diff --git a/go.mod b/go.mod
index 8a8bad8b..c0e9a6cc 100644
--- a/go.mod
+++ b/go.mod
@@ -4,7 +4,7 @@ go 1.21
 
 require (
 	dario.cat/mergo v1.0.0
-	github.com/attestantio/go-eth2-client v0.21.3
+	github.com/attestantio/go-eth2-client v0.0.0-20240507092336-27309754c54f
 	github.com/aws/aws-sdk-go-v2 v1.26.1
 	github.com/aws/aws-sdk-go-v2/config v1.27.11
 	github.com/aws/aws-sdk-go-v2/credentials v1.17.11
@@ -21,6 +21,7 @@ require (
 	github.com/lib/pq v1.10.9
 	github.com/mattn/go-sqlite3 v1.14.22
 	github.com/mitchellh/mapstructure v1.5.0
+	github.com/pk910/dynamic-ssz v0.0.3
 	github.com/pressly/goose/v3 v3.20.0
 	github.com/protolambda/bls12-381-util v0.1.0
 	github.com/protolambda/zrnt v0.32.3
@@ -116,6 +117,7 @@ require (
 	golang.org/x/tools v0.20.0 // indirect
 	golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028 // indirect
 	google.golang.org/protobuf v1.33.0 // indirect
+	gopkg.in/Knetic/govaluate.v3 v3.0.0 // indirect
 	gopkg.in/cenkalti/backoff.v1 v1.1.0 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 	rsc.io/tmplfunc v0.0.3 // indirect
diff --git a/go.sum b/go.sum
index 296154e1..2626297d 100644
--- a/go.sum
+++ b/go.sum
@@ -13,8 +13,8 @@ github.com/StackExchange/wmi v1.2.1 h1:VIkavFPXSjcnS+O8yTq7NI32k0R5Aj+v39y29VYDO
 github.com/StackExchange/wmi v1.2.1/go.mod h1:rcmrprowKIVzvc+NUiLncP2uuArMWLCbu9SBzvHz7e8=
 github.com/VictoriaMetrics/fastcache v1.12.1 h1:i0mICQuojGDL3KblA7wUNlY5lOK6a4bwt3uRKnkZU40=
 github.com/VictoriaMetrics/fastcache v1.12.1/go.mod h1:tX04vaqcNoQeGLD+ra5pU5sWkuxnzWhEzLwhP9w653o=
-github.com/attestantio/go-eth2-client v0.21.3 h1:m4Tzgb5AZkcjvtpmeZSiFireIhdZVK/fSAntJKAH8qM=
-github.com/attestantio/go-eth2-client v0.21.3/go.mod h1:vhb0ZoQ6bz0kkoyxVbHDRrZTOJbwlY6udFkwfwrJZTE=
+github.com/attestantio/go-eth2-client v0.0.0-20240507092336-27309754c54f h1:k4axih4fc/7Atb9eTsPsPFxlGGb501o+ryUt9q0stR8=
+github.com/attestantio/go-eth2-client v0.0.0-20240507092336-27309754c54f/go.mod h1:Ht9tN0WlhpgIWWO7Hqfi3/nq2rUGQv/zCd/BMI93a84=
 github.com/aws/aws-sdk-go-v2 v1.26.1 h1:5554eUqIYVWpU0YmeeYZ0wU64H2VLBs8TlhRB2L+EkA=
 github.com/aws/aws-sdk-go-v2 v1.26.1/go.mod h1:ffIFB97e2yNsv4aTSGkqtHnppsIJzw7G7BReUZ3jCXM=
 github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.6.2 h1:x6xsQXGSmW6frevwDA+vi/wqhp1ct18mVXYN08/93to=
@@ -322,6 +322,10 @@ github.com/onsi/ginkgo v1.16.5 h1:8xi0RTUf59SOSfEtZMvwTvXYMzG4gV23XVHOZiXNtnE=
 github.com/onsi/ginkgo v1.16.5/go.mod h1:+E8gABHa3K6zRBolWtd+ROzc/U5bkGt0FwiG042wbpU=
 github.com/onsi/gomega v1.18.1 h1:M1GfJqGRrBrrGGsbxzV5dqM2U2ApXefZCQpkukxYRLE=
 github.com/onsi/gomega v1.18.1/go.mod h1:0q+aL8jAiMXy9hbwj2mr5GziHiwhAIQpFmmtT5hitRs=
+github.com/pk910/dynamic-ssz v0.0.3 h1:fCWzFowq9P6SYCc7NtJMkZcIHk+r5hSVD+32zVi6Aio=
+github.com/pk910/dynamic-ssz v0.0.3/go.mod h1:b6CrLaB2X7pYA+OSEEbkgXDEcRnjLOZIxZTsMuO/Y9c=
+github.com/pk910/go-eth2-client v0.0.0-20240503111248-b7b883e07eca h1:+SeQtXs6iJyVQX294Ci37a9F5gvlnhIKTj0XvKP1rEQ=
+github.com/pk910/go-eth2-client v0.0.0-20240503111248-b7b883e07eca/go.mod h1:CilNSTpoxAEvYGi5fuWHpj+lN3GC552OtHUops1ctwg=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
@@ -548,6 +552,8 @@ golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028 h1:+cNy6SZtPcJQH3LJVLOSm
 golang.org/x/xerrors v0.0.0-20231012003039-104605ab7028/go.mod h1:NDW/Ps6MPRej6fsCIbMTohpP40sJ/P/vI1MoTEGwX90=
 google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
 google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
+gopkg.in/Knetic/govaluate.v3 v3.0.0 h1:18mUyIt4ZlRlFZAAfVetz4/rzlJs9yhN+U02F4u1AOc=
+gopkg.in/Knetic/govaluate.v3 v3.0.0/go.mod h1:csKLBORsPbafmSCGTEh3U7Ozmsuq8ZSIlKk1bcqph0E=
 gopkg.in/cenkalti/backoff.v1 v1.1.0 h1:Arh75ttbsvlpVA7WtVpH4u9h6Zl46xuptxqLxPiSo4Y=
 gopkg.in/cenkalti/backoff.v1 v1.1.0/go.mod h1:J6Vskwqd+OMVJl8C33mmtxTBs2gyzfv7UDAkHu8BrjI=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
diff --git a/indexer/ssz_helper.go b/indexer/ssz_helper.go
index 7dd25f71..4c787605 100644
--- a/indexer/ssz_helper.go
+++ b/indexer/ssz_helper.go
@@ -10,32 +10,50 @@ import (
 	"github.com/attestantio/go-eth2-client/spec/deneb"
 	"github.com/attestantio/go-eth2-client/spec/phase0"
 	"github.com/ethpandaops/dora/utils"
+	dynssz "github.com/pk910/dynamic-ssz"
+	"gopkg.in/yaml.v3"
 )
 
+var staticConfigSpec map[string]any
 var jsonVersionOffset uint64 = 0x70000000
 
+func getConfigSpec() map[string]any {
+	if staticConfigSpec != nil {
+		return staticConfigSpec
+	}
+
+	staticConfigSpec = map[string]any{}
+	specYaml, err := yaml.Marshal(utils.Config.Chain.Config)
+	if err != nil {
+		yaml.Unmarshal(specYaml, staticConfigSpec)
+	}
+	return staticConfigSpec
+}
+
 func MarshalVersionedSignedBeaconBlockSSZ(block *spec.VersionedSignedBeaconBlock) (version uint64, ssz []byte, err error) {
 	if utils.Config.KillSwitch.DisableSSZEncoding {
 		// SSZ encoding disabled, use json instead
 		return marshalVersionedSignedBeaconBlockJson(block)
 	}
 
+	dynSsz := dynssz.NewDynSsz(getConfigSpec())
+
 	switch block.Version {
 	case spec.DataVersionPhase0:
 		version = uint64(block.Version)
-		ssz, err = block.Phase0.MarshalSSZ()
+		ssz, err = dynSsz.MarshalSSZ(block.Phase0)
 	case spec.DataVersionAltair:
 		version = uint64(block.Version)
-		ssz, err = block.Altair.MarshalSSZ()
+		ssz, err = dynSsz.MarshalSSZ(block.Altair)
 	case spec.DataVersionBellatrix:
 		version = uint64(block.Version)
-		ssz, err = block.Bellatrix.MarshalSSZ()
+		ssz, err = dynSsz.MarshalSSZ(block.Bellatrix)
 	case spec.DataVersionCapella:
 		version = uint64(block.Version)
-		ssz, err = block.Capella.MarshalSSZ()
+		ssz, err = dynSsz.MarshalSSZ(block.Capella)
 	case spec.DataVersionDeneb:
 		version = uint64(block.Version)
-		ssz, err = block.Deneb.MarshalSSZ()
+		ssz, err = dynSsz.MarshalSSZ(block.Deneb)
 	default:
 		err = fmt.Errorf("unknown block version")
 	}
@@ -49,30 +67,32 @@ func UnmarshalVersionedSignedBeaconBlockSSZ(version uint64, ssz []byte) (*spec.V
 	block := &spec.VersionedSignedBeaconBlock{
 		Version: spec.DataVersion(version),
 	}
+	dynSsz := dynssz.NewDynSsz(getConfigSpec())
+
 	switch block.Version {
 	case spec.DataVersionPhase0:
 		block.Phase0 = &phase0.SignedBeaconBlock{}
-		if err := block.Phase0.UnmarshalSSZ(ssz); err != nil {
+		if err := dynSsz.UnmarshalSSZ(block.Phase0, ssz); err != nil {
 			return nil, fmt.Errorf("failed to decode phase0 signed beacon block: %v", err)
 		}
 	case spec.DataVersionAltair:
 		block.Altair = &altair.SignedBeaconBlock{}
-		if err := block.Altair.UnmarshalSSZ(ssz); err != nil {
+		if err := dynSsz.UnmarshalSSZ(block.Altair, ssz); err != nil {
 			return nil, fmt.Errorf("failed to decode altair signed beacon block: %v", err)
 		}
 	case spec.DataVersionBellatrix:
 		block.Bellatrix = &bellatrix.SignedBeaconBlock{}
-		if err := block.Bellatrix.UnmarshalSSZ(ssz); err != nil {
+		if err := dynSsz.UnmarshalSSZ(block.Bellatrix, ssz); err != nil {
 			return nil, fmt.Errorf("failed to decode bellatrix signed beacon block: %v", err)
 		}
 	case spec.DataVersionCapella:
 		block.Capella = &capella.SignedBeaconBlock{}
-		if err := block.Capella.UnmarshalSSZ(ssz); err != nil {
+		if err := dynSsz.UnmarshalSSZ(block.Capella, ssz); err != nil {
 			return nil, fmt.Errorf("failed to decode capella signed beacon block: %v", err)
 		}
 	case spec.DataVersionDeneb:
 		block.Deneb = &deneb.SignedBeaconBlock{}
-		if err := block.Deneb.UnmarshalSSZ(ssz); err != nil {
+		if err := dynSsz.UnmarshalSSZ(block.Deneb, ssz); err != nil {
 			return nil, fmt.Errorf("failed to decode deneb signed beacon block: %v", err)
 		}
 	default:
diff --git a/rpc/beaconapi.go b/rpc/beaconapi.go
index 214ffc26..9f6cf6e2 100644
--- a/rpc/beaconapi.go
+++ b/rpc/beaconapi.go
@@ -149,6 +149,7 @@ func (bc *BeaconClient) Initialize() error {
 		http.WithTimeout(10 * time.Minute),
 		// TODO (when upstream PR is merged)
 		//http.WithConnectionCheck(false),
+		http.WithCustomSpecSupport(true),
 	}
 
 	// set log level
@@ -179,6 +180,24 @@ func (bc *BeaconClient) Initialize() error {
 	return nil
 }
 
+func (bc *BeaconClient) GetSpecs() (map[string]any, error) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	provider, isProvider := bc.clientSvc.(eth2client.SpecProvider)
+	if !isProvider {
+		return nil, fmt.Errorf("get spec not supported")
+	}
+	result, err := provider.Spec(ctx, &api.SpecOpts{
+		Common: api.CommonOpts{
+			Timeout: 0,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	return result.Data, nil
+}
+
 func (bc *BeaconClient) GetGenesis() (*v1.Genesis, error) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()