First generation

Essence 1 and Expression 1: what each is, where it runs, and its file.

Both first-generation models are maintained, not deprecated. For new work, start on Essence 2 (a photoreal person) or Expression 2 (any character).

	Essence 1	Expression 1
Renders	a pre-built identity from an `.imx` file	facial motion generated from a portrait at runtime
Where it runs	the bitHuman cloud; Python and the CLI on macOS and Linux; the browser (`render=local`)	the bitHuman cloud only
`model` value	`essence-1`	`expression-1`
Subject	a real person’s face	a real person’s face

Both need a clear photo of a real human face. A cartoon, animal, robot or creature, or a photo with no face found, is refused with 422 MODEL_SUBJECT_MISMATCH before anything is charged; for a character, use Expression 2. See Choosing a model.

Essence 1

Essence 1 (essence-1) reads a pre-built identity out of an .imx file, plays its base motion, and patches the mouth in real time to match 16 kHz mono audio, at 25 fps. It runs on a CPU, with no GPU or accelerator, and supports custom gestures. ?model=essence-1 serves it.

Where Essence 1 runs

In the bitHuman cloud, and on your own hardware through:

Python: pip install bithuman opens an Essence 1 .imx with no extra; see Python.
The CLI: bithuman run on macOS (Apple silicon) and Linux x86_64 and arm64; see CLI. render does not take Essence 1: use the Python SDK or the Talking video API for a file.
The browser: ?render=local.

Essence 1 is not in the Android SDK or the Swift package. On phones, use Essence 2 or Expression 2, or run Essence 1 from the cloud API, or from Python or the CLI on a desktop. The full matrix is on Compare models.

The Essence 1 file

One file, <CODE>.imx: the identity, and optionally baked-in idle and gesture clips. Download it with bithuman pull <CODE> --model essence-1, or:

curl -L -o "<CODE>.imx" -H "api-secret: $BITHUMAN_API_SECRET" \
  "https://api.bithuman.ai/v1/agent/<CODE>/model/download?model=essence-1"

Expression 1

Expression 1 (expression-1) animates a face from a portrait image at runtime: you give it audio, and it generates the facial motion to match, with no per-identity build step. ?model=expression-1 serves it, and it is what /v1/agent/generate creates when the request names no model.

It is a different engine from Expression 2, not an earlier version of it.

Where Expression 1 runs

In the bitHuman cloud only, on cloud GPUs. There is no CPU, Apple, Android or browser build. For an expressive model on a Mac, a phone or in a browser, use Expression 2.

Cloud output is 512×512. Expression 1 can also animate a photo with no agent: see Cloud avatar in your room.

The Expression 1 file

Usually there is nothing to download: Expression 1 renders from the agent’s portrait, so the download endpoint answers 400 MODEL_NOT_DOWNLOADABLE for most agents. A few older agents have a downloadable .imx, which the endpoint serves. The engine weights are not part of any download.

Pricing

Rates for both models are on Pricing and credits.

Older names

Older names you may meet in links, logs or files: Renamed and retired names.