GPT-5.3 Codex API
About
Build advanced reasoning agents with GPT-5.3 Codex, a specialized AI model optimized for complex logic and chain-of-thought tasks. This model delivers cost-effective pricing at $1.75/1M input and $14.00/1M output tokens, native tool calling support. Access GPT-5.3 Codex via the ZenMux API with up to 128K output tokens.
Capabilities
Input Modalities
text
Output Modalities
text
Reasoning
Yes
Structured Output
No
Tool Use
Yes
WeightsClosed
Temperature
Adjustable
Attachment
Supported
Limits
Context Window
400K
Tokens
Input Limit
400K
Tokens
Max Output
128K
Tokens
Pricing
Standard (per 1M tokens)
Input
$1.75
Output
$14.00
Frequently Asked Questions
GPT-5.3 Codex by ZenMux costs $1.75 per 1M input tokens and $14.00 per 1M output tokens.
Model Details
API Integration
NPM Package
@ai-sdk/anthropic
Environment Variables
ZENMUX_API_KEY
API Base URL
https://zenmux.ai/api/anthropic/v1