diff --git a/go/metrics.pb.go b/go/metrics.pb.go
index 9805432..2f4930d 100644
--- a/go/metrics.pb.go
+++ b/go/metrics.pb.go
@@ -1,11 +1,14 @@
 // Code generated by protoc-gen-go. DO NOT EDIT.
 // source: metrics.proto
 
-package io_prometheus_client // import "github.com/prometheus/client_model/go"
+package io_prometheus_client
 
-import proto "github.com/golang/protobuf/proto"
-import fmt "fmt"
-import math "math"
+import (
+	fmt "fmt"
+	proto "github.com/golang/protobuf/proto"
+	timestamp "github.com/golang/protobuf/ptypes/timestamp"
+	math "math"
+)
 
 // Reference imports to suppress errors if they are not otherwise used.
 var _ = proto.Marshal
@@ -16,7 +19,7 @@ var _ = math.Inf
 // is compatible with the proto package it is being compiled against.
 // A compilation error at this line likely means your copy of the
 // proto package needs to be updated.
-const _ = proto.ProtoPackageIsVersion2 // please upgrade the proto package
+const _ = proto.ProtoPackageIsVersion3 // please upgrade the proto package
 
 type MetricType int32
 
@@ -35,6 +38,7 @@ var MetricType_name = map[int32]string{
 	3: "UNTYPED",
 	4: "HISTOGRAM",
 }
+
 var MetricType_value = map[string]int32{
 	"COUNTER":   0,
 	"GAUGE":     1,
@@ -48,9 +52,11 @@ func (x MetricType) Enum() *MetricType {
 	*p = x
 	return p
 }
+
 func (x MetricType) String() string {
 	return proto.EnumName(MetricType_name, int32(x))
 }
+
 func (x *MetricType) UnmarshalJSON(data []byte) error {
 	value, err := proto.UnmarshalJSONEnum(MetricType_value, data, "MetricType")
 	if err != nil {
@@ -59,8 +65,9 @@ func (x *MetricType) UnmarshalJSON(data []byte) error {
 	*x = MetricType(value)
 	return nil
 }
+
 func (MetricType) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{0}
+	return fileDescriptor_6039342a2ba47b72, []int{0}
 }
 
 type LabelPair struct {
@@ -75,16 +82,17 @@ func (m *LabelPair) Reset()         { *m = LabelPair{} }
 func (m *LabelPair) String() string { return proto.CompactTextString(m) }
 func (*LabelPair) ProtoMessage()    {}
 func (*LabelPair) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{0}
+	return fileDescriptor_6039342a2ba47b72, []int{0}
 }
+
 func (m *LabelPair) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_LabelPair.Unmarshal(m, b)
 }
 func (m *LabelPair) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_LabelPair.Marshal(b, m, deterministic)
 }
-func (dst *LabelPair) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_LabelPair.Merge(dst, src)
+func (m *LabelPair) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_LabelPair.Merge(m, src)
 }
 func (m *LabelPair) XXX_Size() int {
 	return xxx_messageInfo_LabelPair.Size(m)
@@ -120,16 +128,17 @@ func (m *Gauge) Reset()         { *m = Gauge{} }
 func (m *Gauge) String() string { return proto.CompactTextString(m) }
 func (*Gauge) ProtoMessage()    {}
 func (*Gauge) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{1}
+	return fileDescriptor_6039342a2ba47b72, []int{1}
 }
+
 func (m *Gauge) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Gauge.Unmarshal(m, b)
 }
 func (m *Gauge) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Gauge.Marshal(b, m, deterministic)
 }
-func (dst *Gauge) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Gauge.Merge(dst, src)
+func (m *Gauge) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Gauge.Merge(m, src)
 }
 func (m *Gauge) XXX_Size() int {
 	return xxx_messageInfo_Gauge.Size(m)
@@ -148,26 +157,28 @@ func (m *Gauge) GetValue() float64 {
 }
 
 type Counter struct {
-	Value                *float64 `protobuf:"fixed64,1,opt,name=value" json:"value,omitempty"`
-	XXX_NoUnkeyedLiteral struct{} `json:"-"`
-	XXX_unrecognized     []byte   `json:"-"`
-	XXX_sizecache        int32    `json:"-"`
+	Value                *float64  `protobuf:"fixed64,1,opt,name=value" json:"value,omitempty"`
+	Exemplar             *Exemplar `protobuf:"bytes,2,opt,name=exemplar" json:"exemplar,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}  `json:"-"`
+	XXX_unrecognized     []byte    `json:"-"`
+	XXX_sizecache        int32     `json:"-"`
 }
 
 func (m *Counter) Reset()         { *m = Counter{} }
 func (m *Counter) String() string { return proto.CompactTextString(m) }
 func (*Counter) ProtoMessage()    {}
 func (*Counter) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{2}
+	return fileDescriptor_6039342a2ba47b72, []int{2}
 }
+
 func (m *Counter) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Counter.Unmarshal(m, b)
 }
 func (m *Counter) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Counter.Marshal(b, m, deterministic)
 }
-func (dst *Counter) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Counter.Merge(dst, src)
+func (m *Counter) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Counter.Merge(m, src)
 }
 func (m *Counter) XXX_Size() int {
 	return xxx_messageInfo_Counter.Size(m)
@@ -185,6 +196,13 @@ func (m *Counter) GetValue() float64 {
 	return 0
 }
 
+func (m *Counter) GetExemplar() *Exemplar {
+	if m != nil {
+		return m.Exemplar
+	}
+	return nil
+}
+
 type Quantile struct {
 	Quantile             *float64 `protobuf:"fixed64,1,opt,name=quantile" json:"quantile,omitempty"`
 	Value                *float64 `protobuf:"fixed64,2,opt,name=value" json:"value,omitempty"`
@@ -197,16 +215,17 @@ func (m *Quantile) Reset()         { *m = Quantile{} }
 func (m *Quantile) String() string { return proto.CompactTextString(m) }
 func (*Quantile) ProtoMessage()    {}
 func (*Quantile) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{3}
+	return fileDescriptor_6039342a2ba47b72, []int{3}
 }
+
 func (m *Quantile) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Quantile.Unmarshal(m, b)
 }
 func (m *Quantile) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Quantile.Marshal(b, m, deterministic)
 }
-func (dst *Quantile) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Quantile.Merge(dst, src)
+func (m *Quantile) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Quantile.Merge(m, src)
 }
 func (m *Quantile) XXX_Size() int {
 	return xxx_messageInfo_Quantile.Size(m)
@@ -244,16 +263,17 @@ func (m *Summary) Reset()         { *m = Summary{} }
 func (m *Summary) String() string { return proto.CompactTextString(m) }
 func (*Summary) ProtoMessage()    {}
 func (*Summary) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{4}
+	return fileDescriptor_6039342a2ba47b72, []int{4}
 }
+
 func (m *Summary) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Summary.Unmarshal(m, b)
 }
 func (m *Summary) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Summary.Marshal(b, m, deterministic)
 }
-func (dst *Summary) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Summary.Merge(dst, src)
+func (m *Summary) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Summary.Merge(m, src)
 }
 func (m *Summary) XXX_Size() int {
 	return xxx_messageInfo_Summary.Size(m)
@@ -296,16 +316,17 @@ func (m *Untyped) Reset()         { *m = Untyped{} }
 func (m *Untyped) String() string { return proto.CompactTextString(m) }
 func (*Untyped) ProtoMessage()    {}
 func (*Untyped) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{5}
+	return fileDescriptor_6039342a2ba47b72, []int{5}
 }
+
 func (m *Untyped) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Untyped.Unmarshal(m, b)
 }
 func (m *Untyped) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Untyped.Marshal(b, m, deterministic)
 }
-func (dst *Untyped) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Untyped.Merge(dst, src)
+func (m *Untyped) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Untyped.Merge(m, src)
 }
 func (m *Untyped) XXX_Size() int {
 	return xxx_messageInfo_Untyped.Size(m)
@@ -336,16 +357,17 @@ func (m *Histogram) Reset()         { *m = Histogram{} }
 func (m *Histogram) String() string { return proto.CompactTextString(m) }
 func (*Histogram) ProtoMessage()    {}
 func (*Histogram) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{6}
+	return fileDescriptor_6039342a2ba47b72, []int{6}
 }
+
 func (m *Histogram) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Histogram.Unmarshal(m, b)
 }
 func (m *Histogram) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Histogram.Marshal(b, m, deterministic)
 }
-func (dst *Histogram) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Histogram.Merge(dst, src)
+func (m *Histogram) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Histogram.Merge(m, src)
 }
 func (m *Histogram) XXX_Size() int {
 	return xxx_messageInfo_Histogram.Size(m)
@@ -378,27 +400,29 @@ func (m *Histogram) GetBucket() []*Bucket {
 }
 
 type Bucket struct {
-	CumulativeCount      *uint64  `protobuf:"varint,1,opt,name=cumulative_count,json=cumulativeCount" json:"cumulative_count,omitempty"`
-	UpperBound           *float64 `protobuf:"fixed64,2,opt,name=upper_bound,json=upperBound" json:"upper_bound,omitempty"`
-	XXX_NoUnkeyedLiteral struct{} `json:"-"`
-	XXX_unrecognized     []byte   `json:"-"`
-	XXX_sizecache        int32    `json:"-"`
+	CumulativeCount      *uint64   `protobuf:"varint,1,opt,name=cumulative_count,json=cumulativeCount" json:"cumulative_count,omitempty"`
+	UpperBound           *float64  `protobuf:"fixed64,2,opt,name=upper_bound,json=upperBound" json:"upper_bound,omitempty"`
+	Exemplar             *Exemplar `protobuf:"bytes,3,opt,name=exemplar" json:"exemplar,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}  `json:"-"`
+	XXX_unrecognized     []byte    `json:"-"`
+	XXX_sizecache        int32     `json:"-"`
 }
 
 func (m *Bucket) Reset()         { *m = Bucket{} }
 func (m *Bucket) String() string { return proto.CompactTextString(m) }
 func (*Bucket) ProtoMessage()    {}
 func (*Bucket) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{7}
+	return fileDescriptor_6039342a2ba47b72, []int{7}
 }
+
 func (m *Bucket) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Bucket.Unmarshal(m, b)
 }
 func (m *Bucket) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Bucket.Marshal(b, m, deterministic)
 }
-func (dst *Bucket) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Bucket.Merge(dst, src)
+func (m *Bucket) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Bucket.Merge(m, src)
 }
 func (m *Bucket) XXX_Size() int {
 	return xxx_messageInfo_Bucket.Size(m)
@@ -423,6 +447,68 @@ func (m *Bucket) GetUpperBound() float64 {
 	return 0
 }
 
+func (m *Bucket) GetExemplar() *Exemplar {
+	if m != nil {
+		return m.Exemplar
+	}
+	return nil
+}
+
+type Exemplar struct {
+	Label                []*LabelPair         `protobuf:"bytes,1,rep,name=label" json:"label,omitempty"`
+	Value                *float64             `protobuf:"fixed64,2,opt,name=value" json:"value,omitempty"`
+	Timestamp            *timestamp.Timestamp `protobuf:"bytes,3,opt,name=timestamp" json:"timestamp,omitempty"`
+	XXX_NoUnkeyedLiteral struct{}             `json:"-"`
+	XXX_unrecognized     []byte               `json:"-"`
+	XXX_sizecache        int32                `json:"-"`
+}
+
+func (m *Exemplar) Reset()         { *m = Exemplar{} }
+func (m *Exemplar) String() string { return proto.CompactTextString(m) }
+func (*Exemplar) ProtoMessage()    {}
+func (*Exemplar) Descriptor() ([]byte, []int) {
+	return fileDescriptor_6039342a2ba47b72, []int{8}
+}
+
+func (m *Exemplar) XXX_Unmarshal(b []byte) error {
+	return xxx_messageInfo_Exemplar.Unmarshal(m, b)
+}
+func (m *Exemplar) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
+	return xxx_messageInfo_Exemplar.Marshal(b, m, deterministic)
+}
+func (m *Exemplar) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Exemplar.Merge(m, src)
+}
+func (m *Exemplar) XXX_Size() int {
+	return xxx_messageInfo_Exemplar.Size(m)
+}
+func (m *Exemplar) XXX_DiscardUnknown() {
+	xxx_messageInfo_Exemplar.DiscardUnknown(m)
+}
+
+var xxx_messageInfo_Exemplar proto.InternalMessageInfo
+
+func (m *Exemplar) GetLabel() []*LabelPair {
+	if m != nil {
+		return m.Label
+	}
+	return nil
+}
+
+func (m *Exemplar) GetValue() float64 {
+	if m != nil && m.Value != nil {
+		return *m.Value
+	}
+	return 0
+}
+
+func (m *Exemplar) GetTimestamp() *timestamp.Timestamp {
+	if m != nil {
+		return m.Timestamp
+	}
+	return nil
+}
+
 type Metric struct {
 	Label                []*LabelPair `protobuf:"bytes,1,rep,name=label" json:"label,omitempty"`
 	Gauge                *Gauge       `protobuf:"bytes,2,opt,name=gauge" json:"gauge,omitempty"`
@@ -440,16 +526,17 @@ func (m *Metric) Reset()         { *m = Metric{} }
 func (m *Metric) String() string { return proto.CompactTextString(m) }
 func (*Metric) ProtoMessage()    {}
 func (*Metric) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{8}
+	return fileDescriptor_6039342a2ba47b72, []int{9}
 }
+
 func (m *Metric) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Metric.Unmarshal(m, b)
 }
 func (m *Metric) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_Metric.Marshal(b, m, deterministic)
 }
-func (dst *Metric) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_Metric.Merge(dst, src)
+func (m *Metric) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_Metric.Merge(m, src)
 }
 func (m *Metric) XXX_Size() int {
 	return xxx_messageInfo_Metric.Size(m)
@@ -523,16 +610,17 @@ func (m *MetricFamily) Reset()         { *m = MetricFamily{} }
 func (m *MetricFamily) String() string { return proto.CompactTextString(m) }
 func (*MetricFamily) ProtoMessage()    {}
 func (*MetricFamily) Descriptor() ([]byte, []int) {
-	return fileDescriptor_metrics_c97c9a2b9560cb8f, []int{9}
+	return fileDescriptor_6039342a2ba47b72, []int{10}
 }
+
 func (m *MetricFamily) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_MetricFamily.Unmarshal(m, b)
 }
 func (m *MetricFamily) XXX_Marshal(b []byte, deterministic bool) ([]byte, error) {
 	return xxx_messageInfo_MetricFamily.Marshal(b, m, deterministic)
 }
-func (dst *MetricFamily) XXX_Merge(src proto.Message) {
-	xxx_messageInfo_MetricFamily.Merge(dst, src)
+func (m *MetricFamily) XXX_Merge(src proto.Message) {
+	xxx_messageInfo_MetricFamily.Merge(m, src)
 }
 func (m *MetricFamily) XXX_Size() int {
 	return xxx_messageInfo_MetricFamily.Size(m)
@@ -572,6 +660,7 @@ func (m *MetricFamily) GetMetric() []*Metric {
 }
 
 func init() {
+	proto.RegisterEnum("io.prometheus.client.MetricType", MetricType_name, MetricType_value)
 	proto.RegisterType((*LabelPair)(nil), "io.prometheus.client.LabelPair")
 	proto.RegisterType((*Gauge)(nil), "io.prometheus.client.Gauge")
 	proto.RegisterType((*Counter)(nil), "io.prometheus.client.Counter")
@@ -580,50 +669,55 @@ func init() {
 	proto.RegisterType((*Untyped)(nil), "io.prometheus.client.Untyped")
 	proto.RegisterType((*Histogram)(nil), "io.prometheus.client.Histogram")
 	proto.RegisterType((*Bucket)(nil), "io.prometheus.client.Bucket")
+	proto.RegisterType((*Exemplar)(nil), "io.prometheus.client.Exemplar")
 	proto.RegisterType((*Metric)(nil), "io.prometheus.client.Metric")
 	proto.RegisterType((*MetricFamily)(nil), "io.prometheus.client.MetricFamily")
-	proto.RegisterEnum("io.prometheus.client.MetricType", MetricType_name, MetricType_value)
 }
 
-func init() { proto.RegisterFile("metrics.proto", fileDescriptor_metrics_c97c9a2b9560cb8f) }
-
-var fileDescriptor_metrics_c97c9a2b9560cb8f = []byte{
-	// 591 bytes of a gzipped FileDescriptorProto
-	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x54, 0x4f, 0x4f, 0xdb, 0x4e,
-	0x14, 0xfc, 0x99, 0xd8, 0x09, 0x7e, 0x86, 0x5f, 0xad, 0x15, 0x07, 0xab, 0x2d, 0x25, 0xcd, 0x89,
-	0xf6, 0x10, 0x54, 0x04, 0xaa, 0x44, 0xdb, 0x03, 0x50, 0x1a, 0x2a, 0xd5, 0x40, 0x37, 0xc9, 0x81,
-	0x5e, 0xac, 0x8d, 0x59, 0x25, 0x56, 0xbd, 0xb6, 0x6b, 0xef, 0x22, 0xe5, 0xdc, 0x43, 0xbf, 0x47,
-	0xbf, 0x68, 0xab, 0xfd, 0xe3, 0x18, 0x24, 0xc3, 0xa9, 0xb7, 0xb7, 0xf3, 0x66, 0xde, 0x8e, 0x77,
-	0xc7, 0x0b, 0x9b, 0x8c, 0xf2, 0x32, 0x89, 0xab, 0x61, 0x51, 0xe6, 0x3c, 0x47, 0x5b, 0x49, 0x2e,
-	0x2b, 0x46, 0xf9, 0x82, 0x8a, 0x6a, 0x18, 0xa7, 0x09, 0xcd, 0xf8, 0xe0, 0x10, 0xdc, 0x2f, 0x64,
-	0x46, 0xd3, 0x2b, 0x92, 0x94, 0x08, 0x81, 0x9d, 0x11, 0x46, 0x03, 0xab, 0x6f, 0xed, 0xba, 0x58,
-	0xd5, 0x68, 0x0b, 0x9c, 0x5b, 0x92, 0x0a, 0x1a, 0xac, 0x29, 0x50, 0x2f, 0x06, 0xdb, 0xe0, 0x8c,
-	0x88, 0x98, 0xdf, 0x69, 0x4b, 0x8d, 0x55, 0xb7, 0x77, 0xa0, 0x77, 0x9a, 0x8b, 0x8c, 0xd3, 0xf2,
-	0x01, 0xc2, 0x7b, 0x58, 0xff, 0x2a, 0x48, 0xc6, 0x93, 0x94, 0xa2, 0xa7, 0xb0, 0xfe, 0xc3, 0xd4,
-	0x86, 0xb4, 0x5a, 0xdf, 0xdf, 0x7d, 0xa5, 0xfe, 0x65, 0x41, 0x6f, 0x2c, 0x18, 0x23, 0xe5, 0x12,
-	0xbd, 0x84, 0x8d, 0x8a, 0xb0, 0x22, 0xa5, 0x51, 0x2c, 0x77, 0x54, 0x13, 0x6c, 0xec, 0x69, 0x4c,
-	0x99, 0x40, 0xdb, 0x00, 0x86, 0x52, 0x09, 0x66, 0x26, 0xb9, 0x1a, 0x19, 0x0b, 0x86, 0x8e, 0xee,
-	0xec, 0xdf, 0xe9, 0x77, 0x76, 0xbd, 0xfd, 0x17, 0xc3, 0xb6, 0xb3, 0x1a, 0xd6, 0x8e, 0x1b, 0x7f,
-	0xf2, 0x43, 0xa7, 0x19, 0x5f, 0x16, 0xf4, 0xe6, 0x81, 0x0f, 0xfd, 0x69, 0x81, 0x7b, 0x9e, 0x54,
-	0x3c, 0x9f, 0x97, 0x84, 0xfd, 0x03, 0xb3, 0x07, 0xd0, 0x9d, 0x89, 0xf8, 0x3b, 0xe5, 0xc6, 0xea,
-	0xf3, 0x76, 0xab, 0x27, 0x8a, 0x83, 0x0d, 0x77, 0x30, 0x81, 0xae, 0x46, 0xd0, 0x2b, 0xf0, 0x63,
-	0xc1, 0x44, 0x4a, 0x78, 0x72, 0x7b, 0xdf, 0xc5, 0x93, 0x06, 0xd7, 0x4e, 0x76, 0xc0, 0x13, 0x45,
-	0x41, 0xcb, 0x68, 0x96, 0x8b, 0xec, 0xc6, 0x58, 0x01, 0x05, 0x9d, 0x48, 0x64, 0xf0, 0x67, 0x0d,
-	0xba, 0xa1, 0xca, 0x18, 0x3a, 0x04, 0x27, 0x95, 0x31, 0x0a, 0x2c, 0xe5, 0x6a, 0xa7, 0xdd, 0xd5,
-	0x2a, 0x69, 0x58, 0xb3, 0xd1, 0x1b, 0x70, 0xe6, 0x32, 0x46, 0x6a, 0xb8, 0xb7, 0xff, 0xac, 0x5d,
-	0xa6, 0x92, 0x86, 0x35, 0x13, 0xbd, 0x85, 0x5e, 0xac, 0xa3, 0x15, 0x74, 0x94, 0x68, 0xbb, 0x5d,
-	0x64, 0xf2, 0x87, 0x6b, 0xb6, 0x14, 0x56, 0x3a, 0x33, 0x81, 0xfd, 0x98, 0xd0, 0x04, 0x0b, 0xd7,
-	0x6c, 0x29, 0x14, 0xfa, 0x8e, 0x03, 0xe7, 0x31, 0xa1, 0x09, 0x02, 0xae, 0xd9, 0xe8, 0x03, 0xb8,
-	0x8b, 0xfa, 0xea, 0x83, 0x9e, 0x92, 0x3e, 0x70, 0x30, 0xab, 0x84, 0xe0, 0x46, 0x21, 0xc3, 0xc2,
-	0x13, 0x46, 0x2b, 0x4e, 0x58, 0x11, 0xb1, 0x2a, 0xe8, 0xf6, 0xad, 0xdd, 0x0e, 0xf6, 0x56, 0x58,
-	0x58, 0x0d, 0x7e, 0x5b, 0xb0, 0xa1, 0x6f, 0xe0, 0x13, 0x61, 0x49, 0xba, 0x6c, 0xfd, 0x83, 0x11,
-	0xd8, 0x0b, 0x9a, 0x16, 0xe6, 0x07, 0x56, 0x35, 0x3a, 0x00, 0x5b, 0x7a, 0x54, 0x47, 0xf8, 0xff,
-	0x7e, 0xbf, 0xdd, 0x95, 0x9e, 0x3c, 0x59, 0x16, 0x14, 0x2b, 0xb6, 0x0c, 0x9f, 0x7e, 0x53, 0x02,
-	0xfb, 0xb1, 0xf0, 0x69, 0x1d, 0x36, 0xdc, 0xd7, 0x21, 0x40, 0x33, 0x09, 0x79, 0xd0, 0x3b, 0xbd,
-	0x9c, 0x5e, 0x4c, 0xce, 0xb0, 0xff, 0x1f, 0x72, 0xc1, 0x19, 0x1d, 0x4f, 0x47, 0x67, 0xbe, 0x25,
-	0xf1, 0xf1, 0x34, 0x0c, 0x8f, 0xf1, 0xb5, 0xbf, 0x26, 0x17, 0xd3, 0x8b, 0xc9, 0xf5, 0xd5, 0xd9,
-	0x47, 0xbf, 0x83, 0x36, 0xc1, 0x3d, 0xff, 0x3c, 0x9e, 0x5c, 0x8e, 0xf0, 0x71, 0xe8, 0xdb, 0x27,
-	0x18, 0x5a, 0x5f, 0xb2, 0x6f, 0x47, 0xf3, 0x84, 0x2f, 0xc4, 0x6c, 0x18, 0xe7, 0x6c, 0xaf, 0xe9,
-	0xee, 0xe9, 0x6e, 0xc4, 0xf2, 0x1b, 0x9a, 0xee, 0xcd, 0xf3, 0x77, 0x49, 0x1e, 0x35, 0xdd, 0x48,
-	0x77, 0xff, 0x06, 0x00, 0x00, 0xff, 0xff, 0x45, 0x21, 0x7f, 0x64, 0x2b, 0x05, 0x00, 0x00,
+func init() { proto.RegisterFile("metrics.proto", fileDescriptor_6039342a2ba47b72) }
+
+var fileDescriptor_6039342a2ba47b72 = []byte{
+	// 665 bytes of a gzipped FileDescriptorProto
+	0x1f, 0x8b, 0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0xff, 0xac, 0x54, 0xcd, 0x6e, 0xd3, 0x4c,
+	0x14, 0xfd, 0xdc, 0x38, 0x3f, 0xbe, 0x69, 0x3f, 0xa2, 0x51, 0x17, 0x56, 0xa1, 0x24, 0x78, 0x55,
+	0x58, 0x38, 0xa2, 0x6a, 0x05, 0x2a, 0xb0, 0x68, 0x4b, 0x48, 0x91, 0x48, 0x5b, 0x26, 0xc9, 0xa2,
+	0xb0, 0x88, 0x1c, 0x77, 0x70, 0x2c, 0x3c, 0xb1, 0xb1, 0x67, 0x2a, 0xb2, 0x66, 0xc1, 0x16, 0x5e,
+	0x81, 0x17, 0x05, 0xcd, 0x8f, 0x6d, 0x2a, 0xb9, 0x95, 0x40, 0xec, 0x66, 0xee, 0x3d, 0xe7, 0xfa,
+	0xcc, 0xf8, 0x9c, 0x81, 0x0d, 0x4a, 0x58, 0x1a, 0xfa, 0x99, 0x9b, 0xa4, 0x31, 0x8b, 0xd1, 0x66,
+	0x18, 0x8b, 0x15, 0x25, 0x6c, 0x41, 0x78, 0xe6, 0xfa, 0x51, 0x48, 0x96, 0x6c, 0xab, 0x1b, 0xc4,
+	0x71, 0x10, 0x91, 0xbe, 0xc4, 0xcc, 0xf9, 0x87, 0x3e, 0x0b, 0x29, 0xc9, 0x98, 0x47, 0x13, 0x45,
+	0x73, 0xf6, 0xc1, 0x7a, 0xe3, 0xcd, 0x49, 0x74, 0xee, 0x85, 0x29, 0x42, 0x60, 0x2e, 0x3d, 0x4a,
+	0x6c, 0xa3, 0x67, 0xec, 0x58, 0x58, 0xae, 0xd1, 0x26, 0xd4, 0xaf, 0xbc, 0x88, 0x13, 0x7b, 0x4d,
+	0x16, 0xd5, 0xc6, 0xd9, 0x86, 0xfa, 0xd0, 0xe3, 0xc1, 0x6f, 0x6d, 0xc1, 0x31, 0xf2, 0xf6, 0x7b,
+	0x68, 0x1e, 0xc7, 0x7c, 0xc9, 0x48, 0x5a, 0x0d, 0x40, 0x07, 0xd0, 0x22, 0x9f, 0x09, 0x4d, 0x22,
+	0x2f, 0x95, 0x83, 0xdb, 0xbb, 0xf7, 0xdd, 0xaa, 0x03, 0xb8, 0x03, 0x8d, 0xc2, 0x05, 0xde, 0x79,
+	0x0e, 0xad, 0xb7, 0xdc, 0x5b, 0xb2, 0x30, 0x22, 0x68, 0x0b, 0x5a, 0x9f, 0xf4, 0x5a, 0x7f, 0xa0,
+	0xd8, 0x5f, 0x57, 0x5e, 0x48, 0xfb, 0x6a, 0x40, 0x73, 0xcc, 0x29, 0xf5, 0xd2, 0x15, 0x7a, 0x00,
+	0xeb, 0x99, 0x47, 0x93, 0x88, 0xcc, 0x7c, 0xa1, 0x56, 0x4e, 0x30, 0x71, 0x5b, 0xd5, 0xe4, 0x01,
+	0xd0, 0x36, 0x80, 0x86, 0x64, 0x9c, 0xea, 0x49, 0x96, 0xaa, 0x8c, 0x39, 0x15, 0xe7, 0x28, 0xbe,
+	0x5f, 0xeb, 0xd5, 0x6e, 0x3e, 0x47, 0xae, 0xb8, 0xd4, 0xe7, 0x74, 0xa1, 0x39, 0x5d, 0xb2, 0x55,
+	0x42, 0x2e, 0x6f, 0xb8, 0xc5, 0x2f, 0x06, 0x58, 0x27, 0x61, 0xc6, 0xe2, 0x20, 0xf5, 0xe8, 0x3f,
+	0x10, 0xbb, 0x07, 0x8d, 0x39, 0xf7, 0x3f, 0x12, 0xa6, 0xa5, 0xde, 0xab, 0x96, 0x7a, 0x24, 0x31,
+	0x58, 0x63, 0x9d, 0x6f, 0x06, 0x34, 0x54, 0x09, 0x3d, 0x84, 0x8e, 0xcf, 0x29, 0x8f, 0x3c, 0x16,
+	0x5e, 0x5d, 0x97, 0x71, 0xa7, 0xac, 0x2b, 0x29, 0x5d, 0x68, 0xf3, 0x24, 0x21, 0xe9, 0x6c, 0x1e,
+	0xf3, 0xe5, 0xa5, 0xd6, 0x02, 0xb2, 0x74, 0x24, 0x2a, 0xd7, 0x1c, 0x50, 0xfb, 0x43, 0x07, 0x7c,
+	0x37, 0xa0, 0x95, 0x97, 0xd1, 0x3e, 0xd4, 0x23, 0xe1, 0x60, 0xdb, 0x90, 0x87, 0xea, 0x56, 0x4f,
+	0x29, 0x4c, 0x8e, 0x15, 0xba, 0xda, 0x1d, 0xe8, 0x29, 0x58, 0x45, 0x42, 0xb4, 0xac, 0x2d, 0x57,
+	0x65, 0xc8, 0xcd, 0x33, 0xe4, 0x4e, 0x72, 0x04, 0x2e, 0xc1, 0xce, 0xcf, 0x35, 0x68, 0x8c, 0x64,
+	0x22, 0xff, 0x56, 0xd1, 0x63, 0xa8, 0x07, 0x22, 0x53, 0x3a, 0x10, 0x77, 0xab, 0x69, 0x32, 0x76,
+	0x58, 0x21, 0xd1, 0x13, 0x68, 0xfa, 0x2a, 0x67, 0x5a, 0xec, 0x76, 0x35, 0x49, 0x87, 0x11, 0xe7,
+	0x68, 0x41, 0xcc, 0x54, 0x08, 0x6c, 0xf3, 0x36, 0xa2, 0x4e, 0x0a, 0xce, 0xd1, 0x82, 0xc8, 0x95,
+	0x69, 0xed, 0xfa, 0x6d, 0x44, 0xed, 0x6c, 0x9c, 0xa3, 0xd1, 0x0b, 0xb0, 0x16, 0xb9, 0x97, 0xed,
+	0xa6, 0xa4, 0xde, 0x70, 0x31, 0x85, 0xe5, 0x71, 0xc9, 0x10, 0xee, 0x2f, 0xee, 0x7a, 0x46, 0x33,
+	0xbb, 0xd1, 0x33, 0x76, 0x6a, 0xb8, 0x5d, 0xd4, 0x46, 0x99, 0xf3, 0xc3, 0x80, 0x75, 0xf5, 0x07,
+	0x5e, 0x79, 0x34, 0x8c, 0x56, 0x95, 0xcf, 0x19, 0x02, 0x73, 0x41, 0xa2, 0x44, 0xbf, 0x66, 0x72,
+	0x8d, 0xf6, 0xc0, 0x14, 0x1a, 0xe5, 0x15, 0xfe, 0xbf, 0xdb, 0xab, 0x56, 0xa5, 0x26, 0x4f, 0x56,
+	0x09, 0xc1, 0x12, 0x2d, 0xd2, 0xa4, 0x5e, 0x60, 0xdb, 0xbc, 0x2d, 0x4d, 0x8a, 0x87, 0x35, 0xf6,
+	0xd1, 0x08, 0xa0, 0x9c, 0x84, 0xda, 0xd0, 0x3c, 0x3e, 0x9b, 0x9e, 0x4e, 0x06, 0xb8, 0xf3, 0x1f,
+	0xb2, 0xa0, 0x3e, 0x3c, 0x9c, 0x0e, 0x07, 0x1d, 0x43, 0xd4, 0xc7, 0xd3, 0xd1, 0xe8, 0x10, 0x5f,
+	0x74, 0xd6, 0xc4, 0x66, 0x7a, 0x3a, 0xb9, 0x38, 0x1f, 0xbc, 0xec, 0xd4, 0xd0, 0x06, 0x58, 0x27,
+	0xaf, 0xc7, 0x93, 0xb3, 0x21, 0x3e, 0x1c, 0x75, 0xcc, 0x23, 0x0c, 0x95, 0xef, 0xfe, 0xbb, 0x83,
+	0x20, 0x64, 0x0b, 0x3e, 0x77, 0xfd, 0x98, 0xf6, 0xcb, 0x6e, 0x5f, 0x75, 0x67, 0x34, 0xbe, 0x24,
+	0x51, 0x3f, 0x88, 0x9f, 0x85, 0xf1, 0xac, 0xec, 0xce, 0x54, 0xf7, 0x57, 0x00, 0x00, 0x00, 0xff,
+	0xff, 0xd0, 0x84, 0x91, 0x73, 0x59, 0x06, 0x00, 0x00,
 }
diff --git a/metrics.proto b/metrics.proto
index 31633b3..c9546f1 100644
--- a/metrics.proto
+++ b/metrics.proto
@@ -17,6 +17,8 @@ package io.prometheus.client;
 option java_package = "io.prometheus.client";
 option go_package = "github.com/prometheus/client_model/go;io_prometheus_client";
 
+import "google/protobuf/timestamp.proto";
+
 message LabelPair {
   optional string name  = 1;
   optional string value = 2;
@@ -35,7 +37,8 @@ message Gauge {
 }
 
 message Counter {
-  optional double value = 1;
+  optional double   value    = 1;
+  optional Exemplar exemplar = 2;
 }
 
 message Quantile {
@@ -60,8 +63,15 @@ message Histogram {
 }
 
 message Bucket {
-  optional uint64 cumulative_count = 1; // Cumulative in increasing order.
-  optional double upper_bound = 2;      // Inclusive.
+  optional uint64   cumulative_count = 1; // Cumulative in increasing order.
+  optional double   upper_bound      = 2; // Inclusive.
+  optional Exemplar exemplar         = 3;
+}
+
+message Exemplar {
+  repeated LabelPair                 label     = 1;
+  optional double                    value     = 2;
+  optional google.protobuf.Timestamp timestamp = 3; // OpenMetrics-style.
 }
 
 message Metric {