diff --git a/src/browser/Terminal.ts b/src/browser/Terminal.ts
index f0ce4694..71998bd5 100644
--- a/src/browser/Terminal.ts
+++ b/src/browser/Terminal.ts
@@ -920,7 +920,7 @@ export class Terminal extends CoreTerminal implements ITerminal {
     return this.buffer.markers;
   }
 
-  public addMarker(cursorYOffset: number): IMarker {
+  public registerMarker(cursorYOffset: number): IMarker {
     return this.buffer.addMarker(this.buffer.ybase + this.buffer.y + cursorYOffset);
   }
 
diff --git a/src/browser/TestUtils.test.ts b/src/browser/TestUtils.test.ts
index 5981a6b5..7b464a33 100644
--- a/src/browser/TestUtils.test.ts
+++ b/src/browser/TestUtils.test.ts
@@ -52,7 +52,7 @@ export class MockTerminal implements ITerminal {
   public coreService!: ICoreService;
   public optionsService!: IOptionsService;
   public unicodeService!: IUnicodeService;
-  public addMarker(cursorYOffset: number): IMarker {
+  public registerMarker(cursorYOffset: number): IMarker {
     throw new Error('Method not implemented.');
   }
   public selectLines(start: number, end: number): void {
diff --git a/src/browser/Types.d.ts b/src/browser/Types.d.ts
index d32b6099..776790cd 100644
--- a/src/browser/Types.d.ts
+++ b/src/browser/Types.d.ts
@@ -3,15 +3,19 @@
  * @license MIT
  */
 
-import { IDecorationOptions, IDecoration, IDisposable, IMarker } from 'xterm';
+import { IDecorationOptions, IDecoration, IDisposable, IMarker, Terminal as ITerminalApi } from 'xterm';
 import { IEvent } from 'common/EventEmitter';
 import { ICoreTerminal, CharData, ITerminalOptions, IColor } from 'common/Types';
 import { IMouseService, IRenderService } from './services/Services';
 import { IBuffer } from 'common/buffer/Types';
 import { IFunctionIdentifier, IParams } from 'common/parser/Types';
 
-export interface ITerminal extends IPublicTerminal, ICoreTerminal {
-  element: HTMLElement | undefined;
+/**
+ * A portion of the public API that are implemented identially internally and simply passed through.
+ */
+type InternalPassthroughApis = Omit<ITerminalApi, 'buffer' | 'parser' | 'unicode' | 'modes' | 'writeln' | 'loadAddon'>;
+
+export interface ITerminal extends InternalPassthroughApis, ICoreTerminal {
   screenElement: HTMLElement | undefined;
   browser: IBrowser;
   buffer: IBuffer;
@@ -28,78 +32,6 @@ export interface ITerminal extends IPublicTerminal, ICoreTerminal {
   cancel(ev: Event, force?: boolean): boolean | void;
 }
 
-// Portions of the public API that are required by the internal Terminal
-export interface IPublicTerminal extends IDisposable {
-  textarea: HTMLTextAreaElement | undefined;
-  rows: number;
-  cols: number;
-  buffer: IBuffer;
-  markers: IMarker[];
-  onCursorMove: IEvent<void>;
-  onData: IEvent<string>;
-  onBinary: IEvent<string>;
-  onKey: IEvent<{ key: string, domEvent: KeyboardEvent }>;
-  onLineFeed: IEvent<void>;
-  onScroll: IEvent<number>;
-  onSelectionChange: IEvent<void>;
-  onRender: IEvent<{ start: number, end: number }>;
-  onResize: IEvent<{ cols: number, rows: number }>;
-  onWriteParsed: IEvent<void>;
-  onTitleChange: IEvent<string>;
-  onBell: IEvent<void>;
-  blur(): void;
-  focus(): void;
-  resize(columns: number, rows: number): void;
-  open(parent: HTMLElement): void;
-  attachCustomKeyEventHandler(customKeyEventHandler: (event: KeyboardEvent) => boolean): void;
-  registerCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean | Promise<boolean>): IDisposable;
-  registerDcsHandler(id: IFunctionIdentifier, callback: (data: string, param: IParams) => boolean | Promise<boolean>): IDisposable;
-  registerEscHandler(id: IFunctionIdentifier, callback: () => boolean | Promise<boolean>): IDisposable;
-  registerOscHandler(ident: number, callback: (data: string) => boolean | Promise<boolean>): IDisposable;
-  registerLinkProvider(linkProvider: ILinkProvider): IDisposable;
-  registerCharacterJoiner(handler: (text: string) => [number, number][]): number;
-  deregisterCharacterJoiner(joinerId: number): void;
-  addMarker(cursorYOffset: number): IMarker;
-  registerDecoration(decorationOptions: IDecorationOptions): IDecoration | undefined;
-  hasSelection(): boolean;
-  getSelection(): string;
-  getSelectionPosition(): IBufferRange | undefined;
-  clearSelection(): void;
-  select(column: number, row: number, length: number): void;
-  selectAll(): void;
-  selectLines(start: number, end: number): void;
-  dispose(): void;
-  /**
-   * Scroll the display of the terminal
-   * @param amount The number of lines to scroll down (negative scroll up).
-   */
-  scrollLines(amount: number): void;
-  /**
-   * Scroll the display of the terminal by a number of pages.
-   * @param pageCount The number of pages to scroll (negative scrolls up).
-   */
-  scrollPages(pageCount: number): void;
-  /**
-   * Scrolls the display of the terminal to the top.
-   */
-  scrollToTop(): void;
-  /**
-   * Scrolls the display of the terminal to the bottom.
-   */
-  scrollToBottom(): void;
-  /**
-   * Scrolls to a line within the buffer.
-   * @param line The 0-based line index to scroll to.
-   */
-  scrollToLine(line: number): void;
-  clear(): void;
-  write(data: string | Uint8Array, callback?: () => void): void;
-  paste(data: string): void;
-  refresh(start: number, end: number): void;
-  clearTextureAtlas(): void;
-  reset(): void;
-}
-
 export type CustomKeyEventHandler = (event: KeyboardEvent) => boolean;
 
 export type LineData = CharData[];
diff --git a/src/browser/public/Terminal.ts b/src/browser/public/Terminal.ts
index 7a94356b..77f8fdde 100644
--- a/src/browser/public/Terminal.ts
+++ b/src/browser/public/Terminal.ts
@@ -161,7 +161,7 @@ export class Terminal extends Disposable implements ITerminalApi {
   }
   public registerMarker(cursorYOffset: number = 0): IMarker {
     this._verifyIntegers(cursorYOffset);
-    return this._core.addMarker(cursorYOffset);
+    return this._core.registerMarker(cursorYOffset);
   }
   public registerDecoration(decorationOptions: IDecorationOptions): IDecoration | undefined {
     this._checkProposedApi();
diff --git a/src/common/Types.d.ts b/src/common/Types.d.ts
index fceb4e8e..ca9e25ff 100644
--- a/src/common/Types.d.ts
+++ b/src/common/Types.d.ts
@@ -17,7 +17,7 @@ export interface ICoreTerminal {
   optionsService: IOptionsService;
   unicodeService: IUnicodeService;
   buffers: IBufferSet;
-  options: ITerminalOptions;
+  options: Required<ITerminalOptions>;
   registerCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean | Promise<boolean>): IDisposable;
   registerDcsHandler(id: IFunctionIdentifier, callback: (data: string, param: IParams) => boolean | Promise<boolean>): IDisposable;
   registerEscHandler(id: IFunctionIdentifier, callback: () => boolean | Promise<boolean>): IDisposable;
diff --git a/src/headless/Terminal.ts b/src/headless/Terminal.ts
index 2c244f21..73bcbe13 100644
--- a/src/headless/Terminal.ts
+++ b/src/headless/Terminal.ts
@@ -24,7 +24,7 @@
 import { DEFAULT_ATTR_DATA } from 'common/buffer/BufferLine';
 import { IBuffer } from 'common/buffer/Types';
 import { CoreTerminal } from 'common/CoreTerminal';
-import { EventEmitter, forwardEvent, IEvent } from 'common/EventEmitter';
+import { EventEmitter, forwardEvent } from 'common/EventEmitter';
 import { ITerminalOptions as IInitializedTerminalOptions } from 'common/services/Services';
 import { IMarker, ITerminalOptions, ScrollSource } from 'common/Types';
 
diff --git a/src/headless/Types.d.ts b/src/headless/Types.d.ts
deleted file mode 100644
index 868e5c17..00000000
--- a/src/headless/Types.d.ts
+++ /dev/null
@@ -1,31 +0,0 @@
-import { IBuffer, IBufferSet } from 'common/buffer/Types';
-import { IEvent } from 'common/EventEmitter';
-import { IFunctionIdentifier, IParams } from 'common/parser/Types';
-import { ICoreTerminal, IDisposable, IMarker, ITerminalOptions } from 'common/Types';
-
-export interface ITerminal extends ICoreTerminal {
-  rows: number;
-  cols: number;
-  buffer: IBuffer;
-  buffers: IBufferSet;
-  markers: IMarker[];
-  // TODO: We should remove options once components adopt optionsService
-  options: ITerminalOptions;
-
-  onCursorMove: IEvent<void>;
-  onData: IEvent<string>;
-  onBinary: IEvent<string>;
-  onLineFeed: IEvent<void>;
-  onResize: IEvent<{ cols: number, rows: number }>;
-  onTitleChange: IEvent<string>;
-  resize(columns: number, rows: number): void;
-  addCsiHandler(id: IFunctionIdentifier, callback: (params: IParams) => boolean): IDisposable;
-  addDcsHandler(id: IFunctionIdentifier, callback: (data: string, param: IParams) => boolean): IDisposable;
-  addEscHandler(id: IFunctionIdentifier, callback: () => boolean): IDisposable;
-  addOscHandler(ident: number, callback: (data: string) => boolean): IDisposable;
-  addMarker(cursorYOffset: number): IMarker | undefined;
-  dispose(): void;
-  clear(): void;
-  write(data: string | Uint8Array, callback?: () => void): void;
-  reset(): void;
-}