Claude Opus 4.5 vs Llama-3.1 Nemotron Ultra 253B

Claude Opus 4.5

Anthropic

Claude Opus 4.5, released by Anthropic in November 2025, is a large language model from the Claude 4.5 family built for demanding reasoning tasks, advanced code generation, and complex agentic workflows. It features a 200K token context window, 64K maximum output tokens, native image understanding, and extended thinking with configurable effort levels. Opus 4.5 targets deep analytical work, multi-step tool orchestration, and applications requiring sustained reasoning across long, complex tasks.

Llama-3.1 Nemotron Ultra 253B

NVIDIA

Llama-3.1-Nemotron-Ultra-253B-v1 is a 253-billion-parameter model from NVIDIA, derived from Meta's Llama 3.1 405B using neural architecture search (NAS) compression combined with NVIDIA's Nemotron post-training pipeline, which recovers and exceeds the base model's capability after structural compression. Released in April 2025, it supports toggling between a standard instruction mode and an extended reasoning mode via system prompt, allowing the same model to handle both rapid responses and deliberate chain-of-thought tasks. It is the flagship of the Nemotron family, available open-weight on HuggingFace and through NVIDIA NIM for enterprise inference.