Chat completions - Hopper

POST /v1/chat/completions generates a chat completion. See Models for model IDs and pricing. This page documents the fields Hopper defines or constrains.

Request

model (string, required) — gemma-4-31b.
messages (array, required) — Prompt and history. The context limit, including input and output, is 262,144 tokens for Gemma 4 31B.
stream (boolean, optional, default false) — Returns a Server-Sent Events stream of chat.completion.chunk objects.
tools (array, optional) — Function definitions the model may call.

The request body is limited to 10 MB; a larger body returns 413.

Streaming

On stream: true, Hopper sets stream_options.include_usage on the upstream request and removes the resulting usage chunk unless you sent that option yourself.

import os

from openai import OpenAI

client = OpenAI(
    base_url="https://api.withhopper.com/v1",
    api_key=os.environ["HOPPER_API_KEY"],
)

stream = client.chat.completions.create(
    model="gemma-4-31b",
    messages=[{"role": "user", "content": "Count to five."}],
    stream=True,
)
for chunk in stream:
    print(chunk.choices[0].delta.content or "", end="", flush=True)

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.withhopper.com/v1",
  apiKey: process.env.HOPPER_API_KEY,
});

const stream = await client.chat.completions.create({
  model: "gemma-4-31b",
  messages: [{ role: "user", content: "Count to five." }],
  stream: true,
});
for await (const chunk of stream) {
  process.stdout.write(chunk.choices[0]?.delta?.content ?? "");
}

curl -N https://api.withhopper.com/v1/chat/completions \
  -H "Authorization: Bearer $HOPPER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemma-4-31b",
    "messages": [{"role": "user", "content": "Count to five."}],
    "stream": true
  }'

Tool calling

Pass tools; when the model calls one, the response message carries tool_calls instead of content.

import os

from openai import OpenAI

client = OpenAI(
    base_url="https://api.withhopper.com/v1",
    api_key=os.environ["HOPPER_API_KEY"],
)

tools = [
    {
        "type": "function",
        "function": {
            "name": "get_balance",
            "description": "Return the account balance in dollars.",
            "parameters": {
                "type": "object",
                "properties": {"account_id": {"type": "string"}},
                "required": ["account_id"],
            },
        },
    }
]

response = client.chat.completions.create(
    model="gemma-4-31b",
    messages=[{"role": "user", "content": "What is the balance on account a-17?"}],
    tools=tools,
)
print(response.choices[0].message.tool_calls)

import OpenAI from "openai";

const client = new OpenAI({
  baseURL: "https://api.withhopper.com/v1",
  apiKey: process.env.HOPPER_API_KEY,
});

const tools = [
  {
    type: "function" as const,
    function: {
      name: "get_balance",
      description: "Return the account balance in dollars.",
      parameters: {
        type: "object",
        properties: { account_id: { type: "string" } },
        required: ["account_id"],
      },
    },
  },
];

const response = await client.chat.completions.create({
  model: "gemma-4-31b",
  messages: [{ role: "user", content: "What is the balance on account a-17?" }],
  tools,
});
console.log(response.choices[0].message.tool_calls);

curl https://api.withhopper.com/v1/chat/completions \
  -H "Authorization: Bearer $HOPPER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gemma-4-31b",
    "messages": [{"role": "user", "content": "What is the balance on account a-17?"}],
    "tools": [{
      "type": "function",
      "function": {
        "name": "get_balance",
        "description": "Return the account balance in dollars.",
        "parameters": {
          "type": "object",
          "properties": {"account_id": {"type": "string"}},
          "required": ["account_id"]
        }
      }
    }]
  }'

Send the tool result back as a tool message with the matching tool_call_id to continue the conversation. Error codes are listed in Errors.