The LanguageModel interface of the Prompt API represents a session with a browser-provided language model. It exposes static methods for creating sessions and checking availability, as well as instance methods for prompting the model, appending context, and managing the context window.

LanguageModel instances cannot be constructed directly. Instead, use the static LanguageModel.create() method.

Instance properties

LanguageModel.contextUsage Read only

Returns the number of context window tokens currently consumed by this session.

LanguageModel.contextWindow Read only

Returns the total context window size available for this session, in tokens.

Static methods

LanguageModel.availability()

Returns a Promise that resolves with an enumerated value indicating whether the language model is available for the given options.

LanguageModel.create()

Returns a Promise that resolves with a new LanguageModel session, downloading the model data if necessary.

Instance methods

LanguageModel.append()

Returns a Promise that resolves when the given input has been added to the session's context window, without generating a response.

LanguageModel.clone()

Returns a Promise that resolves with a new LanguageModel session that is a copy of the session it is called on, including all context.

LanguageModel.destroy()

Releases the resources assigned to the LanguageModel instance it is called on and stops any further activity on it.

LanguageModel.measureContextUsage()

Returns a Promise that resolves with the number of context window tokens that the given input would consume if it were used in an operation such as prompt() or append().

LanguageModel.prompt()

Returns a Promise that resolves with the model's complete response to the given input.

LanguageModel.promptStreaming()

Returns a ReadableStream that streams the model's response to the given input as it is generated.

Events

contextoverflow

Fired when a prompt(), promptStreaming(), or append() call exceeds the context window size.

Examples

Creating a session and prompting the model

This example first calls create() to get a new session. It specifies that the language model adopt a "system" role and defines how it should behave. Note that the example uses await because create() returns a Promise. This may take some time to resolve if the model needs to be downloaded.

After creating the session, the example calls prompt() to ask a specific question.

const session = await LanguageModel.create({
  initialPrompts: [
    {
      role: "system",
      content: "You are a helpful assistant.",
    },
  ],
});

const response = await session.prompt("What is the capital of France?");
console.log(response); // "The capital of France is Paris."

Streaming a response

This example calls promptStreaming() to get an instance of ReadableStream and writes it to the console in chunks.

const session = await LanguageModel.create();
const readableStream = session.promptStreaming("Tell me a short story.");

for await (const chunk of readableStream) {
  console.log(chunk);
}

Specifications

Browser compatibility

See also

• Prompt API