Apertus 1.5 Release Notes

Our latest release, Apertus 1.5, extends the 8B and 70B Apertus 1.0 models with image/audio understanding, an optional thinking mode, a four times longer context window, improved instruction-following, and better tool use. The updated 8B and 70B model weights were released to Hugging Face on July 24, 2026 under an Apache 2.0 license. Further details are now available from the project Technical Report, and summarized here.

Apertus 1.5 is a continued pretraining of the first generation model: adding 4 trillion tokens of text and multimodal training data to the 8B model and 2 trillion tokens to the 70B model, for a total of 19T and 17T, respectively. As with every Apertus release, the models are fully open: open weights, open data, open values, and full training details.

Key Enhancements

• Native Multimodal Understanding: Apertus 1.5 accepts images and audio alongside text, bringing documents, diagrams, and photos into the conversation. The models can also process spoken language, though this remains experimental.
• Thinking Mode: The models can be switched into a thinking mode to reason about the input before answering, which improves performance on reasoning problems.
• Long Context: The context window grows to 262,144 tokens, a 4x increase over Apertus 1.0.
• Improved Instruction-Following: Better instruction adherence than Apertus 1.0 gives more predictable and accurate responses.
• Improved Tool Use: The models are trained for better tool integration, allowing more effective use of external tools and APIs.
• Open Values: Stronger adherence to the Apertus Charter, which brings transparency to the model’s values and principles.

Training Process

The full Apertus 1.5 training pipeline

Multimodality Through the Tokenizer

Pre-Training

Starting from Apertus 1.0, we continue pretraining in four stages:

Post-Training

Post-training runs in five stages: SFT → long-context SFT → RL → DPO → charter alignment (SDPO).