diff --git a/beacon-chain/core/altair/BUILD.bazel b/beacon-chain/core/altair/BUILD.bazel
index 6d0e14bab234..990f9a9fa60c 100644
--- a/beacon-chain/core/altair/BUILD.bazel
+++ b/beacon-chain/core/altair/BUILD.bazel
@@ -16,6 +16,7 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/v3/beacon-chain/core/altair",
     visibility = [
         "//beacon-chain:__subpackages__",
+        "//cmd/prysmctl/testnet:__pkg__",
         "//testing/endtoend/evaluators:__subpackages__",
         "//testing/spectest:__subpackages__",
         "//testing/util:__pkg__",
diff --git a/beacon-chain/core/execution/BUILD.bazel b/beacon-chain/core/execution/BUILD.bazel
index f67f3e1124ca..cf4efff737af 100644
--- a/beacon-chain/core/execution/BUILD.bazel
+++ b/beacon-chain/core/execution/BUILD.bazel
@@ -6,6 +6,7 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/v3/beacon-chain/core/execution",
     visibility = [
         "//beacon-chain:__subpackages__",
+        "//cmd/prysmctl/testnet:__pkg__",
         "//testing/spectest:__subpackages__",
         "//validator/client:__pkg__",
     ],
diff --git a/cmd/flags/BUILD.bazel b/cmd/flags/BUILD.bazel
new file mode 100644
index 000000000000..bbc1a8c67621
--- /dev/null
+++ b/cmd/flags/BUILD.bazel
@@ -0,0 +1,9 @@
+load("@prysm//tools/go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["enum.go"],
+    importpath = "github.com/prysmaticlabs/prysm/v3/cmd/flags",
+    visibility = ["//visibility:public"],
+    deps = ["@com_github_urfave_cli_v2//:go_default_library"],
+)
diff --git a/cmd/flags/enum.go b/cmd/flags/enum.go
new file mode 100644
index 000000000000..7864c63e7e83
--- /dev/null
+++ b/cmd/flags/enum.go
@@ -0,0 +1,47 @@
+package flags
+
+// via https://github.com/urfave/cli/issues/602
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/urfave/cli/v2"
+)
+
+// EnumValue allows the cli to present a fixed set of string values.
+type EnumValue struct {
+	Name        string
+	Usage       string
+	Destination *string
+	Enum        []string
+	Value       string
+}
+
+func (e *EnumValue) Set(value string) error {
+	for _, enum := range e.Enum {
+		if enum == value {
+			*e.Destination = value
+			return nil
+		}
+	}
+
+	return fmt.Errorf("allowed values are %s", strings.Join(e.Enum, ", "))
+}
+
+func (e *EnumValue) String() string {
+	if e.Destination == nil {
+		return e.Value
+	}
+	if *e.Destination == "" {
+		return e.Value
+	}
+	return *e.Destination
+}
+
+// Wraps the EnumValue in a GenericFlag value so that it satisfies the cli.Flag interface.
+func (e EnumValue) GenericFlag() *cli.GenericFlag {
+	*e.Destination = e.Value
+	var i cli.Generic = &e
+	return &cli.GenericFlag{Name: e.Name, Usage: e.Usage, Destination: &i, Value: i}
+}
diff --git a/cmd/prysmctl/testnet/BUILD.bazel b/cmd/prysmctl/testnet/BUILD.bazel
index 81206492c396..7d4c98d87bb5 100644
--- a/cmd/prysmctl/testnet/BUILD.bazel
+++ b/cmd/prysmctl/testnet/BUILD.bazel
@@ -9,13 +9,19 @@ go_library(
     importpath = "github.com/prysmaticlabs/prysm/v3/cmd/prysmctl/testnet",
     visibility = ["//visibility:public"],
     deps = [
+        "//beacon-chain/core/altair:go_default_library",
+        "//beacon-chain/core/capella:go_default_library",
+        "//beacon-chain/core/execution:go_default_library",
+        "//beacon-chain/state:go_default_library",
+        "//beacon-chain/state/state-native:go_default_library",
+        "//cmd/flags:go_default_library",
         "//config/params:go_default_library",
         "//io/file:go_default_library",
         "//proto/prysm/v1alpha1:go_default_library",
         "//runtime/interop:go_default_library",
+        "//runtime/version:go_default_library",
         "@com_github_ghodss_yaml//:go_default_library",
         "@com_github_pkg_errors//:go_default_library",
-        "@com_github_prysmaticlabs_fastssz//:go_default_library",
         "@com_github_sirupsen_logrus//:go_default_library",
         "@com_github_urfave_cli_v2//:go_default_library",
     ],
diff --git a/cmd/prysmctl/testnet/generate_genesis.go b/cmd/prysmctl/testnet/generate_genesis.go
index ade0f7a371cd..e03beb8b516d 100644
--- a/cmd/prysmctl/testnet/generate_genesis.go
+++ b/cmd/prysmctl/testnet/generate_genesis.go
@@ -9,9 +9,16 @@ import (
 	"os"
 	"strings"
 
+	"github.com/prysmaticlabs/prysm/v3/beacon-chain/core/altair"
+	"github.com/prysmaticlabs/prysm/v3/beacon-chain/core/capella"
+	"github.com/prysmaticlabs/prysm/v3/beacon-chain/core/execution"
+	"github.com/prysmaticlabs/prysm/v3/beacon-chain/state"
+	state_native "github.com/prysmaticlabs/prysm/v3/beacon-chain/state/state-native"
+	"github.com/prysmaticlabs/prysm/v3/cmd/flags"
+	"github.com/prysmaticlabs/prysm/v3/runtime/version"
+
 	"github.com/ghodss/yaml"
 	"github.com/pkg/errors"
-	fastssz "github.com/prysmaticlabs/fastssz"
 	"github.com/prysmaticlabs/prysm/v3/config/params"
 	"github.com/prysmaticlabs/prysm/v3/io/file"
 	ethpb "github.com/prysmaticlabs/prysm/v3/proto/prysm/v1alpha1"
@@ -30,6 +37,7 @@ var (
 		OutputSSZ       string
 		OutputJSON      string
 		OutputYaml      string
+		ForkName        string
 	}{}
 	log           = logrus.WithField("prefix", "genesis")
 	outputSSZFlag = &cli.StringFlag{
@@ -82,6 +90,13 @@ var (
 				Destination: &generateGenesisStateFlags.GenesisTime,
 				Usage:       "Unix timestamp seconds used as the genesis time in the genesis state. If unset, defaults to now()",
 			},
+			flags.EnumValue{
+				Name:        "fork",
+				Usage:       fmt.Sprintf("Name of the BeaconState schema to use in output encoding [%s]", strings.Join(versionNames(), ",")),
+				Enum:        versionNames(),
+				Value:       versionNames()[0],
+				Destination: &generateGenesisStateFlags.ForkName,
+			}.GenericFlag(),
 			outputSSZFlag,
 			outputYamlFlag,
 			outputJsonFlag,
@@ -89,6 +104,15 @@ var (
 	}
 )
 
+func versionNames() []string {
+	enum := version.All()
+	names := make([]string, len(enum))
+	for i := range enum {
+		names[i] = version.String(enum[i])
+	}
+	return names
+}
+
 // Represents a json object of hex string and uint64 values for
 // validators on Ethereum. This file can be generated using the official staking-deposit-cli.
 type depositDataJSON struct {
@@ -122,25 +146,33 @@ func cliActionGenerateGenesisState(cliCtx *cli.Context) error {
 	if err != nil {
 		return fmt.Errorf("could not generate genesis state: %v", err)
 	}
+	st, err := upgradeStateToForkName(cliCtx.Context, genesisState, generateGenesisStateFlags.ForkName)
+	if err != nil {
+		return err
+	}
+
 	if outputJson != "" {
-		if err := writeToOutputFile(outputJson, genesisState, json.Marshal); err != nil {
+		if err := writeToOutputFile(outputJson, st, json.Marshal); err != nil {
 			return err
 		}
 	}
 	if outputYaml != "" {
-		if err := writeToOutputFile(outputYaml, genesisState, yaml.Marshal); err != nil {
+		if err := writeToOutputFile(outputYaml, st, yaml.Marshal); err != nil {
 			return err
 		}
 	}
 	if outputSSZ != "" {
+		type MinimumSSZMarshal interface {
+			MarshalSSZ() ([]byte, error)
+		}
 		marshalFn := func(o interface{}) ([]byte, error) {
-			marshaler, ok := o.(fastssz.Marshaler)
+			marshaler, ok := o.(MinimumSSZMarshal)
 			if !ok {
 				return nil, errors.New("not a marshaler")
 			}
 			return marshaler.MarshalSSZ()
 		}
-		if err := writeToOutputFile(outputSSZ, genesisState, marshalFn); err != nil {
+		if err := writeToOutputFile(outputSSZ, st, marshalFn); err != nil {
 			return err
 		}
 	}
@@ -148,6 +180,42 @@ func cliActionGenerateGenesisState(cliCtx *cli.Context) error {
 	return nil
 }
 
+func upgradeStateToForkName(ctx context.Context, pbst *ethpb.BeaconState, name string) (state.BeaconState, error) {
+	st, err := state_native.InitializeFromProtoUnsafePhase0(pbst)
+	if err != nil {
+		return nil, err
+	}
+	if name == "" || name == "phase0" {
+		return st, nil
+	}
+
+	st, err = altair.UpgradeToAltair(ctx, st)
+	if err != nil {
+		return nil, err
+	}
+	if name == "altair" {
+		return st, nil
+	}
+
+	st, err = execution.UpgradeToBellatrix(st)
+	if err != nil {
+		return nil, err
+	}
+	if name == "bellatrix" {
+		return st, nil
+	}
+
+	st, err = capella.UpgradeToCapella(st)
+	if err != nil {
+		return nil, err
+	}
+	if name == "capella" {
+		return st, nil
+	}
+
+	return nil, fmt.Errorf("unrecognized fork name '%s'", name)
+}
+
 func setGlobalParams() error {
 	chainConfigFile := generateGenesisStateFlags.ChainConfigFile
 	if chainConfigFile != "" {
diff --git a/runtime/version/fork.go b/runtime/version/fork.go
index 4a2e4fa922e8..6d4e0d7abd56 100644
--- a/runtime/version/fork.go
+++ b/runtime/version/fork.go
@@ -21,3 +21,8 @@ func String(version int) string {
 		return "unknown version"
 	}
 }
+
+// All returns a list of all known fork versions.
+func All() []int {
+	return []int{Phase0, Altair, Bellatrix, Capella}
+}