Llama 3.1 70B Instruct, Llama 3.1 8B Instruct, and Llama 3.3 70B Instruct are all Meta open-weights models released under the Llama 3 community license with 131K context windows. The 3.1 generation launched July 2024; Llama 3.3 70B followed in December 2024, targeting the same 70B hardware footprint with improved alignment. This comparison spans two parameter sizes and two generations. The 8B is the smallest here and the cost floor. It handles straightforward instruction-following, classification, summarization, and light coding tasks, but does not match either 70B model on complex reasoning, multi-turn coherence, or structured output reliability. MMLU sits in the low-to-mid 70s. For volume-heavy pipelines where the quality difference to 70B is not user-visible, it is worth benchmarking the gap before paying 70B rates. Llama 3.1 70B represents the first point in Meta's roadmap where 131K context arrived at a commercially accessible parameter count. MMLU around 79-80. It is a solid model for its generation but has been largely superseded within the Meta ecosystem by the 3.3 update. Teams running it in production are typically pinned to a specific checkpoint for reproducibility rather than by preference. Llama 3.3 70B is the current default recommendation at this parameter class from Meta. The December 2024 release delivers meaningfully better instruction-following accuracy and agentic task performance at the same 70B footprint and roughly equivalent inference cost. If you are selecting between 3.1 70B and 3.3 70B for a new deployment, there is no strong case for the older version. Pick the 8B for high-throughput, cost-sensitive pipelines. Pick Llama 3.3 70B as the default 70B-class choice. Only pick 3.1 70B if a specific weight hash is required for reproducibility.