gpt-5-3-codex
GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the software engineering strength of GPT-5.2-Codex with the broader reasoning and professional knowledge of GPT-5.2.
Pricing: Input 350 credits / 1M tokens (≈ $1.75), Output 2800 credits / 1M tokens (≈ $14.00).
Prices updated
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GPT-5.3-Codex API on ModelFold
GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the software engineering strength of GPT-5.2-Codex with the broader reasoning and professional knowledge of GPT-5.2. Try GPT-5.3-Codex in the ModelFold Playground, then call it from your own code through an OpenAI-compatible chat completions API.
What Is the GPT-5.3-Codex API
GPT-5.3-Codex at a glance
GPT-5.3-Codex is a chat model from OpenAI. It accepts text, images and files (such as PDF) as input and returns text, with a context window of up to 400K tokens.
Use it without hosting anything
On ModelFold you call GPT-5.3-Codex with a single API key — no model weights to download and no inference servers to run. The same key also works for the other chat, image, video and audio models on ModelFold.
Core Capabilities of GPT-5.3-Codex
Up to 400K tokens of context
Keep long conversations, large documents and sizeable code in a single request, so the model can reason over the full material instead of fragments.
Understands images and files (such as PDF)
Besides text, GPT-5.3-Codex accepts images and files (such as PDF) as input, so a single request can combine instructions with visual or other media.
Function calling
GPT-5.3-Codex supports tool (function) calling: describe your functions in the request and the model returns structured calls your code can run — the basis for agents and integrations.
Adjustable reasoning effort
Choose a reasoning effort level (low, medium or high) per request to balance depth of thinking against speed and token usage.
Structured outputs
Ask for JSON that follows a schema (response_format), which makes extraction, classification and system integrations more reliable.
How to Use GPT-5.3-Codex on ModelFold
- 1
Step 1: Try it in the Playground
Open the Playground at the top of this page, type a prompt and see how GPT-5.3-Codex responds before writing any code.
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Step 2: Create an API key
Sign in to ModelFold and create an API key in the console. Keep it secret and send it as a Bearer token.
- 3
Step 3: Send a request
Call POST https://modelfold.ai/v1/chat/completions with "model": "gpt-5-3-codex" and your messages. Existing OpenAI-compatible SDKs work by changing the base URL and key.
- ✓
Step 4: Ship and monitor
Integrate the response into your product and check token usage and spend for every call in the console logs.
What You Can Build with GPT-5.3-Codex
AI coding assistants
Generate, explain, debug and refactor code, review pull requests and work through multi-file changes in developer tools and IDE plugins.
Autonomous agents
Build agents that plan multi-step tasks, call your tools and APIs, and keep working toward a goal across long sessions.
Security analysis
Assist with code auditing, vulnerability triage and reviewing configurations as part of security workflows.
Analysis and complex reasoning
Work through research questions, data interpretation, planning and other problems that need careful step-by-step reasoning.
Frequently Asked Questions
What is GPT-5.3-Codex?⌄
GPT-5.3-Codex is OpenAI’s most advanced agentic coding model, combining the software engineering strength of GPT-5.2-Codex with the broader reasoning and professional knowledge of GPT-5.2.
Which inputs does GPT-5.3-Codex support?⌄
GPT-5.3-Codex accepts text, images and files (such as PDF) and returns text. Through ModelFold you can send text and images (OpenAI-style image_url content); in the Playground you can also attach documents, which are converted to text.
How long is the context window of GPT-5.3-Codex?⌄
Up to 400K tokens, shared between your input and the model’s output.
Does GPT-5.3-Codex support function calling?⌄
Yes. GPT-5.3-Codex supports tools / function calling through the standard tools parameter of the chat completions API.
How is GPT-5.3-Codex billed on ModelFold?⌄
Pay as you go by tokens: input and output tokens are charged at the per-million-token prices shown on this page. There is no monthly fee, and failed requests are not charged.
How do I call GPT-5.3-Codex through the API?⌄
Send a POST request to https://modelfold.ai/v1/chat/completions with "model": "gpt-5-3-codex", using your ModelFold API key as the Bearer token.
| Input | 350 credits 1M tokens≈ $1.75 |
| Output | 2800 credits 1M tokens≈ $14.00 |
Billed per token: input and output are priced separately, and thinking tokens count as output. The Playground charges exactly the same way.
Read API docs →AI Agents · Claude Code / Cursor / Trae →curl https://modelfold.ai/v1/chat/completions \
-H "Authorization: Bearer $MODELFOLD_API_KEY" \
-H "Content-Type: application/json" \
-d '{"model":"gpt-5-3-codex","messages":[{"role":"user","content":"Hello"}]}'