GPT-OSS 20B vs Claude 5 Sonnet

• 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. Anthropic's most agentic Sonnet yet

• A substantial upgrade over Sonnet 4.6 on reasoning, tool use, coding, and knowledge work - narrows the gap to Opus 4.8 while staying at Sonnet pricing.
• Early partners describe it finishing multi-step jobs end to end where prior Sonnet models used to stall halfway.

2. Clear benchmark gains over Sonnet 4.6

• 63.2% on SWE-bench Pro (vs 58.1%), 80.4% on Terminal-Bench 2.1 (vs 67.0%), 81.2% on OSWorld-Verified (vs 78.5%), and 57.4% on Humanity's Last Exam with tools (vs 46.8%).
• On the GDPval-AA v2 knowledge-work benchmark it edges past Opus 4.8 (1,618 vs 1,615).

3. Near-Opus performance at a fraction of the price

• Priced at $3/M input and $15/M output - 40% cheaper than Opus 4.8's $5/$25 - with introductory pricing of $2/$10 through Aug 31, 2026 during the rollout.
• Supports low, medium, high, and xhigh effort levels, covering a wider cost-performance range than Sonnet 4.6 and matching Opus 4.8 on some tasks at higher effort.

4. Long-context, long-horizon reliability

• Full 1M token context window with up to 128K output tokens.
• Adaptive thinking automatically decides how long to reason; better self-correction, fewer tool errors, and steadier follow-through across long agent sessions in Claude Code and Cowork.

5. Safer and more honest than its predecessor

• Lower rates of hallucination, sycophancy, and misaligned behavior than Sonnet 4.6 on Anthropic's automated safety audits.
• Deliberately limited cyber capability compared with Opus-class models, shipped with cyber safeguards enabled by default.

6. Updated tokenizer

• Uses a new tokenizer (shared with the Opus 4.7/4.8 line) that can map the same text to up to 1.35x more tokens than Sonnet 4.6 - introductory pricing is set so the switch is roughly cost-neutral.