Apertus 1.5 Release Notes

Apertus 1.5 is an Apache 2.0–licensed update to the open 8B and 70B Apertus models that adds native image and experimental audio understanding, an optional reasoning-focused thinking mode, a 262,144-token context window, and improved instruction following and tool use. Built through continued pretraining with 4 trillion additional tokens for the 8B model and 2 trillion for the 70B model, it uses early fusion to represent text, images, and audio as tokens within the same architecture, while producing text outputs only. Post-training combines supervised fine-tuning, long-context tuning, reinforcement learning with verifiable rewards, preference optimization, and, for the 8B model, charter alignment intended to reflect the project’s stated values. The release reports gains in coding, multilingual tasks, reasoning with thinking mode, multimodal understanding, Swiss legal tasks, and machine translation, while noting that it remains behind leading frontier open-weight models in some areas. Project Apertus emphasizes reproducibility by publishing model weights, intermediate checkpoints, training data information, code, evaluation results, and structured evaluation records, and notes that Apertus 1.5 is available through Hugging Face, selected applications, and several API providers.

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