Short answer: every IAB standard display size, plus the full video family. Here's the list.
Display (HTML5 banners)
All IAB standard sizes, selectable per pack in Ad Builder: 970×250, 728×90, 336×280, 320×480, 320×50, 300×250, 300×50, 300×600, 250×250, 160×600 — plus custom sizes when a placement needs something unusual.
Video
CTV — 1920×1080 connected-TV spots (15s / 30s)
OLV — online video for pre-roll/mid-roll, horizontal and vertical variants
L-Bar / Squeezeback — content shrinks into a branded L-frame
Overlay — branded layer over video
Pause ads — shown when a viewer pauses streaming content
Exact specs, always current
The Creative Specs page (your name menu → Creative Specs) is generated from the live renderer: per-network media windows, copy character guidelines, caption-line trade-offs, durations, and file requirements — exportable as PDF. Details: Creative Specs — Live Format Reference.
Related