GPT-5.3 Codex vs GPT-5 Nano

1. Strongest Codex Model for Agentic Engineering

• OpenAI positions GPT-5.3 Codex as its most capable agentic coding model to date.
• Built for long-horizon software engineering tasks that require planning, iteration, and reliable code transformation across files.

2. Configurable Reasoning + Multimodal Input

• Supports configurable reasoning effort from low to xhigh so teams can trade off depth against latency.
• Accepts both text and image inputs while producing text output.

3. Large Context for Real Codebases

• 400 k token context window helps it work across larger repositories, implementation plans, and supporting documentation.
• Allows up to 128 k output tokens for longer code generations, patches, and technical write-ups.

4. Current Knowledge for Modern Dev Workflows

• Knowledge cut-off of Aug 31 2025 keeps it aligned with newer frameworks, libraries, and tooling.
• Supports streaming, function calling, and structured outputs for agent-style coding workflows.

1. Extremely fast performance

• Fastest model in the GPT-5 family.
• Great for real-time workflows, rapid responses, and high-throughput systems.

2. Most cost-efficient GPT-5 model

• Lowest input and output token costs.
• Suitable for large-scale or budget-sensitive applications.

3. Ideal for lightweight, well-scoped tasks

• Excels at summarization, classification, text extraction, and simple logic tasks.
• Best used when tasks are narrow and well-defined.

4. Multimodal input

• Accepts text + image as input.
• Outputs text only.

5. Broad tool support

• Supports Web Search, File Search, Image Generation (as a tool), Code Interpreter, and MCP.
• (Does not support Computer Use.)