GPT-5.1 Chat

OpenAI Generally Available

GPT-5.1 Chat (AKA Instant is the fast, lightweight member of the 5.1 family, optimized for low-latency chat while retaining strong general intelligence. It uses adaptive reasoning to selectively “think” on...

Context

128K

tokens

Input

$1.25

per MTok

Output

$10.00

per MTok

Model Page

About

Modalities

Input

file Vision Text

Output

Text

Code Examples

curl https://api.openai.com/v1/chat/completions \
  -H "Authorization: Bearer $OPENAI_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "gpt-5.1-chat",
    "messages": [
      { "role": "user", "content": "Explain quantum entanglement in one sentence." }
    ]
  }'

from openai import OpenAI

client = OpenAI(
    base_url="https://api.openai.com/v1",
    api_key=os.environ["OPENAI_API_KEY"],
)
response = client.chat.completions.create(
    model="gpt-5.1-chat",
    messages=[
        {"role": "user", "content": "Explain quantum entanglement in one sentence."},
    ],
)
print(response.choices[0].message.content)

import OpenAI from "openai";

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

const response = await client.chat.completions.create({
  model: "gpt-5.1-chat",
  messages: [
    { role: "user", content: "Explain quantum entanglement in one sentence." },
  ],
});
console.log(response.choices[0].message.content);

API Parameters

Name	Type	Default	Description
`max_completion_tokens`	integer	—	Maximum number of tokens the model may generate in the response.
`max_tokens` deprecated	integer	—	Deprecated. Use max_completion_tokens.
`response_format`	one of	—	Constrain output to a JSON schema or an enum (structured outputs).
`seed`	integer	—	Deterministic seed for sampling. Same seed + same prompt produces identical output.
`structured_outputs`	boolean	—	Enable JSON-schema-constrained output.
`tool_choice`	one of	—	Controls which (if any) tool is called: "none", "auto", "required", or a specific tool.
`tools`	array	—	List of tools (functions) the model may call.

Standard OpenAI-compatible parameters. Consult the provider docs for model-specific behaviour.