diff --git a/quic/v3/datagram.go b/quic/v3/datagram.go
new file mode 100644
index 00000000..d5c2ac1b
--- /dev/null
+++ b/quic/v3/datagram.go
@@ -0,0 +1,372 @@
+package v3
+
+import (
+	"encoding/binary"
+	"net/netip"
+	"time"
+)
+
+type DatagramType byte
+
+const (
+	// UDP Registration
+	UDPSessionRegistrationType DatagramType = 0x0
+	// UDP Session Payload
+	UDPSessionPayloadType DatagramType = 0x1
+	// DatagramTypeICMP (supporting both ICMPv4 and ICMPv6)
+	ICMPType DatagramType = 0x2
+	// UDP Session Registration Response
+	UDPSessionRegistrationResponseType DatagramType = 0x3
+)
+
+const (
+	// Total number of bytes representing the [DatagramType]
+	datagramTypeLen = 1
+
+	// 1280 is the default datagram packet length used before MTU discovery: https://github.com/quic-go/quic-go/blob/v0.45.0/internal/protocol/params.go#L12
+	maxDatagramLen = 1280
+)
+
+func parseDatagramType(data []byte) (DatagramType, error) {
+	if len(data) < datagramTypeLen {
+		return 0, ErrDatagramHeaderTooSmall
+	}
+	return DatagramType(data[0]), nil
+}
+
+// UDPSessionRegistrationDatagram handles a request to initialize a UDP session on the remote client.
+type UDPSessionRegistrationDatagram struct {
+	RequestID        RequestID
+	Dest             netip.AddrPort
+	Traced           bool
+	IdleDurationHint time.Duration
+	Payload          []byte
+}
+
+const (
+	sessionRegistrationFlagsIPMask      byte = 0b0000_0001
+	sessionRegistrationFlagsTracedMask  byte = 0b0000_0010
+	sessionRegistrationFlagsBundledMask byte = 0b0000_0100
+
+	sessionRegistrationIPv4DatagramHeaderLen = datagramTypeLen +
+		1 + // Flag length
+		2 + // Destination port length
+		2 + // Idle duration seconds length
+		datagramRequestIdLen + // Request ID length
+		4 // IPv4 address length
+
+	// The IPv4 and IPv6 address share space, so adding 12 to the header length gets the space taken by the IPv6 field.
+	sessionRegistrationIPv6DatagramHeaderLen = sessionRegistrationIPv4DatagramHeaderLen + 12
+)
+
+// The datagram structure for UDPSessionRegistrationDatagram is:
+//
+//   0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  0|      Type     |     Flags     |       Destination Port        |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  4|     Idle Duration Seconds     |                               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
+//  8|                                                               |
+//   +                       Session Identifier                      +
+// 12|                           (16 Bytes)                          |
+//   +                                                               +
+// 16|                                                               |
+//   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 20|                               |   Destination IPv4 Address    |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - - - - - - - - -+
+// 24| Destination IPv4 Address cont |                               |
+//   +- - - - - - - - - - - - - - - -                                +
+// 28|                   Destination IPv6 Address                    |
+//   +                  (extension of IPv4 region)                   +
+// 32|                                                               |
+//   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 36|                               |                               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
+//   .                                                               .
+//   .                         Bundle Payload                        .
+//   .                                                               .
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+func (s *UDPSessionRegistrationDatagram) MarshalBinary() (data []byte, err error) {
+	ipv6 := s.Dest.Addr().Is6()
+	var flags byte
+	if s.Traced {
+		flags |= sessionRegistrationFlagsTracedMask
+	}
+	hasPayload := len(s.Payload) > 0
+	if hasPayload {
+		flags |= sessionRegistrationFlagsBundledMask
+	}
+	var maxPayloadLen int
+	if ipv6 {
+		maxPayloadLen = maxDatagramLen - sessionRegistrationIPv6DatagramHeaderLen
+		flags |= sessionRegistrationFlagsIPMask
+	} else {
+		maxPayloadLen = maxDatagramLen - sessionRegistrationIPv4DatagramHeaderLen
+	}
+	// Make sure that the payload being bundled can actually fit in the payload destination
+	if len(s.Payload) > maxPayloadLen {
+		return nil, wrapMarshalErr(ErrDatagramPayloadTooLarge)
+	}
+	// Allocate the buffer with the right size for the destination IP family
+	if ipv6 {
+		data = make([]byte, sessionRegistrationIPv6DatagramHeaderLen+len(s.Payload))
+	} else {
+		data = make([]byte, sessionRegistrationIPv4DatagramHeaderLen+len(s.Payload))
+	}
+	data[0] = byte(UDPSessionRegistrationType)
+	data[1] = byte(flags)
+	binary.BigEndian.PutUint16(data[2:4], s.Dest.Port())
+	binary.BigEndian.PutUint16(data[4:6], uint16(s.IdleDurationHint.Seconds()))
+	err = s.RequestID.MarshalBinaryTo(data[6:22])
+	if err != nil {
+		return nil, wrapMarshalErr(err)
+	}
+	var end int
+	if ipv6 {
+		copy(data[22:38], s.Dest.Addr().AsSlice())
+		end = 38
+	} else {
+		copy(data[22:26], s.Dest.Addr().AsSlice())
+		end = 26
+	}
+
+	if hasPayload {
+		copy(data[end:], s.Payload)
+	}
+
+	return data, nil
+}
+
+func (s *UDPSessionRegistrationDatagram) UnmarshalBinary(data []byte) error {
+	datagramType, err := parseDatagramType(data)
+	if err != nil {
+		return err
+	}
+	if datagramType != UDPSessionRegistrationType {
+		return wrapUnmarshalErr(ErrInvalidDatagramType)
+	}
+
+	requestID, err := RequestIDFromSlice(data[6:22])
+	if err != nil {
+		return wrapUnmarshalErr(err)
+	}
+
+	traced := (data[1] & sessionRegistrationFlagsTracedMask) == sessionRegistrationFlagsTracedMask
+	bundled := (data[1] & sessionRegistrationFlagsBundledMask) == sessionRegistrationFlagsBundledMask
+	ipv6 := (data[1] & sessionRegistrationFlagsIPMask) == sessionRegistrationFlagsIPMask
+
+	port := binary.BigEndian.Uint16(data[2:4])
+	var datagramHeaderSize int
+	var dest netip.AddrPort
+	if ipv6 {
+		datagramHeaderSize = sessionRegistrationIPv6DatagramHeaderLen
+		dest = netip.AddrPortFrom(netip.AddrFrom16([16]byte(data[22:38])), port)
+	} else {
+		datagramHeaderSize = sessionRegistrationIPv4DatagramHeaderLen
+		dest = netip.AddrPortFrom(netip.AddrFrom4([4]byte(data[22:26])), port)
+	}
+
+	idle := time.Duration(binary.BigEndian.Uint16(data[4:6])) * time.Second
+
+	var payload []byte
+	if bundled && len(data) >= datagramHeaderSize && len(data[datagramHeaderSize:]) > 0 {
+		payload = data[datagramHeaderSize:]
+	}
+
+	*s = UDPSessionRegistrationDatagram{
+		RequestID:        requestID,
+		Dest:             dest,
+		Traced:           traced,
+		IdleDurationHint: idle,
+		Payload:          payload,
+	}
+	return nil
+}
+
+// UDPSessionPayloadDatagram provides the payload for a session to be send to either the origin or the client.
+type UDPSessionPayloadDatagram struct {
+	RequestID RequestID
+	Payload   []byte
+}
+
+const (
+	datagramPayloadHeaderLen = datagramTypeLen + datagramRequestIdLen
+
+	// The maximum size that a proxied UDP payload can be in a [UDPSessionPayloadDatagram]
+	maxPayloadPlusHeaderLen = maxDatagramLen - datagramPayloadHeaderLen
+)
+
+// The datagram structure for UDPSessionPayloadDatagram is:
+//
+//   0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  0|      Type     |                                               |
+//   +-+-+-+-+-+-+-+-+                                               +
+//  4|                                                               |
+//   +                                                               +
+//  8|                      Session Identifier                       |
+//   +                           (16 Bytes)                          +
+// 12|                                                               |
+//   +                                               +-+-+-+-+-+-+-+-+
+// 16|                                               |               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               +
+//   .                                                               .
+//   .                             Payload                           .
+//   .                                                               .
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+// MarshalPayloadHeaderTo provides a way to insert the Session Payload header into an already existing byte slice
+// without having to allocate and copy the payload into the destination.
+//
+// This method should be used in-place of MarshalBinary which will allocate in-place the required byte array to return.
+func MarshalPayloadHeaderTo(requestID RequestID, payload []byte) error {
+	if len(payload) < 17 {
+		return wrapMarshalErr(ErrDatagramPayloadHeaderTooSmall)
+	}
+	payload[0] = byte(UDPSessionPayloadType)
+	return requestID.MarshalBinaryTo(payload[1:17])
+}
+
+func (s *UDPSessionPayloadDatagram) UnmarshalBinary(data []byte) error {
+	datagramType, err := parseDatagramType(data)
+	if err != nil {
+		return err
+	}
+	if datagramType != UDPSessionPayloadType {
+		return wrapUnmarshalErr(ErrInvalidDatagramType)
+	}
+
+	// Make sure that the slice provided is the right size to be parsed.
+	if len(data) < 17 || len(data) > maxPayloadPlusHeaderLen {
+		return wrapUnmarshalErr(ErrDatagramPayloadInvalidSize)
+	}
+
+	requestID, err := RequestIDFromSlice(data[1:17])
+	if err != nil {
+		return wrapUnmarshalErr(err)
+	}
+
+	*s = UDPSessionPayloadDatagram{
+		RequestID: requestID,
+		Payload:   data[17:],
+	}
+	return nil
+}
+
+// UDPSessionRegistrationResponseDatagram is used to either return a successful registration or error to the client
+// that requested the registration of a UDP session.
+type UDPSessionRegistrationResponseDatagram struct {
+	RequestID    RequestID
+	ResponseType SessionRegistrationResp
+	ErrorMsg     string
+}
+
+const (
+	datagramRespTypeLen   = 1
+	datagramRespErrMsgLen = 2
+
+	datagramSessionRegistrationResponseLen = datagramTypeLen + datagramRespTypeLen + datagramRequestIdLen + datagramRespErrMsgLen
+
+	// The maximum size that an error message can be in a [UDPSessionRegistrationResponseDatagram].
+	maxResponseErrorMessageLen = maxDatagramLen - datagramSessionRegistrationResponseLen
+)
+
+// SessionRegistrationResp represents all of the responses that a UDP session registration response
+// can return back to the client.
+type SessionRegistrationResp byte
+
+const (
+	// Session was received and is ready to proxy.
+	ResponseOk SessionRegistrationResp = 0x00
+	// Session registration was unable to reach the requested origin destination.
+	ResponseDestinationUnreachable SessionRegistrationResp = 0x01
+	// Session registration was unable to bind to a local UDP socket.
+	ResponseUnableToBindSocket SessionRegistrationResp = 0x02
+	// Session registration failed with an unexpected error but provided a message.
+	ResponseErrorWithMsg SessionRegistrationResp = 0xff
+)
+
+// The datagram structure for UDPSessionRegistrationResponseDatagram is:
+//
+//   0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//  0|      Type     |   Resp Type   |                               |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
+//  4|                                                               |
+//   +                       Session Identifier                      +
+//  8|                           (16 Bytes)                          |
+//   +                                                               +
+// 12|                                                               |
+//   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+// 16|                               |          Error Length         |
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+//   .                                                               .
+//   .                                                               .
+//   .                                                               .
+//   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+func (s *UDPSessionRegistrationResponseDatagram) MarshalBinary() (data []byte, err error) {
+	if len(s.ErrorMsg) > maxResponseErrorMessageLen {
+		return nil, wrapMarshalErr(ErrDatagramResponseMsgInvalidSize)
+	}
+	errMsgLen := uint16(len(s.ErrorMsg))
+
+	data = make([]byte, datagramSessionRegistrationResponseLen+errMsgLen)
+	data[0] = byte(UDPSessionRegistrationResponseType)
+	data[1] = byte(s.ResponseType)
+	err = s.RequestID.MarshalBinaryTo(data[2:18])
+	if err != nil {
+		return nil, wrapMarshalErr(err)
+	}
+
+	if errMsgLen > 0 {
+		binary.BigEndian.PutUint16(data[18:20], errMsgLen)
+		copy(data[20:], []byte(s.ErrorMsg))
+	}
+
+	return data, nil
+}
+
+func (s *UDPSessionRegistrationResponseDatagram) UnmarshalBinary(data []byte) error {
+	datagramType, err := parseDatagramType(data)
+	if err != nil {
+		return wrapUnmarshalErr(err)
+	}
+	if datagramType != UDPSessionRegistrationResponseType {
+		return wrapUnmarshalErr(ErrInvalidDatagramType)
+	}
+
+	if len(data) < datagramSessionRegistrationResponseLen {
+		return wrapUnmarshalErr(ErrDatagramResponseInvalidSize)
+	}
+
+	respType := SessionRegistrationResp(data[1])
+
+	requestID, err := RequestIDFromSlice(data[2:18])
+	if err != nil {
+		return wrapUnmarshalErr(err)
+	}
+
+	errMsgLen := binary.BigEndian.Uint16(data[18:20])
+	if errMsgLen > maxResponseErrorMessageLen {
+		return wrapUnmarshalErr(ErrDatagramResponseMsgTooLargeMaximum)
+	}
+
+	if len(data[20:]) < int(errMsgLen) {
+		return wrapUnmarshalErr(ErrDatagramResponseMsgTooLargeDatagram)
+	}
+
+	var errMsg string
+	if errMsgLen > 0 {
+		errMsg = string(data[20:])
+	}
+
+	*s = UDPSessionRegistrationResponseDatagram{
+		RequestID:    requestID,
+		ResponseType: respType,
+		ErrorMsg:     errMsg,
+	}
+	return nil
+}
diff --git a/quic/v3/datagram_errors.go b/quic/v3/datagram_errors.go
new file mode 100644
index 00000000..244915db
--- /dev/null
+++ b/quic/v3/datagram_errors.go
@@ -0,0 +1,26 @@
+package v3
+
+import (
+	"errors"
+	"fmt"
+)
+
+var (
+	ErrInvalidDatagramType                 error = errors.New("invalid datagram type expected")
+	ErrDatagramHeaderTooSmall              error = fmt.Errorf("datagram should have at least %d bytes", datagramTypeLen)
+	ErrDatagramPayloadTooLarge             error = errors.New("payload length is too large to be bundled in datagram")
+	ErrDatagramPayloadHeaderTooSmall       error = errors.New("payload length is too small to fit the datagram header")
+	ErrDatagramPayloadInvalidSize          error = errors.New("datagram provided is an invalid size")
+	ErrDatagramResponseMsgInvalidSize      error = errors.New("datagram response message is an invalid size")
+	ErrDatagramResponseInvalidSize         error = errors.New("datagram response is an invalid size")
+	ErrDatagramResponseMsgTooLargeMaximum  error = fmt.Errorf("datagram response error message length exceeds the length of the datagram maximum: %d", maxResponseErrorMessageLen)
+	ErrDatagramResponseMsgTooLargeDatagram error = fmt.Errorf("datagram response error message length exceeds the length of the provided datagram")
+)
+
+func wrapMarshalErr(err error) error {
+	return fmt.Errorf("datagram marshal error: %w", err)
+}
+
+func wrapUnmarshalErr(err error) error {
+	return fmt.Errorf("datagram unmarshal error: %w", err)
+}
diff --git a/quic/v3/datagram_test.go b/quic/v3/datagram_test.go
new file mode 100644
index 00000000..b2e77f89
--- /dev/null
+++ b/quic/v3/datagram_test.go
@@ -0,0 +1,352 @@
+package v3_test
+
+import (
+	"encoding/binary"
+	"errors"
+	"net/netip"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	v3 "github.com/cloudflare/cloudflared/quic/v3"
+)
+
+func makePayload(size int) []byte {
+	payload := make([]byte, size)
+	for i := range len(payload) {
+		payload[i] = 0xfc
+	}
+	return payload
+}
+
+func TestSessionRegistration_MarshalUnmarshal(t *testing.T) {
+	payload := makePayload(1254)
+	tests := []*v3.UDPSessionRegistrationDatagram{
+		// Default (IPv4)
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          nil,
+		},
+		// Request ID (max)
+		{
+			RequestID: mustRequestID([16]byte{
+				^uint8(0), ^uint8(0), ^uint8(0), ^uint8(0),
+				^uint8(0), ^uint8(0), ^uint8(0), ^uint8(0),
+				^uint8(0), ^uint8(0), ^uint8(0), ^uint8(0),
+				^uint8(0), ^uint8(0), ^uint8(0), ^uint8(0),
+			}),
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          nil,
+		},
+		// IPv6
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("[fc00::0]:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          nil,
+		},
+		// Traced
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           true,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          nil,
+		},
+		// IdleDurationHint (max)
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 65535 * time.Second,
+			Payload:          nil,
+		},
+		// Payload
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          []byte{0xff, 0xaa, 0xcc, 0x44},
+		},
+		// Payload (max: 1254) for IPv4
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          payload,
+		},
+		// Payload (max: 1242) for IPv4
+		{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 5 * time.Second,
+			Payload:          payload[:1242],
+		},
+	}
+	for _, tt := range tests {
+		marshaled, err := tt.MarshalBinary()
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionRegistrationDatagram{}
+		err = unmarshaled.UnmarshalBinary(marshaled)
+		if err != nil {
+			t.Error(err)
+		}
+		if !compareRegistrationDatagrams(t, tt, &unmarshaled) {
+			t.Errorf("not equal:\n%+v\n%+v", tt, &unmarshaled)
+		}
+	}
+}
+
+func TestSessionRegistration_MarshalBinary(t *testing.T) {
+	t.Run("idle hint too large", func(t *testing.T) {
+		// idle hint duration overflows back to 1
+		datagram := &v3.UDPSessionRegistrationDatagram{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 65537 * time.Second,
+			Payload:          nil,
+		}
+		expected := &v3.UDPSessionRegistrationDatagram{
+			RequestID:        testRequestID,
+			Dest:             netip.MustParseAddrPort("1.1.1.1:8080"),
+			Traced:           false,
+			IdleDurationHint: 1 * time.Second,
+			Payload:          nil,
+		}
+		marshaled, err := datagram.MarshalBinary()
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionRegistrationDatagram{}
+		err = unmarshaled.UnmarshalBinary(marshaled)
+		if err != nil {
+			t.Error(err)
+		}
+		if !compareRegistrationDatagrams(t, expected, &unmarshaled) {
+			t.Errorf("not equal:\n%+v\n%+v", expected, &unmarshaled)
+		}
+	})
+}
+
+func TestTypeUnmarshalErrors(t *testing.T) {
+	t.Run("invalid length", func(t *testing.T) {
+		d1 := v3.UDPSessionRegistrationDatagram{}
+		err := d1.UnmarshalBinary([]byte{})
+		if !errors.Is(err, v3.ErrDatagramHeaderTooSmall) {
+			t.Errorf("expected invalid length to throw error")
+		}
+
+		d2 := v3.UDPSessionPayloadDatagram{}
+		err = d2.UnmarshalBinary([]byte{})
+		if !errors.Is(err, v3.ErrDatagramHeaderTooSmall) {
+			t.Errorf("expected invalid length to throw error")
+		}
+
+		d3 := v3.UDPSessionRegistrationResponseDatagram{}
+		err = d3.UnmarshalBinary([]byte{})
+		if !errors.Is(err, v3.ErrDatagramHeaderTooSmall) {
+			t.Errorf("expected invalid length to throw error")
+		}
+	})
+
+	t.Run("invalid types", func(t *testing.T) {
+		d1 := v3.UDPSessionRegistrationDatagram{}
+		err := d1.UnmarshalBinary([]byte{byte(v3.UDPSessionRegistrationResponseType)})
+		if !errors.Is(err, v3.ErrInvalidDatagramType) {
+			t.Errorf("expected invalid type to throw error")
+		}
+
+		d2 := v3.UDPSessionPayloadDatagram{}
+		err = d2.UnmarshalBinary([]byte{byte(v3.UDPSessionRegistrationType)})
+		if !errors.Is(err, v3.ErrInvalidDatagramType) {
+			t.Errorf("expected invalid type to throw error")
+		}
+
+		d3 := v3.UDPSessionRegistrationResponseDatagram{}
+		err = d3.UnmarshalBinary([]byte{byte(v3.UDPSessionPayloadType)})
+		if !errors.Is(err, v3.ErrInvalidDatagramType) {
+			t.Errorf("expected invalid type to throw error")
+		}
+	})
+}
+
+func TestSessionPayload(t *testing.T) {
+	t.Run("basic", func(t *testing.T) {
+		payload := makePayload(128)
+		err := v3.MarshalPayloadHeaderTo(testRequestID, payload[0:17])
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionPayloadDatagram{}
+		err = unmarshaled.UnmarshalBinary(payload)
+		if err != nil {
+			t.Error(err)
+		}
+		require.Equal(t, testRequestID, unmarshaled.RequestID)
+		require.Equal(t, payload[17:], unmarshaled.Payload)
+	})
+
+	t.Run("empty", func(t *testing.T) {
+		payload := makePayload(17)
+		err := v3.MarshalPayloadHeaderTo(testRequestID, payload)
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionPayloadDatagram{}
+		err = unmarshaled.UnmarshalBinary(payload)
+		if err != nil {
+			t.Error(err)
+		}
+		require.Equal(t, testRequestID, unmarshaled.RequestID)
+		require.Equal(t, payload[17:], unmarshaled.Payload)
+	})
+
+	t.Run("header size too small", func(t *testing.T) {
+		payload := makePayload(16)
+		err := v3.MarshalPayloadHeaderTo(testRequestID, payload)
+		if !errors.Is(err, v3.ErrDatagramPayloadHeaderTooSmall) {
+			t.Errorf("expected an error")
+		}
+	})
+
+	t.Run("payload size too small", func(t *testing.T) {
+		payload := makePayload(17)
+		err := v3.MarshalPayloadHeaderTo(testRequestID, payload)
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionPayloadDatagram{}
+		err = unmarshaled.UnmarshalBinary(payload[:16])
+		if !errors.Is(err, v3.ErrDatagramPayloadInvalidSize) {
+			t.Errorf("expected an error: %s", err)
+		}
+	})
+
+	t.Run("payload size too large", func(t *testing.T) {
+		datagram := makePayload(17 + 1264) // 1263 is the largest payload size allowed
+		err := v3.MarshalPayloadHeaderTo(testRequestID, datagram)
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := v3.UDPSessionPayloadDatagram{}
+		err = unmarshaled.UnmarshalBinary(datagram[:])
+		if !errors.Is(err, v3.ErrDatagramPayloadInvalidSize) {
+			t.Errorf("expected an error: %s", err)
+		}
+	})
+}
+
+func TestSessionRegistrationResponse(t *testing.T) {
+	validRespTypes := []v3.SessionRegistrationResp{
+		v3.ResponseOk,
+		v3.ResponseDestinationUnreachable,
+		v3.ResponseUnableToBindSocket,
+		v3.ResponseErrorWithMsg,
+	}
+	t.Run("basic", func(t *testing.T) {
+		for _, responseType := range validRespTypes {
+			datagram := &v3.UDPSessionRegistrationResponseDatagram{
+				RequestID:    testRequestID,
+				ResponseType: responseType,
+				ErrorMsg:     "test",
+			}
+			marshaled, err := datagram.MarshalBinary()
+			if err != nil {
+				t.Error(err)
+			}
+			unmarshaled := &v3.UDPSessionRegistrationResponseDatagram{}
+			err = unmarshaled.UnmarshalBinary(marshaled)
+			if err != nil {
+				t.Error(err)
+			}
+			require.Equal(t, datagram, unmarshaled)
+		}
+	})
+
+	t.Run("unsupported resp type is valid", func(t *testing.T) {
+		datagram := &v3.UDPSessionRegistrationResponseDatagram{
+			RequestID:    testRequestID,
+			ResponseType: v3.SessionRegistrationResp(0xfc),
+			ErrorMsg:     "",
+		}
+		marshaled, err := datagram.MarshalBinary()
+		if err != nil {
+			t.Error(err)
+		}
+		unmarshaled := &v3.UDPSessionRegistrationResponseDatagram{}
+		err = unmarshaled.UnmarshalBinary(marshaled)
+		if err != nil {
+			t.Error(err)
+		}
+		require.Equal(t, datagram, unmarshaled)
+	})
+
+	t.Run("too small to unmarshal", func(t *testing.T) {
+		payload := makePayload(17)
+		payload[0] = byte(v3.UDPSessionRegistrationResponseType)
+		unmarshaled := &v3.UDPSessionRegistrationResponseDatagram{}
+		err := unmarshaled.UnmarshalBinary(payload)
+		if !errors.Is(err, v3.ErrDatagramResponseInvalidSize) {
+			t.Errorf("expected an error")
+		}
+	})
+
+	t.Run("error message too long", func(t *testing.T) {
+		message := ""
+		for i := 0; i < 1280; i++ {
+			message += "a"
+		}
+		datagram := &v3.UDPSessionRegistrationResponseDatagram{
+			RequestID:    testRequestID,
+			ResponseType: v3.SessionRegistrationResp(0xfc),
+			ErrorMsg:     message,
+		}
+		_, err := datagram.MarshalBinary()
+		if !errors.Is(err, v3.ErrDatagramResponseMsgInvalidSize) {
+			t.Errorf("expected an error")
+		}
+	})
+
+	t.Run("error message too large to unmarshal", func(t *testing.T) {
+		payload := makePayload(1280)
+		payload[0] = byte(v3.UDPSessionRegistrationResponseType)
+		binary.BigEndian.PutUint16(payload[18:20], 1280) // larger than the datagram size could be
+		unmarshaled := &v3.UDPSessionRegistrationResponseDatagram{}
+		err := unmarshaled.UnmarshalBinary(payload)
+		if !errors.Is(err, v3.ErrDatagramResponseMsgTooLargeMaximum) {
+			t.Errorf("expected an error: %v", err)
+		}
+	})
+
+	t.Run("error message larger than provided buffer", func(t *testing.T) {
+		payload := makePayload(1000)
+		payload[0] = byte(v3.UDPSessionRegistrationResponseType)
+		binary.BigEndian.PutUint16(payload[18:20], 1001) // larger than the datagram size provided
+		unmarshaled := &v3.UDPSessionRegistrationResponseDatagram{}
+		err := unmarshaled.UnmarshalBinary(payload)
+		if !errors.Is(err, v3.ErrDatagramResponseMsgTooLargeDatagram) {
+			t.Errorf("expected an error: %v", err)
+		}
+	})
+}
+
+func compareRegistrationDatagrams(t *testing.T, l *v3.UDPSessionRegistrationDatagram, r *v3.UDPSessionRegistrationDatagram) bool {
+	require.Equal(t, l.Payload, r.Payload)
+	return l.RequestID == r.RequestID &&
+		l.Dest == r.Dest &&
+		l.IdleDurationHint == r.IdleDurationHint &&
+		l.Traced == r.Traced
+}
diff --git a/quic/v3/request.go b/quic/v3/request.go
new file mode 100644
index 00000000..29509e83
--- /dev/null
+++ b/quic/v3/request.go
@@ -0,0 +1,72 @@
+package v3
+
+import (
+	"encoding/binary"
+	"errors"
+)
+
+const (
+	datagramRequestIdLen = 16
+)
+
+var (
+	// ErrInvalidRequestIDLen is returned when the provided request id can not be parsed from the provided byte slice.
+	ErrInvalidRequestIDLen error = errors.New("invalid request id length provided")
+	// ErrInvalidPayloadDestLen is returned when the provided destination byte slice cannot fit the whole request id.
+	ErrInvalidPayloadDestLen error = errors.New("invalid payload size provided")
+)
+
+// RequestID is the request-id-v2 identifier, it is used to distinguish between specific flows or sessions proxied
+// from the edge to cloudflared.
+type RequestID uint128
+
+type uint128 struct {
+	hi uint64
+	lo uint64
+}
+
+// RequestIDFromSlice reads a request ID from a byte slice.
+func RequestIDFromSlice(data []byte) (RequestID, error) {
+	if len(data) != datagramRequestIdLen {
+		return RequestID{}, ErrInvalidRequestIDLen
+	}
+
+	return RequestID{
+		hi: binary.BigEndian.Uint64(data[:8]),
+		lo: binary.BigEndian.Uint64(data[8:]),
+	}, nil
+}
+
+// Compare returns an integer comparing two IPs.
+// The result will be 0 if id == id2, -1 if id < id2, and +1 if id > id2.
+// The definition of "less than" is the same as the [RequestID.Less] method.
+func (id RequestID) Compare(id2 RequestID) int {
+	hi1, hi2 := id.hi, id2.hi
+	if hi1 < hi2 {
+		return -1
+	}
+	if hi1 > hi2 {
+		return 1
+	}
+	lo1, lo2 := id.lo, id2.lo
+	if lo1 < lo2 {
+		return -1
+	}
+	if lo1 > lo2 {
+		return 1
+	}
+	return 0
+}
+
+// Less reports whether id sorts before id2.
+func (id RequestID) Less(id2 RequestID) bool { return id.Compare(id2) == -1 }
+
+// MarshalBinaryTo writes the id to the provided destination byte slice; the byte slice must be of at least size 16.
+func (id RequestID) MarshalBinaryTo(data []byte) error {
+	if len(data) < datagramRequestIdLen {
+		return ErrInvalidPayloadDestLen
+	}
+	binary.BigEndian.PutUint64(data[:8], id.hi)
+	binary.BigEndian.PutUint64(data[8:], id.lo)
+	return nil
+}
diff --git a/quic/v3/request_test.go b/quic/v3/request_test.go
new file mode 100644
index 00000000..519c2dd2
--- /dev/null
+++ b/quic/v3/request_test.go
@@ -0,0 +1,50 @@
+package v3_test
+
+import (
+	"crypto/rand"
+	"slices"
+	"testing"
+
+	v3 "github.com/cloudflare/cloudflared/quic/v3"
+)
+
+var (
+	testRequestIDBytes = [16]byte{
+		0x00, 0x11, 0x22, 0x33,
+		0x44, 0x55, 0x66, 0x77,
+		0x88, 0x99, 0xaa, 0xbb,
+		0xcc, 0xdd, 0xee, 0xff,
+	}
+	testRequestID = mustRequestID(testRequestIDBytes)
+)
+
+func mustRequestID(data [16]byte) v3.RequestID {
+	id, err := v3.RequestIDFromSlice(data[:])
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+func TestRequestIDParsing(t *testing.T) {
+	buf1 := make([]byte, 16)
+	n, err := rand.Read(buf1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 16 {
+		t.Fatalf("did not read 16 bytes: %d", n)
+	}
+	id, err := v3.RequestIDFromSlice(buf1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	buf2 := make([]byte, 16)
+	err = id.MarshalBinaryTo(buf2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !slices.Equal(buf1, buf2) {
+		t.Fatalf("buf1 != buf2: %+v %+v", buf1, buf2)
+	}
+}