diff --git a/gen/pb-go/bundle/v1/sigstore_bundle.pb.go b/gen/pb-go/bundle/v1/sigstore_bundle.pb.go
index b3f44d1f..f36cde48 100644
--- a/gen/pb-go/bundle/v1/sigstore_bundle.pb.go
+++ b/gen/pb-go/bundle/v1/sigstore_bundle.pb.go
@@ -24,9 +24,10 @@ import (
 	v1 "github.com/sigstore/protobuf-specs/gen/pb-go/common/v1"
 	dsse "github.com/sigstore/protobuf-specs/gen/pb-go/dsse"
 	v11 "github.com/sigstore/protobuf-specs/gen/pb-go/rekor/v1"
-	_ "google.golang.org/genproto/googleapis/api/annotations"
+	annotations "google.golang.org/genproto/googleapis/api/annotations"
 	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
 	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	descriptorpb "google.golang.org/protobuf/types/descriptorpb"
 	reflect "reflect"
 	sync "sync"
 )
@@ -383,6 +384,23 @@ func (*Bundle_MessageSignature) isBundle_Content() {}
 
 func (*Bundle_DsseEnvelope) isBundle_Content() {}
 
+var file_sigstore_bundle_proto_extTypes = []protoimpl.ExtensionInfo{
+	{
+		ExtendedType:  (*descriptorpb.OneofOptions)(nil),
+		ExtensionType: ([]annotations.FieldBehavior)(nil),
+		Field:         1053,
+		Name:          "dev.sigstore.bundle.v1.oneof_behavior",
+		Tag:           "varint,1053,rep,name=oneof_behavior,enum=google.api.FieldBehavior",
+		Filename:      "sigstore_bundle.proto",
+	},
+}
+
+// Extension fields to descriptorpb.OneofOptions.
+var (
+	// repeated google.api.FieldBehavior oneof_behavior = 1053;
+	E_OneofBehavior = &file_sigstore_bundle_proto_extTypes[0]
+)
+
 var File_sigstore_bundle_proto protoreflect.FileDescriptor
 
 var file_sigstore_bundle_proto_rawDesc = []byte{
@@ -391,78 +409,85 @@ var file_sigstore_bundle_proto_rawDesc = []byte{
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+	0x65, 0x3a, 0x3a, 0x56, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -489,22 +514,26 @@ var file_sigstore_bundle_proto_goTypes = []interface{}{
 	(*v11.TransparencyLogEntry)(nil),  // 7: dev.sigstore.rekor.v1.TransparencyLogEntry
 	(*v1.MessageSignature)(nil),       // 8: dev.sigstore.common.v1.MessageSignature
 	(*dsse.Envelope)(nil),             // 9: io.intoto.Envelope
+	(*descriptorpb.OneofOptions)(nil), // 10: google.protobuf.OneofOptions
+	(annotations.FieldBehavior)(0),    // 11: google.api.FieldBehavior
 }
 var file_sigstore_bundle_proto_depIdxs = []int32{
-	3, // 0: dev.sigstore.bundle.v1.TimestampVerificationData.rfc3161_timestamps:type_name -> dev.sigstore.common.v1.RFC3161SignedTimestamp
-	4, // 1: dev.sigstore.bundle.v1.VerificationMaterial.public_key:type_name -> dev.sigstore.common.v1.PublicKeyIdentifier
-	5, // 2: dev.sigstore.bundle.v1.VerificationMaterial.x509_certificate_chain:type_name -> dev.sigstore.common.v1.X509CertificateChain
-	6, // 3: dev.sigstore.bundle.v1.VerificationMaterial.certificate:type_name -> dev.sigstore.common.v1.X509Certificate
-	7, // 4: dev.sigstore.bundle.v1.VerificationMaterial.tlog_entries:type_name -> dev.sigstore.rekor.v1.TransparencyLogEntry
-	0, // 5: dev.sigstore.bundle.v1.VerificationMaterial.timestamp_verification_data:type_name -> dev.sigstore.bundle.v1.TimestampVerificationData
-	1, // 6: dev.sigstore.bundle.v1.Bundle.verification_material:type_name -> dev.sigstore.bundle.v1.VerificationMaterial
-	8, // 7: dev.sigstore.bundle.v1.Bundle.message_signature:type_name -> dev.sigstore.common.v1.MessageSignature
-	9, // 8: dev.sigstore.bundle.v1.Bundle.dsse_envelope:type_name -> io.intoto.Envelope
-	9, // [9:9] is the sub-list for method output_type
-	9, // [9:9] is the sub-list for method input_type
-	9, // [9:9] is the sub-list for extension type_name
-	9, // [9:9] is the sub-list for extension extendee
-	0, // [0:9] is the sub-list for field type_name
+	3,  // 0: dev.sigstore.bundle.v1.TimestampVerificationData.rfc3161_timestamps:type_name -> dev.sigstore.common.v1.RFC3161SignedTimestamp
+	4,  // 1: dev.sigstore.bundle.v1.VerificationMaterial.public_key:type_name -> dev.sigstore.common.v1.PublicKeyIdentifier
+	5,  // 2: dev.sigstore.bundle.v1.VerificationMaterial.x509_certificate_chain:type_name -> dev.sigstore.common.v1.X509CertificateChain
+	6,  // 3: dev.sigstore.bundle.v1.VerificationMaterial.certificate:type_name -> dev.sigstore.common.v1.X509Certificate
+	7,  // 4: dev.sigstore.bundle.v1.VerificationMaterial.tlog_entries:type_name -> dev.sigstore.rekor.v1.TransparencyLogEntry
+	0,  // 5: dev.sigstore.bundle.v1.VerificationMaterial.timestamp_verification_data:type_name -> dev.sigstore.bundle.v1.TimestampVerificationData
+	1,  // 6: dev.sigstore.bundle.v1.Bundle.verification_material:type_name -> dev.sigstore.bundle.v1.VerificationMaterial
+	8,  // 7: dev.sigstore.bundle.v1.Bundle.message_signature:type_name -> dev.sigstore.common.v1.MessageSignature
+	9,  // 8: dev.sigstore.bundle.v1.Bundle.dsse_envelope:type_name -> io.intoto.Envelope
+	10, // 9: dev.sigstore.bundle.v1.oneof_behavior:extendee -> google.protobuf.OneofOptions
+	11, // 10: dev.sigstore.bundle.v1.oneof_behavior:type_name -> google.api.FieldBehavior
+	11, // [11:11] is the sub-list for method output_type
+	11, // [11:11] is the sub-list for method input_type
+	10, // [10:11] is the sub-list for extension type_name
+	9,  // [9:10] is the sub-list for extension extendee
+	0,  // [0:9] is the sub-list for field type_name
 }
 
 func init() { file_sigstore_bundle_proto_init() }
@@ -566,12 +595,13 @@ func file_sigstore_bundle_proto_init() {
 			RawDescriptor: file_sigstore_bundle_proto_rawDesc,
 			NumEnums:      0,
 			NumMessages:   3,
-			NumExtensions: 0,
+			NumExtensions: 1,
 			NumServices:   0,
 		},
 		GoTypes:           file_sigstore_bundle_proto_goTypes,
 		DependencyIndexes: file_sigstore_bundle_proto_depIdxs,
 		MessageInfos:      file_sigstore_bundle_proto_msgTypes,
+		ExtensionInfos:    file_sigstore_bundle_proto_extTypes,
 	}.Build()
 	File_sigstore_bundle_proto = out.File
 	file_sigstore_bundle_proto_rawDesc = nil
diff --git a/gen/pb-ruby/lib/sigstore_bundle_pb.rb b/gen/pb-ruby/lib/sigstore_bundle_pb.rb
index 08447685..32e44444 100644
--- a/gen/pb-ruby/lib/sigstore_bundle_pb.rb
+++ b/gen/pb-ruby/lib/sigstore_bundle_pb.rb
@@ -4,6 +4,7 @@
 require 'google/protobuf'
 
 require 'google/api/field_behavior_pb'
+require 'google/protobuf/descriptor_pb'
 require 'envelope_pb'
 require 'sigstore_common_pb'
 require 'sigstore_rekor_pb'
diff --git a/gen/pb-rust/sigstore-protobuf-specs/src/generated/file_descriptor_set.bin b/gen/pb-rust/sigstore-protobuf-specs/src/generated/file_descriptor_set.bin
index 71a7c58b..e9ab621c 100644
Binary files a/gen/pb-rust/sigstore-protobuf-specs/src/generated/file_descriptor_set.bin and b/gen/pb-rust/sigstore-protobuf-specs/src/generated/file_descriptor_set.bin differ
diff --git a/protos/sigstore_bundle.proto b/protos/sigstore_bundle.proto
index cd9d6706..4fa465db 100644
--- a/protos/sigstore_bundle.proto
+++ b/protos/sigstore_bundle.proto
@@ -16,6 +16,7 @@ syntax = "proto3";
 package dev.sigstore.bundle.v1;
 
 import "google/api/field_behavior.proto";
+import "google/protobuf/descriptor.proto";
 
 // https://raw.githubusercontent.com/secure-systems-lab/dsse/9c813476bd36de70a5738c72e784f123ecea16af/envelope.proto
 import "envelope.proto";
@@ -28,6 +29,10 @@ option java_multiple_files = true;
 option java_outer_classname = "BundleProto";
 option ruby_package = "Sigstore::Bundle::V1";
 
+extend .google.protobuf.OneofOptions {
+  repeated .google.api.FieldBehavior oneof_behavior = 1053;
+}
+
 // Notes on versioning.
 // The primary message ('Bundle') MUST be versioned, by populating the
 // 'media_type' field. Semver-ish (only major/minor versions) scheme MUST
@@ -91,9 +96,11 @@ message VerificationMaterial {
         // When used in a `0.3` bundle with the PGI and "keyless" signing,
         // form (3) MUST be used.
         oneof content {
-                dev.sigstore.common.v1.PublicKeyIdentifier public_key = 1 [(google.api.field_behavior) = REQUIRED];
-                dev.sigstore.common.v1.X509CertificateChain x509_certificate_chain = 2 [(google.api.field_behavior) = REQUIRED];
-                dev.sigstore.common.v1.X509Certificate certificate = 5 [(google.api.field_behavior) = REQUIRED];
+                option (oneof_behavior) = REQUIRED;
+
+                dev.sigstore.common.v1.PublicKeyIdentifier public_key = 1;
+                dev.sigstore.common.v1.X509CertificateChain x509_certificate_chain = 2;
+                dev.sigstore.common.v1.X509Certificate certificate = 5;
         }
         // An inclusion proof and an optional signed timestamp from the log.
         // Client verification libraries MAY provide an option to support v0.1
@@ -128,7 +135,9 @@ message Bundle {
         // DSSE envelope.
         VerificationMaterial verification_material = 2 [(google.api.field_behavior) = REQUIRED];
         oneof content {
-                dev.sigstore.common.v1.MessageSignature message_signature = 3 [(google.api.field_behavior) = REQUIRED];
+                option (oneof_behavior) = REQUIRED;
+
+                dev.sigstore.common.v1.MessageSignature message_signature = 3;
                 // A DSSE envelope can contain arbitrary payloads.
                 // Verifiers must verify that the payload type is a
                 // supported and expected type. This is part of the DSSE
@@ -142,7 +151,7 @@ message Bundle {
                 //    instance of the required verification materials
                 // During verification a client MUST reject an envelope if
                 // the number of signatures is not equal to one.
-                io.intoto.Envelope dsse_envelope = 4 [(google.api.field_behavior) = REQUIRED];
+                io.intoto.Envelope dsse_envelope = 4;
         }
         // Reserved for future additions of artifact types.
         reserved 5 to 50;