GPT-5.3 Chat is an update to ChatGPT's most-used model that makes everyday conversations smoother, more useful, and more directly helpful. It delivers more accurate answers with better contextualization and significantly reduces unnecessary refusals, caveats, and overly cautious phrasing that can interrupt conversational flow.
Modalities
Input Price
$1.75per 1M
Output Price
$14per 1M
Context
128K
Weekly Tokens
8.55B
Released
Mar 3, 2026
Create an API key from your OpenRouter dashboard and set it as an environment variable:
Use openai/gpt-5.3-chat with the OpenRouter API:
OpenRouter provides an OpenAI-compatible completion API to 400+ models & providers that you can call directly, or using the OpenAI SDK. Additionally, some third-party SDKs are available.
In the examples below, the OpenRouter-specific headers are optional. Setting them allows your app to appear on the OpenRouter leaderboards.
For information about using third-party SDKs and frameworks with OpenRouter, please see our frameworks documentation.
Add "stream": true to your request body to receive responses as server-sent events:
https://openrouter.ai/api/v1/chat/completionsBearer $OPENROUTER_API_KEYapplication/jsonoptional — your site URL, for rankingsoptional — your site name, for rankingsopenai/gpt-5.3-chat| Name | Type | Default | Description |
|---|---|---|---|
max_completion_tokens | integer | — | This sets the upper limit for the number of tokens the model can generate in response. |
seed | integer | — | If specified, the inferencing will sample deterministically, such that repeated requests with the same seed and parameters should return the same result. |
response_format | map | — | Forces the model to produce specific output format. |
tools | array | — | Tool calling parameter, following OpenAI's tool calling request shape. |
tool_choice | string or object | — | Controls which (if any) tool is called by the model. |