# Expression 2

URL: https://docs.bithuman.ai/models/expression-2

> Expression 2 renders any character from one portrait: the whole scene generated live from the audio, on the device or in the bitHuman cloud.

## What it is

**Expression 2** (`expression-2`) generates the whole avatar scene live from the
audio — expressions, mouth and head movement are synthesized each session, not
replayed from a base video. It animates the **entire 416x720 frame** with no
face detector or cropping step, so it works for any character: cartoons,
animals, creatures, robots, and people.

At creation the platform trains a **small model of your specific identity** from
one photo. That per-identity model is what serves your sessions, and it is why
creation takes a couple of hours.

## When to choose it

- **Your character is not a photorealistic human** — this is the model for it,
  and where `model: "auto"` routes such inputs.
- **You want motion generated from the audio itself**, not patched onto a base
  video.
- **You only have a photo** — one image is enough.

For a photorealistic person animated from their own footage, compare
[Essence 2](https://docs.bithuman.ai/models/essence-2). The side-by-side is on [Models](https://docs.bithuman.ai/models).

## Where it runs

| Where | Expression 2 | How |
|---|---|---|
| [iPhone and iPad](https://docs.bithuman.ai/platforms/ios) | Yes | Swift package, `Expression2` |
| [Mac](https://docs.bithuman.ai/platforms/macos) | Yes | Swift package (macOS 13), CLI, Python |
| [Android](https://docs.bithuman.ai/platforms/android) | Yes | `expression2-android` |
| [Linux, no GPU](https://docs.bithuman.ai/deploy/cpu) | Yes | CLI, Python |
| [Browser (WebGPU)](https://docs.bithuman.ai/platforms/web) | Yes | `render=local` |
| [Your servers](https://docs.bithuman.ai/deploy/self-hosted) | Yes | CLI, Python, LiveKit plugin |
| [bitHuman cloud](https://docs.bithuman.ai/deploy/cloud) | Yes | web embed, REST API, LiveKit |
| [Fully offline](https://docs.bithuman.ai/deploy/offline) | — | Coming later |

Complete apps: [iOS Expression 2](https://docs.bithuman.ai/examples/ios-expression-2), [macOS Expression 2](https://docs.bithuman.ai/examples/macos-expression-2) and [Android Expression 2](https://docs.bithuman.ai/examples/android-expression-2).

The file you download from
[`GET /v1/agent/{code}/model/download?model=expression-2`](https://docs.bithuman.ai/api/agents#download-an-agents-model)
or `bithuman pull <CODE>` is labelled `<CODE>.imx`; `.avatar` is the legacy
extension for the same container. How fast it renders on each device is on
[performance](https://docs.bithuman.ai/performance).

## How creation works

Create the agent with [`POST /v1/agent/generate`](https://docs.bithuman.ai/api/agents#generate-an-agent)
and `model: "expression-2"`, or add `expression-2` to an existing agent with
[`POST /v1/agent/{code}/models`](https://docs.bithuman.ai/api/agents#add-a-model-to-an-existing-agent).

- **The input is a portrait image**, of any subject. Without one, the platform
  generates a portrait from your prompt first. It also generates the agent's
  10-second idle clip and prepares a voice.
- **Training takes about 2 to 2.5 hours;** an identity that needs more work gets more, so up to 4 hours is normal. Poll [`GET /v1/agent/status/{agent_id}`](https://docs.bithuman.ai/api/agents#poll-status) until `ready` or `failed`, or wait for the completion email.
- **A run that fails is refunded;** a completed creation is not, so a second `generate` is a second charge ([failure modes](https://docs.bithuman.ai/api/agents#errors)).

The creation cost is on [pricing](https://docs.bithuman.ai/pricing).

## Serving tiers

Every published configuration, including a desktop CPU with no GPU, renders faster than real time ([performance](https://docs.bithuman.ai/performance)). In the bitHuman cloud, the service picks the hardware for each session; to benchmark one tier, see [pin a tier for a benchmark](https://docs.bithuman.ai/performance#pin-a-tier-for-a-benchmark).

## Idle and speaking behavior

During silences the avatar plays its **10-second idle clip**, generated from the
identity at creation, looping forward-only without a seam. When speech starts,
the engine hands off to generated frames with a per-identity color match, so the
two stay visually continuous; idle resumes only after sustained silence, not in
pauses inside a sentence. A running session bills talking and idle time alike ([pricing](https://docs.bithuman.ai/pricing)).

**Speech onset.** The engine renders in fixed audio chunks; the moving idle
clip covers the start of each reply.

## Limits and expectations

- **Output is the full 416×720 scene**, playing at 20 frames a second.
- **A clear, frontal, well-lit photo** gives the best result. The identity is
  fixed at creation — to change the face, create a new agent.
- **The first session on a new agent** can take longer to connect while its
  model is provisioned; later sessions reuse it.
- **Before training completes**, a launch that requests this model is refused
  with [`409 MODEL_NOT_GENERATED`](https://docs.bithuman.ai/api/errors#model-errors). Once ready,
  `expression-2` appears in the agent's `supported_models`.

## Next steps

- [Models](https://docs.bithuman.ai/models) — the four models side by side
- [Agents API](https://docs.bithuman.ai/api/agents) — create, poll, download
- [Embed widget](https://docs.bithuman.ai/api/embedding) — a live session in minutes
- [Video API](https://docs.bithuman.ai/api/video) — render an MP4 with `model: "expression-2"`
- [Session behavior & troubleshooting](https://docs.bithuman.ai/resources/troubleshooting)