GPT-OSS 20B vs o3

• Open-weight / Apache 2.0 licensed: you can use, modify, and deploy freely (commercially & academically) under permissive terms.
• Large model size (≈ 21B parameters) with Mixture-of-Experts (MoE) architecture: only ~3.6B parameters active per token, yielding efficient inference.
• Very long context window support: up to ~128 K tokens (or ~131 K tokens per some sources) enabling in-depth reasoning, long documents, or multi-turn context.
• Adjustable reasoning effort: you can trade latency vs quality by tuning “reasoning effort” levels.
• Efficient hardware requirements (for its class): designed to run on a single 16 GB-class GPU or optimized local deployments for lower latency applications.
• Strong for tasks such as reasoning, tool-use, structured output, chain-of-thought debugging: because the model is open and you can inspect its chain of thought.
• Flexibility: since weights are available, you can self-host, fine-tune, or deploy offline, giving more control than closed API models.

1. Advanced reasoning capability

• Designed for multi-step thinking across text, code, and visual inputs.
• Excels at math, science, logic puzzles, and complex analytical workflows.

2. Strong performance across domains

• Highly capable in technical writing, data analysis, and structured problem-solving.
• Useful for research, engineering tasks, and intricate instruction-following.

3. Visual reasoning support

• Accepts image inputs, enabling tasks such as diagram analysis, chart interpretation, and visual logic assessments.

4. High output capacity

• Up to 100,000 output tokens, supporting long-form content, technical breakdowns, and multi-part solutions.

5. Excellent instruction following

• Produces detailed, step-by-step responses for tasks requiring precision and clarity.
• Ideal for educational explanations, system design reasoning, and code walkthroughs.

6. Large 200K context window

• Handles long documents, multi-file reasoning, or extended conversations with minimal loss of context.

7. Broad API support

• Works with Chat Completions, Responses, Realtime, Assistants, Batch, Embeddings, Image Generation, and more.
• Supports streaming and function calling for advanced workflows.

8. Positioned as a legacy reasoning model

• Remains extremely capable but formally succeeded by GPT-5, which offers stronger reasoning and performance.