestSlot), uint64(latestSlot)-uint64(d.spec.SlotsPerEpoch)*uint64(d.config.HistoricalEpochCount); i > val; i -= uint64(d.spec.SlotsPerEpoch) {
+	for i, val := uint64(latestSlot), uint64(latestSlot)-uint64(sp.SlotsPerEpoch)*uint64(d.config.HistoricalEpochCount); i > val; i -= uint64(sp.SlotsPerEpoch) {
 		slots = append(slots, phase0.Slot(i))
 	}
 
@@ -702,7 +751,8 @@ func (d *Default) ListFinalizedSlots(ctx context.Context) ([]phase0.Slot, error)
 }
 
 func (d *Default) GetEpochBySlot(ctx context.Context, slot phase0.Slot) (phase0.Epoch, error) {
-	if d.spec == nil {
+	_, err := d.Spec()
+	if err != nil {
 		return phase0.Epoch(0), errors.New("no upstream beacon state spec available")
 	}
 
@@ -716,7 +766,8 @@ func (d *Default) PeerCount(ctx context.Context) (uint64, error) {
 func (d *Default) GetSlotTime(ctx context.Context, slot phase0.Slot) (eth.SlotTime, error) {
 	SlotTime := eth.SlotTime{}
 
-	if d.spec == nil {
+	_, err := d.Spec()
+	if err != nil {
 		return SlotTime, errors.New("no upstream beacon state spec available")
 	}
 
diff --git a/pkg/beacon/download.go b/pkg/beacon/download.go
index 7074c020..11bc24d7 100644
--- a/pkg/beacon/download.go
+++ b/pkg/beacon/download.go
@@ -23,6 +23,8 @@ func (d *Default) downloadServingCheckpoint(ctx context.Context, checkpoint *v1.
 		return errors.New("finalized checkpoint is nil")
 	}
 
+	d.log.WithField("epoch", checkpoint.Finalized.Epoch).Info("Downloading serving checkpoint")
+
 	upstream, err := d.nodes.
 		Ready(ctx).
 		DataProviders(ctx).
@@ -44,10 +46,12 @@ func (d *Default) downloadServingCheckpoint(ctx context.Context, checkpoint *v1.
 		return fmt.Errorf("failed to get slot from block: %w", err)
 	}
 
-	// For simplicity we'll hardcode SLOTS_PER_EPOCH to 32.
-	// TODO(sam.calder-mason): Fetch this from a beacon node and store it in the instance.
-	const slotsPerEpoch = 32
-	if blockSlot%slotsPerEpoch != 0 {
+	sp, err := d.Spec()
+	if err != nil {
+		return fmt.Errorf("failed to fetch spec: %w", err)
+	}
+
+	if blockSlot%sp.SlotsPerEpoch != 0 {
 		return fmt.Errorf("block slot is not aligned from an epoch boundary: %d", blockSlot)
 	}
 
@@ -129,8 +133,9 @@ func (d *Default) fetchHistoricalCheckpoints(ctx context.Context, checkpoint *v1
 	d.historicalMutex.Lock()
 	defer d.historicalMutex.Unlock()
 
-	if d.spec == nil {
-		return errors.New("beacon spec unavailable")
+	sp, err := d.Spec()
+	if err != nil {
+		return errors.New("chain spec unavailable")
 	}
 
 	if d.genesis == nil {
@@ -147,8 +152,6 @@ func (d *Default) fetchHistoricalCheckpoints(ctx context.Context, checkpoint *v1
 		return errors.New("no data provider node available")
 	}
 
-	sp := d.spec
-
 	slotsInScope := make(map[phase0.Slot]struct{})
 
 	// We always care about the genesis slot.
@@ -218,7 +221,8 @@ func (d *Default) downloadBlock(ctx context.Context, slot phase0.Slot, upstream
 	}
 
 	// Same thing with the chain spec.
-	if d.spec == nil {
+	_, err := d.Spec()
+	if err != nil {
 		return nil, errors.New("chain spec not known")
 	}
 
@@ -326,9 +330,9 @@ func (d *Default) fetchBundle(ctx context.Context, root phase0.Root, upstream *N
 		}
 	}
 
-	sp, err := upstream.Beacon.Spec()
+	sp, err := d.Spec()
 	if err != nil {
-		return nil, fmt.Errorf("failed to fetch spec from upstream node: %w", err)
+		return nil, fmt.Errorf("failed to fetch spec: %w", err)
 	}
 
 	denebFork, err := sp.ForkEpochs.GetByName("DENEB")
@@ -341,7 +345,7 @@ func (d *Default) fetchBundle(ctx context.Context, root phase0.Root, upstream *N
 		}
 	}
 
-	d.log.Infof("Successfully fetched bundle from %s", upstream.Config.Name)
+	d.log.WithField("root", eth.RootAsString(root)).Infof("Successfully fetched bundle from %s", upstream.Config.Name)
 
 	return block, nil
 }
diff --git a/pkg/beacon/finality_provider.go b/pkg/beacon/finality_provider.go
index f3eb0c88..108e3bab 100644
--- a/pkg/beacon/finality_provider.go
+++ b/pkg/beacon/finality_provider.go
@@ -33,7 +33,7 @@ type FinalityProvider interface {
 	// Genesis returns the chain genesis.
 	Genesis(ctx context.Context) (*v1.Genesis, error)
 	// Spec returns the chain spec.
-	Spec(ctx context.Context) (*state.Spec, error)
+	Spec() (*state.Spec, error)
 	// UpstreamsStatus returns the status of all the upstreams.
 	UpstreamsStatus(ctx context.Context) (map[string]*UpstreamStatus, error)
 	// GetBlockBySlot returns the block at the given slot.
diff --git a/pkg/service/eth/eth.go b/pkg/service/eth/eth.go
index 113f7c78..a09c24f8 100644
--- a/pkg/service/eth/eth.go
+++ b/pkg/service/eth/eth.go
@@ -112,7 +112,7 @@ func (h *Handler) ConfigSpec(ctx context.Context) (*state.Spec, error) {
 		}
 	}()
 
-	return h.provider.Spec(ctx)
+	return h.provider.Spec()
 }
 
 // ForkSchedule returns the upcoming forks.
@@ -129,7 +129,7 @@ func (h *Handler) ForkSchedule(ctx context.Context) ([]*state.ScheduledFork, err
 		}
 	}()
 
-	sp, err := h.provider.Spec(ctx)
+	sp, err := h.provider.Spec()
 	if err != nil {
 		return nil, err
 	}
@@ -156,7 +156,7 @@ func (h *Handler) DepositContract(ctx context.Context) (*DepositContract, error)
 		}
 	}()
 
-	sp, err := h.provider.Spec(ctx)
+	sp, err := h.provider.Spec()
 	if err != nil {
 		return nil, err
 	}
@@ -186,6 +186,10 @@ func (h *Handler) DepositSnapshot(ctx context.Context) (*types.DepositSnapshot,
 		return nil, err
 	}
 
+	if finality == nil || finality.Finalized == nil {
+		return nil, fmt.Errorf("no finality known")
+	}
+
 	snapshot, err := h.provider.GetDepositSnapshot(ctx, finality.Finalized.Epoch)
 	if err != nil {
 		return nil, err
@@ -435,7 +439,7 @@ func (h *Handler) BlockRoot(ctx context.Context, blockID BlockIdentifier) (phase
 }
 
 // BlobSidecars returns the blob sidecars for the given block ID.
-func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]*deneb.BlobSidecar, error) {
+func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier, indices []int) ([]*deneb.BlobSidecar, error) {
 	var err error
 
 	const call = "blob_sidecars"
@@ -452,6 +456,7 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]
 
 	switch blockID.Type() {
 	case BlockIDGenesis:
+		//nolint:govet // False positive
 		block, err := h.provider.GetBlockBySlot(ctx, phase0.Slot(0))
 		if err != nil {
 			return nil, err
@@ -468,6 +473,7 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]
 
 		slot = sl
 	case BlockIDSlot:
+		//nolint:govet // False positive
 		sslot, err := NewSlotFromString(blockID.Value())
 		if err != nil {
 			return nil, err
@@ -489,6 +495,7 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]
 
 		slot = sl
 	case BlockIDRoot:
+		//nolint:govet // False positive
 		root, err := blockID.AsRoot()
 		if err != nil {
 			return nil, err
@@ -510,6 +517,7 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]
 
 		slot = sl
 	case BlockIDFinalized:
+		//nolint:govet // False positive
 		finality, err := h.provider.Finalized(ctx)
 		if err != nil {
 			return nil, err
@@ -538,5 +546,31 @@ func (h *Handler) BlobSidecars(ctx context.Context, blockID BlockIdentifier) ([]
 		return nil, fmt.Errorf("invalid block id: %v", blockID.String())
 	}
 
-	return h.provider.GetBlobSidecarsBySlot(ctx, slot)
+	sidecars, err := h.provider.GetBlobSidecarsBySlot(ctx, slot)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(indices) == 0 {
+		return sidecars, nil
+	}
+
+	filtered := make([]*deneb.BlobSidecar, 0, len(indices))
+
+	for _, index := range indices {
+		if index < 0 {
+			return nil, fmt.Errorf("invalid index %v", index)
+		}
+
+		// Find the sidecar with the given index
+		for i, sidecar := range sidecars {
+			if index == int(sidecar.Index) {
+				filtered = append(filtered, sidecars[i])
+
+				break
+			}
+		}
+	}
+
+	return filtered, nil
 }