gpt-5.3-codex

Integration & capabilities

Supported protocols

curl -X POST https://api.openmodel.ai/v1/responses \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer $API_KEY" \
  -d '{
    "model": "gpt-5.3-codex",
    "input": "Hello"
  }'

Supported capabilities

Function Calling

Function calling (also known as tool calling) provides a powerful and flexible way for models to interface with external systems and access data outside their training data.

Parallel Function Calling

The model may choose to call multiple functions in a single turn.

Tool Choice

By default the model will determine when and how many tools to use. You can force specific behavior with the tool_choice parameter.

Structured Outputs

Ensures the model will always generate responses that adhere to your supplied JSON Schema.

Streaming

Lets you start printing or processing the beginning of the model's output while it continues generating the full response.

Reasoning

Reasoning models use internal reasoning tokens before producing a response.

Prompt Caching

Optimizes API usage by allowing resuming from specific prefixes in your prompts. This significantly reduces processing time and costs for repetitive tasks or prompts with consistent elements.

Vision

Models can process image inputs and analyze them — a capability known as vision.

PDF Input

Ask the model about any text, pictures, charts, and tables in PDFs you provide.

Web Search

Allows models to access up-to-date information from the internet and provide answers with sourced citations.

Context & limits