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How Leaders in Tech Cut On-Device AI KV-Cache Memory by 37.5%

Apple introduced a compact, approximately 3-billion-parameter on-device model and a mixture-of-experts server model with a novel architecture tailored for Private Cloud Compute.

Apple’s on-device model shares KV caches between its two blocks, which reduces KV-cache memory usage by 37.5% and significantly improves time-to-first-token. Decoder weights are compressed to 2 bits per weight for the on-device model and 3.56 for the server model. After compression and adapter recovery, the on-device model shows about 4.6% regression on MGSM and 1.5% improvement on MMLU. The server model outperforms Qwen-2.5-VL in human evaluation of image responses at less than half the inference FLOPS.

37.5%
reduction in KV-cache memory usage for the on-device model, which also significantly improves time-to-first-token
87.5%
of synchronization overhead removed in Apple’s example with track block depth D = 4 (2L with tensor parallelism to L/D)
2-bpw
decoder weights of the on-device model via quantization-aware training (server model: 3.56-bpw via ASTC)
< half
the inference FLOPS of Qwen-2.5-VL for the server model, which outperforms it in human evaluation of image responses

The problem

Apple developed the on-device and server models to meet a wide range of performance and deployment requirements. The on-device model is optimized for efficiency and tailored for Apple silicon, enabling low-latency inference with minimal resource usage, while the server model is designed to deliver high accuracy and scalability for more complex tasks.

What they did

The on-device model is divided into two blocks with a 5:3 depth ratio, and the KV caches of block 2 are shared directly with those generated by the final layer of block 1.

The result

After compression and adapter recovery, Apple observes some slight quality regressions and even minor improvements: about 4.6% regression on MGSM and 1.5% improvement on MMLU for the on-device model, and 2.7% MGSM and 2.3% MMLU regression for the server model.

Limits

The server model is behind larger models such as Qwen-3-235B and the proprietary GPT-4o.

Figures come from the source below. Anything from another place is attributed in the text.

Source: Apple Machine Learning Research: 2025 foundation model updates ↗
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