State Space Models

Oct 12, 2026

• AWS

  Can we change an AI model’s architecture without retraining it from scratch?

  The Transformer architecture’s memory cost scales with token count, making long-context AI agents expensive. In controlled comparisons of three state space models - Gated KalmaNet, Gated DeltaNet, and Mamba-2 - Gated KalmaNet performed best, offering variable-length inference without retraining. Priming identifies which attention layers can be replaced by state space models using a sliding-window attention proxy, then reuses pre-trained weights to convert them into hybrid architectures without retraining, reducing pretraining cost by over 99%. A 32-billion-parameter hybrid model matches the original Transformer’s reasoning quality while decoding up to twice as fast or reaching correct answers in two-thirds of wall-clock time. The team extended hybrid context to 256K tokens without additional training and released primed models at 8B and 32B scales along with training code, kernels, and a vLLM plugin under Apache 2.0.

• NVIDIA

  ReplaySSM: Rethinking State Storage for Faster Hybrid-Model Decoding

  Hybrid models interleave state-space model (SSM) layers with attention layers, but SSM layers can become a decoding bottleneck at serving batch sizes due to memory-bound state updates. ReplaySSM represents the SSM state as a checkpoint plus a buffer of recent inputs, separating output computation from state updates. This reduces state memory traffic by roughly half, simplifies rollback for speculative decoding by avoiding state snapshots, and supports low-precision state reads without propagating rounding error through the recurrence, enabling separate precision for output computation and state updates. Evaluated on Nemotron 3 and Qwen3.5 models from 4B to 120B parameters on H100 and B300 GPUs, ReplaySSM achieves 1.20× to 1.47× faster decode steps at batch size 256, with end-to-end gains growing with batch size. The technique is integrated into TensorRT-LLM, vLLM, SGLang, and FlashInfer, and runs in production in GLM-5.3-Flash and Kimi-K3.