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HeyGen Avatar Rendering Engines

HeyGen has three avatar rendering engines, all available on the v3 API and selected per request through the engine field on POST /v3/videos. New integrations should default to Avatar IV for broad coverage, opt into Avatar V for the highest-fidelity motion and lip-sync, and use Avatar III for its dedicated photo-to-video pipeline. 
{
  "type": "avatar",
  "avatar_id": "YOUR_LOOK_ID",
  "script": "Hello from HeyGen.",
  "voice_id": "YOUR_VOICE_ID",
  "engine": { "type": "avatar_iv" }
}
Before requesting Avatar V, confirm the avatar look supports it by checking supported_api_engines on the look (GET /v3/avatars/looks/{look_id}) — requesting it for a look that doesn’t list it returns a 400 error. Avatar III does not appear in supported_api_engines; it accepts any avatar look shown in the table below.

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Choosing an engine

Avatar VAvatar IVAvatar III
engine.typeavatar_vavatar_ivavatar_iii
API versionv3v3v3
Default engine✗ (explicit opt-in)✓✗ (explicit opt-in)
Available to new users✓✓✓
Digital Twin✓✓✓
Photo Avatar✗✓✓ (dedicated pipeline)
Studio Avatar✗✓✓ (renders as Digital Twin)
Arbitrary image input✗✓✗
motion_prompt✓✓✗
expressiveness✗✓✗
Cross-reference animation✓✗✗
4K output✗✗✓ (except Photo Avatar)
Eligibility check required✓✗✗
A separate, older Avatar III engine remains available to existing customers through the legacy v1/v2 endpoints. It uses a different pipeline and is not the same as the Avatar III (avatar_iii) engine documented here. It is not offered on the new developer platform. See Avatar III for the distinction.