Together AI Open-Sources OSCAR: An Attention-Aware 2-Bit KV Cache Quantization System for Long-Context LLM Serving

MarkTechPost / 5/26/2026

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Key Points

  • Together AI has open-sourced OSCAR, an INT2 (2-bit) KV cache quantization approach aimed at improving long-context LLM serving efficiency.
  • OSCAR uses attention-aware, offline-estimated covariance structures to compute separate rotations for keys and values, differing from earlier rotation methods that relied on data-oblivious Hadamard transforms.
  • At about 2.28 bits per KV element, OSCAR narrows the BF16 accuracy gap to 3.78 points on Qwen3-4B-Thinking-2507 and 1.42 points on Qwen3-8B.
  • The method targets substantial efficiency gains, including roughly an 8× reduction in KV memory usage and up to 3× faster decoding at 100K context length.
  • The release positions OSCAR as a practical system-level optimization for scaling long-context inference without proportionally increasing memory and latency.

Together AI has released OSCAR (Offline Spectral Covariance-Aware Rotation), an INT2 KV cache quantization method for long-context LLM serving. Unlike prior rotation-based approaches that apply data-oblivious Hadamard transforms, OSCAR derives separate rotations for keys and values from attention-aware covariance structures estimated offline. At 2.28 bits per KV element, OSCAR reduces the BF16 accuracy gap to 3.78 points on Qwen3-4B-Thinking-2507 and 1.42 points on Qwen3-8B, while delivering approximately 8× KV memory reduction and up to 3× decode speedup at 100K context length.

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