[DefaultValue(DefaultBoolean.Default)]
[DXCategory("Behavior")]
public DefaultBoolean AcceptEditorTextAsNewValue { get; set; }

<DXCategory("Behavior")>
<DefaultValue(DefaultBoolean.Default)>
Public Property AcceptEditorTextAsNewValue As DefaultBoolean

using DevExpress.XtraEditors;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Lookup_ComboboxMode {
    public partial class Form1 : Form {
        public Form1() {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e) {
            initLookupEdit();
            initGridLookupEdit();
        }

        void initLookupEdit() {
            lookUpEdit1.EditValueChanged += LookUpEdit1_EditValueChanged; ;
            lookUpEdit1.Properties.NullText = "(select or type value)";

            string[] colors = new string[] {
                "Yellow", "Red", "Green", "Black", "White"
            };

            lookUpEdit1.Properties.DataSource = colors;
            lookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard;
            lookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.Default; //Default is equivalent to True for LookupEdit control
        }

        void initGridLookupEdit() {
            gridLookUpEdit1.EditValueChanged += LookUpEdit1_EditValueChanged;
            gridLookUpEdit1.Properties.NullText = "(select or type value)";

            List<Product> products = new List<Product> {
                new Product(){ ProductName="Chang" },
                new Product(){ ProductName="Ipoh Coffee" },
                new Product(){ ProductName="Ravioli Angelo" },
                new Product(){ ProductName="Filo Mix" },
                new Product(){ ProductName="Tunnbröd" },
                new Product(){ ProductName="Konbu" },
                new Product(){ ProductName="Boston Crab Meat" }
            };

            gridLookUpEdit1.Properties.DataSource = products;
            gridLookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard;
            gridLookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.True;
            gridLookUpEdit1.Properties.ValueMember = "ProductName";
            gridLookUpEdit1.Properties.DisplayMember = gridLookUpEdit1.Properties.ValueMember;
            gridLookUpEdit1.ProcessNewValue += GridLookUpEdit1_ProcessNewValue;

        }

        Dictionary<LookUpEditBase, LabelControl> labelDictionaryCore;
        Dictionary<LookUpEditBase, LabelControl> labelDictionary {
            get {
                if (labelDictionaryCore == null) {
                    labelDictionaryCore = new Dictionary<LookUpEditBase, LabelControl>();
                    labelDictionaryCore.Add(lookUpEdit1, labelControl1);
                    labelDictionaryCore.Add(gridLookUpEdit1, labelControl2);
                }
                return labelDictionaryCore;
            }
        }

        private void LookUpEdit1_EditValueChanged(object sender, EventArgs e) {
            //Display lookup editor's current value.
            LookUpEditBase lookupEditor = sender as LookUpEditBase;
            if (lookupEditor == null) return;
            LabelControl label = labelDictionary[lookupEditor];
            if (label == null) return;
            if (lookupEditor.EditValue == null)
                label.Text = "Current EditValue: null";
            else
                label.Text = "Current EditValue: " + lookupEditor.EditValue.ToString();
        }

        private void GridLookUpEdit1_ProcessNewValue(object sender, DevExpress.XtraEditors.Controls.ProcessNewValueEventArgs e) {
            //Add new values to GridLookUpEdit control's DataSource.
            GridLookUpEdit gridLookup = sender as GridLookUpEdit;
            if (e.DisplayValue == null) return;
            string newValue = e.DisplayValue.ToString();
            if (newValue == String.Empty) return;
            if (MessageBox.Show(this, "Add '" + newValue + "' to list?", "Confirm", MessageBoxButtons.YesNo) == DialogResult.Yes) {
                List<Product> ds = gridLookup.Properties.DataSource as List<Product>;
                ds.Add(new Product { ProductName = newValue });
                e.Handled = true;
            }
        }
    }

    public class Product {
        public string ProductName { get; set; }
    }

}

Imports DevExpress.XtraEditors
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Linq
Imports System.Text
Imports System.Threading.Tasks
Imports System.Windows.Forms

Namespace Lookup_ComboboxMode
    Partial Public Class Form1
        Inherits Form

        Public Sub New()
            InitializeComponent()
        End Sub

        Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
            initLookupEdit()
            initGridLookupEdit()
        End Sub

        Private Sub initLookupEdit()
            AddHandler lookUpEdit1.EditValueChanged, AddressOf LookUpEdit1_EditValueChanged

            lookUpEdit1.Properties.NullText = "(select or type value)"

            Dim colors() As String = { "Yellow", "Red", "Green", "Black", "White" }

            lookUpEdit1.Properties.DataSource = colors
            lookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard
            lookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.Default 'Default is equivalent to True for LookupEdit control
        End Sub

        Private Sub initGridLookupEdit()
            AddHandler gridLookUpEdit1.EditValueChanged, AddressOf LookUpEdit1_EditValueChanged
            gridLookUpEdit1.Properties.NullText = "(select or type value)"

            Dim products As New List(Of Product) From { _
                New Product() With {.ProductName="Chang"}, _
                New Product() With {.ProductName="Ipoh Coffee"}, _
                New Product() With {.ProductName="Ravioli Angelo"}, _
                New Product() With {.ProductName="Filo Mix"}, _
                New Product() With {.ProductName="Tunnbröd"}, _
                New Product() With {.ProductName="Konbu"}, _
                New Product() With {.ProductName="Boston Crab Meat"} _
            }

            gridLookUpEdit1.Properties.DataSource = products
            gridLookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard
            gridLookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.True
            gridLookUpEdit1.Properties.ValueMember = "ProductName"
            gridLookUpEdit1.Properties.DisplayMember = gridLookUpEdit1.Properties.ValueMember
            AddHandler gridLookUpEdit1.ProcessNewValue, AddressOf GridLookUpEdit1_ProcessNewValue

        End Sub

        Private labelDictionaryCore As Dictionary(Of LookUpEditBase, LabelControl)
        Private ReadOnly Property labelDictionary() As Dictionary(Of LookUpEditBase, LabelControl)
            Get
                If labelDictionaryCore Is Nothing Then
                    labelDictionaryCore = New Dictionary(Of LookUpEditBase, LabelControl)()
                    labelDictionaryCore.Add(lookUpEdit1, labelControl1)
                    labelDictionaryCore.Add(gridLookUpEdit1, labelControl2)
                End If
                Return labelDictionaryCore
            End Get
        End Property

        Private Sub LookUpEdit1_EditValueChanged(ByVal sender As Object, ByVal e As EventArgs)
            'Display lookup editor's current value.
            Dim lookupEditor As LookUpEditBase = TryCast(sender, LookUpEditBase)
            If lookupEditor Is Nothing Then
                Return
            End If
            Dim label As LabelControl = labelDictionary(lookupEditor)
            If label Is Nothing Then
                Return
            End If
            If lookupEditor.EditValue Is Nothing Then
                label.Text = "Current EditValue: null"
            Else
                label.Text = "Current EditValue: " & lookupEditor.EditValue.ToString()
            End If
        End Sub

        Private Sub GridLookUpEdit1_ProcessNewValue(ByVal sender As Object, ByVal e As DevExpress.XtraEditors.Controls.ProcessNewValueEventArgs)
            'Add new values to GridLookUpEdit control's DataSource.
            Dim gridLookup As GridLookUpEdit = TryCast(sender, GridLookUpEdit)
            If e.DisplayValue Is Nothing Then
                Return
            End If
            Dim newValue As String = e.DisplayValue.ToString()
            If newValue = String.Empty Then
                Return
            End If
            If MessageBox.Show(Me, "Add '" & newValue & "' to list?", "Confirm", MessageBoxButtons.YesNo) = System.Windows.Forms.DialogResult.Yes Then
                Dim ds As List(Of Product) = TryCast(gridLookup.Properties.DataSource, List(Of Product))
                ds.Add(New Product With {.ProductName = newValue})
                e.Handled = True
            End If
        End Sub
    End Class

    Public Class Product
        Public Property ProductName() As String
    End Class

End Namespace

lookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard;
    lookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.Default; //Default is equivalent to True for LookupEdit control
}

lookUpEdit1.Properties.TextEditStyle = DevExpress.XtraEditors.Controls.TextEditStyles.Standard
    lookUpEdit1.Properties.AcceptEditorTextAsNewValue = DevExpress.Utils.DefaultBoolean.Default 'Default is equivalent to True for LookupEdit control
End Sub