2026 Releases

Updated on Feb 13, 2026

This article lists the breaking or important changes in the 2026 releases of Telerik UI for ASP.NET MVC.

Telerik UI for ASP.NET MVC 2026 Q1

TreeView Enhanced Rendering (HTML and CSS)

Starting with the 2026 Q1 release, the TreeView adopts enhanced rendering that updates the generated HTML and the CSS hooks used for styling.

Key HTML Structure Changes

Wrapper class renamed

Before: Position-based wrapper classes were used:

• k-treeview-top
• k-treeview-mid
• k-treeview-bot

After: A single unified wrapper class is used:

• k-treeview-item-content

If you have custom CSS or jQuery selectors, replace selectors that target the positional classes with .k-treeview-item-content.

CSS variable for indentation level

Each .k-treeview-item now renders a --kendo-treeview-level CSS custom property that the theme uses to calculate indentation via padding-inline-start.

Example:

html

<li class="k-treeview-item" style="--kendo-treeview-level: 1;">
    ...
</li>
<li class="k-treeview-item" style="--kendo-treeview-level: 2;">
    ...
</li>

State classes moved

Before: State classes (k-hover, k-focus, k-selected, k-disabled) were applied to the .k-treeview-leaf element.

After: State classes are applied to the .k-treeview-item-content wrapper.

Update any custom selectors accordingly, for example:

css

/* Before */
.k-treeview .k-treeview-leaf.k-selected { /* ... */ }

/* After */
.k-treeview .k-treeview-item-content.k-selected { /* ... */ }

Appearance Defaults Removed

Starting with the 2026 Q1 release, Telerik UI for ASP.NET MVC components no longer render default appearance CSS classes. Previously, components automatically added size, rounded, fillMode, and themeColor classes to their HTML output. Instead, these properties now default to null, allowing the theme's CSS to control the component styling.

What Changed

Previously, components had hardcoded defaults like:

• Size = ComponentSize.Medium
• Rounded = Rounded.Medium
• FillMode = ButtonFillMode.Solid
• ThemeColor = ThemeColor.Base

Now, these properties default to null. When null, no CSS modifier classes (like k-button-md, k-rounded-md, k-button-solid) are added to the component markup. The theme's base CSS selectors control the default appearance.

Components previously rendered with explicit styling classes like:

html

<!-- Before -->
<button class="k-button k-button-md k-rounded-md k-button-solid k-button-solid-base">Click Me</button>

Now render with minimal base classes:

html

<!-- After -->
<button class="k-button">Click Me</button>

The visual appearance remains the same because Kendo Themes v13+ apply default styles to base classes.

API Changes

1. None enum value removed from appearance enums
2. Builder methods now accept nullable types for appearance properties

Removed Enum Values

The following None values have been removed from appearance enums:

Enum	Removed Value
ComponentSize	None
FillMode	None
ButtonFillMode	None
ChipFillMode	None

Migration for None Value Usage

csharp

// Before - using None to disable styling (NO LONGER VALID)
@(Html.Kendo().Button()
    .Name("btn")
    .Size(ComponentSize.None)  // Compile error!
)

// After - omit the call entirely
@(Html.Kendo().Button()
    .Name("btn")
)

Removed CSS Classes by Category

Size Classes (No Longer Rendered by Default)

Class	Component Types
k-button-sm	Buttons
k-button-md	Buttons
k-button-lg	Buttons
k-input-sm	Input components
k-input-md	Input components
k-input-lg	Input components
k-picker-sm	Picker components
k-picker-md	Picker components
k-picker-lg	Picker components
k-checkbox-sm	CheckBox, TreeView
k-checkbox-md	CheckBox, TreeView
k-checkbox-lg	CheckBox
k-chip-sm	Chip, ChipList
k-chip-md	Chip, ChipList
k-chip-lg	Chip
k-badge-sm	Badge
k-badge-md	Badge
k-badge-lg	Badge
k-avatar-sm	Avatar
k-avatar-md	Avatar
k-avatar-lg	Avatar
k-loader-sm	Loader
k-loader-md	Loader
k-loader-lg	Loader

Rounded Classes (No Longer Rendered by Default)

Class	Description
k-rounded-sm	Small border radius
k-rounded-md	Medium border radius
k-rounded-lg	Large border radius
k-rounded-full	Full/pill border radius

FillMode Classes (No Longer Rendered by Default)

Class	Component Types
k-button-solid	Buttons
k-button-solid-base	Buttons with base theme color
k-button-solid-primary	Buttons with primary theme color
k-button-flat	Flat buttons
k-button-flat-base	Flat buttons with base theme color
k-button-flat-primary	Flat buttons with primary theme color
k-button-outline	Outline buttons
k-input-solid	Input components
k-input-flat	Input components
k-input-outline	Input components
k-picker-solid	Picker components
k-picker-flat	Picker components
k-picker-outline	Picker components
k-chip-solid	Chip
k-chip-solid-base	Chip with base theme color
k-chip-outline	Chip
k-badge-solid	Badge
k-badge-outline	Badge
k-avatar-solid	Avatar
k-avatar-outline	Avatar

ThemeColor Classes (No Longer Rendered by Default)

Class Pattern	Examples
k-button-solid-{color}	k-button-solid-base, k-button-solid-primary, k-button-solid-secondary
k-button-flat-{color}	k-button-flat-base, k-button-flat-primary
k-chip-solid-{color}	k-chip-solid-base, k-chip-solid-primary
k-badge-solid-{color}	k-badge-solid-primary, k-badge-solid-secondary

Default Appearance Changes - Affected Components

The following components no longer render default appearance classes:

Input Components

Component	fillMode	size	rounded	themeColor
AutoComplete	Removed	Removed	Removed	-
ComboBox	Removed	Removed	Removed	-
DateInput	Removed	Removed	Removed	-
DatePicker	Removed	Removed	Removed	-
DateRangePicker	Removed	Removed	Removed	-
DateTimePicker	Removed	Removed	Removed	-
DropDownList	Removed	Removed	Removed	-
DropDownTree	Removed	Removed	Removed	-
MaskedTextBox	Removed	Removed	Removed	-
MultiSelect	Removed	Removed	Removed	-
NumericTextBox	Removed	Removed	Removed	-
OTPInput	Removed	Removed	Removed	-
TextArea	Removed	Removed	Removed	-
TextBox	Removed	Removed	Removed	-
TimeDurationPicker	Removed	Removed	Removed	-
TimePicker	Removed	Removed	Removed	-
ColorPicker	Removed	Removed	Removed	-
ColorGradient	-	Removed	-	-
ColorPalette	-	Removed	-	-
Signature	Removed	Removed	Removed	-

Button Components

Component	fillMode	size	rounded	themeColor
Button	Removed	Removed	Removed	Removed
ButtonGroup	Removed	-	-	-
SplitButton	Removed	Removed	Removed	Removed
DropDownButton	Removed	Removed	Removed	Removed
FloatingActionButton	Removed	Removed	Removed	Removed

Chip Components

Component	fillMode	size	rounded	themeColor
Chip	Removed	Removed	Removed	Removed
ChipList	-	Removed	-	-

Indicator Components

Component	fillMode	size	rounded	themeColor
Avatar	Removed	Removed	Removed	Removed
Badge	Removed	Removed	Removed	Removed
Loader	-	Removed	-	Removed

The default themeColor of the Badge component is now primary.

Navigation Components

Component	fillMode	size	rounded	themeColor
BottomNavigation	Removed	-	-	Removed
Breadcrumb	-	Removed	-	-
TabStrip	-	Removed	-	-

Selection Components

Component	fillMode	size	rounded	themeColor
CheckBox	-	Removed	Removed	-
RadioButton	-	Removed	-	-
Switch	-	Removed	Removed	-

Data Components

Component	fillMode	size	rounded	themeColor
Grid	-	Removed	-	-
ListBox	-	Removed	-	-
Pager	-	Removed	-	-
TreeView	-	Removed	-	-

Layout & Containers

Component	fillMode	size	rounded	themeColor
AppBar	-	-	-	Removed
Dialog	-	-	-	Removed
Window	-	-	-	Removed
ToolBar	Removed	Removed	-	-
Form	-	Removed	-	-

Notification

Starting with 2026 Q1 version when no type parameter is passed the the show method, the Notification will be displayed with default colors. Previously, the default value of the type property was info. If you need to acheive the previous behavior you can use the approaches demonstrated below:

Razor

var notification = $("#notification").data("kendoNotification");

notification.show("Some text", "info");

//or

notification.info("Some text");

Icons

Component	fillMode	size	rounded	themeColor
Icon	-	Removed	-	Removed
SVGIcon	-	Removed	-	Removed

Migration Guide

For HTML Helper (MVC)

If you need explicit styling, set the options:

csharp

// Before (implicit defaults)
@(Html.Kendo().Button()
    .Name("myButton")
    .Content("Click Me")
)
// Rendered: <button class="k-button k-button-md k-rounded-md k-button-solid k-button-solid-base">

// After (explicit sizing)
@(Html.Kendo().Button()
    .Name("myButton")
    .Content("Click Me")
    .Size(ComponentSize.Medium)
    .Rounded(Rounded.Medium)
    .FillMode(ButtonFillMode.Solid)
    .ThemeColor(ThemeColor.Base)
)
// Rendered: <button class="k-button k-button-md k-rounded-md k-button-solid k-button-solid-base">

For Tag Helpers (Core)

html

<!-- Before (implicit defaults) -->
<kendo-button name="myButton">Click Me</kendo-button>

<!-- After (explicit sizing) -->
<kendo-button name="myButton"
              size="ComponentSize.Medium"
              rounded="Rounded.Medium"
              fill-mode="ButtonFillMode.Solid"
              theme-color="ThemeColor.Base">
    Click Me
</kendo-button>

Grid Component Changes

The Grid's internal elements (toolbar, pager, buttons) also no longer render default classes:

csharp

// Before
@(Html.Kendo().Grid<Product>()
    .Name("grid")
    // Size defaulted to Medium
)

// After - Grid Size is null by default
// Set explicitly if needed:
@(Html.Kendo().Grid<Product>()
    .Name("grid")
    .Size(ComponentSize.Medium)
)

Dialog Actions

csharp

// Before
.Actions(actions =>
{
    actions.Add().Text("OK").FillMode(ButtonFillMode.None); // No longer valid
})

// After
.Actions(actions =>
{
    actions.Add().Text("OK"); // Omit FillMode for default styling
})

Custom CSS Updates

If you have custom CSS targeting size classes:

css

/* Before - targeting medium buttons */
.k-button.k-button-md {
    /* custom styles */
}

/* After - target base class (theme provides defaults) */
.k-button {
    /* custom styles */
}

/* Or explicitly set size in code and target that class */

Builder Method Signature Changes

The following builder methods now accept nullable types:

Method	Before	After
Size()	ComponentSize value	ComponentSize? value
Rounded()	Rounded value	Rounded? value
FillMode()	ButtonFillMode value	ButtonFillMode? value
ThemeColor()	ThemeColor value	ThemeColor? value

This affects all components with appearance options (Button, ComboBox, Grid, TextBox, etc.).

Theme Version Requirement

This change requires Kendo Themes v13.0.0 or later. Update your theme package references:

xml

<!-- NuGet packages -->
<PackageReference Include="Telerik.UI.for.AspNet.Core" Version="2026.1.xxx" />

Or CDN references:

html

<link rel="stylesheet" href="https://kendo.cdn.telerik.com/themes/13.0.0/default/default-main.css" />

Benefits

1. Cleaner DOM - Components render fewer CSS classes
2. Flexible Theming - Easier to customize default appearance via CSS
3. Smaller Markup - Reduced HTML output size
4. Centralized Defaults - Styling defaults managed in CSS, not server-side code

Diagram

For the fluent wrappers DashTypes were a string and are now enums.

• DiagramConnectionContentBorderSettingsBuilder
• DiagramConnectionDefaultsContentBorderSettingsBuilder
• DiagramConnectionDefaultsEndCapStrokeSettingsBuilder
• DiagramConnectionDefaultsStartCapStrokeSettingsBuilder
• DiagramConnectionEndCapStrokeSettingsBuilder
• DiagramConnectionStartCapStrokeSettingsBuilder
• DiagramEditableResizeHandlesHoverStrokeSettingsBuilder
• DiagramEditableResizeHandlesStrokeSettingsBuilder
• DiagramEditableSelectStrokeSettingsBuilder
• DiagramSelectableStrokeSettingsBuilder
• DiagramShapeDefaultsStrokeSettingsBuilder
• DiagramShapeStrokeSettingsBuilder
• DiagramStrokeSettingsBuilder