# AI21 Labs Jurassic-2 models
<a name="model-parameters-jurassic2"></a>

This section provides inference parameters and a code example for using AI21 Labs AI21 Labs Jurassic-2 models.

**Topics**
+ [Inference parameters](#model-parameters-jurassic2-request-response)
+ [Code example](#api-inference-examples-a2i-jurassic)

## Inference parameters
<a name="model-parameters-jurassic2-request-response"></a>

The AI21 Labs Jurassic-2 models support the following inference parameters.

**Topics**
+ [Randomness and Diversity](#model-parameters-jurassic2-random)
+ [Length](#model-parameters-jurassic2-length)
+ [Repetitions](#model-parameters-jurassic2-reps)
+ [Model invocation request body field](#model-parameters-jurassic2-request-body)
+ [Model invocation response body field](#model-parameters-jurassic2-response-body)

### Randomness and Diversity
<a name="model-parameters-jurassic2-random"></a>

The AI21 Labs Jurassic-2 models support the following parameters to control randomness and diversity in the response.
+ **Temperature** (`temperature`)– Use a lower value to decrease randomness in the response.
+ **Top P** (`topP`) – Use a lower value to ignore less probable options.

### Length
<a name="model-parameters-jurassic2-length"></a>

The AI21 Labs Jurassic-2 models support the following parameters to control the length of the generated response.
+ **Max completion length** (`maxTokens`) – Specify the maximum number of tokens to use in the generated response.
+ **Stop sequences** (`stopSequences`) – Configure stop sequences that the model recognizes and after which it stops generating further tokens. Press the Enter key to insert a newline character in a stop sequence. Use the Tab key to finish inserting a stop sequence.

### Repetitions
<a name="model-parameters-jurassic2-reps"></a>

The AI21 Labs Jurassic-2 models support the following parameters to control repetition in the generated response.
+ **Presence penalty** (`presencePenalty`) – Use a higher value to lower the probability of generating new tokens that already appear at least once in the prompt or in the completion.
+ **Count penalty** (`countPenalty`) – Use a higher value to lower the probability of generating new tokens that already appear at least once in the prompt or in the completion. Proportional to the number of appearances.
+ **Frequency penalty** (`frequencyPenalty`) – Use a high value to lower the probability of generating new tokens that already appear at least once in the prompt or in the completion. The value is proportional to the frequency of the token appearances (normalized to text length).
+ **Penalize special tokens** – Reduce the probability of repetition of special characters. The default values are `true`.
  + **Whitespaces** (`applyToWhitespaces`) – A `true` value applies the penalty to whitespaces and new lines.
  + **Punctuations** (`applyToPunctuation`) – A `true` value applies the penalty to punctuation.
  + **Numbers** (`applyToNumbers`) – A `true` value applies the penalty to numbers.
  + **Stop words** (`applyToStopwords`) – A `true` value applies the penalty to stop words.
  + **Emojis** (`applyToEmojis`) – A `true` value excludes emojis from the penalty.

### Model invocation request body field
<a name="model-parameters-jurassic2-request-body"></a>

When you make an [InvokeModel](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_InvokeModel.html) or [InvokeModelWithResponseStream](https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_InvokeModelWithResponseStream.html) call using an AI21 Labs model, fill the `body` field with a JSON object that conforms to the one below. Enter the prompt in the `prompt` field.

```
{
    "prompt": string,
    "temperature": float,
    "topP": float,
    "maxTokens": int,
    "stopSequences": [string],
    "countPenalty": {
        "scale": float
    },
    "presencePenalty": {
        "scale": float
    },
    "frequencyPenalty": {
        "scale": float
    }
}
```

To penalize special tokens, add those fields to any of the penalty objects. For example, you can modify the `countPenalty` field as follows.

```
"countPenalty": {
    "scale": float,
    "applyToWhitespaces": boolean,
    "applyToPunctuations": boolean,
    "applyToNumbers": boolean,
    "applyToStopwords": boolean,
    "applyToEmojis": boolean
}
```

The following table shows the minimum, maximum, and default values for the numerical parameters.


****  
[\[See the AWS documentation website for more details\]](http://docs.aws.amazon.com/bedrock/latest/userguide/model-parameters-jurassic2.html)

### Model invocation response body field
<a name="model-parameters-jurassic2-response-body"></a>

For information about the format of the `body` field in the response, see [https://docs.ai21.com/reference/j2-complete-api-ref](https://docs.ai21.com/reference/j2-complete-api-ref).

**Note**  
Amazon Bedrock returns the response identifier (`id`) as an integer value.

## Code example
<a name="api-inference-examples-a2i-jurassic"></a>

This examples shows how to call the *A2I AI21 Labs Jurassic-2 Mid* model.

```
import boto3
import json

brt = boto3.client(service_name='bedrock-runtime')

body = json.dumps({
    "prompt": "Translate to spanish: 'Amazon Bedrock is the easiest way to build and scale generative AI applications with base models (FMs)'.", 
    "maxTokens": 200,
    "temperature": 0.5,
    "topP": 0.5
})

modelId = 'ai21.j2-mid-v1'
accept = 'application/json'
contentType = 'application/json'

response = brt.invoke_model(
    body=body, 
    modelId=modelId, 
    accept=accept, 
    contentType=contentType
)

response_body = json.loads(response.get('body').read())

# text
print(response_body.get('completions')[0].get('data').get('text'))
```