GPT-5.3 Codex vs Claude 3 Opus

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. Intelligence & Reasoning

• Highest capability in the Claude 3 family
• Near-human comprehension and fluency
• Excels at MMLU, GPQA, GSM8K, advanced reasoning tasks

2. Complex Problem Solving

• Best for research, strategy, multi-step planning
• Handles ambiguous, open-ended tasks with ease

3. Vision & Multimodal Capabilities

• Strong chart/graph understanding
• Processes documents, technical diagrams, and dense visual data

4. Recall & Long-Context Reasoning

• Near-perfect recall (>99% on NIAH benchmark)
• Handles very large documents and multi-file workflows

5. Enterprise-Grade Accuracy

• Significantly reduced hallucinations
• High correctness rate for factual queries