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State Space Models (SSMs) like Mamba

Sequence models with a fixed-size recurrent state — S4 and HiPPO, Mamba and Mamba-2, hybrid SSM-attention models, related linear-recurrent architectures, applications beyond text, limits versus attention, tutorials and code.

64 topics•9 categories•Updated October 2026

Understanding State Space Models

5 entries

State space models (SSMs) are sequence models that carry a fixed-size hidden state forward through the sequence, updating it with a linear recurrence taken from classical control theory. Because the recurrence can also be computed as a convolution during training, SSMs train in parallel like Transformers yet run inference one step at a time with constant memory and cost per token, instead of a KV cache that grows with context length. Structured SSMs such as S4 showed strong results on long-range benchmarks; Mamba made the state transition input-dependent (selective), which lets the model decide what to remember or forget, and Mamba-2 connected SSMs to attention through structured state space duality. Pure SSMs can trail Transformers at tasks such as exact copying and in-context retrieval, so many recent models are hybrids that mix SSM and attention layers. Related linear-recurrent models include RWKV, RetNet, xLSTM and Griffin. This page collects papers, tutorials, models and libraries. The choice between SSM, attention and hybrid depends on context length, memory budget and the retrieval demands of the task.

Foundations: From HiPPO to S4

10 entries

The papers that built structured state space sequence models.

Mamba and Selective State Spaces

7 entries

The selective SSM and its successors.

Hybrid and Related Linear-Recurrent Models

10 entries

Models that mix SSMs with attention or use similar recurrences.

Vision, Genomics, Graphs & Other Domains

6 entries

SSMs beyond text.

Surveys, Limits & Theory

4 entries

Where SSMs fall short and how the field maps out.

Tutorials, Blogs & Explainers

6 entries

Readable introductions.

Code, Models & Libraries

8 entries

Implementations and checkpoints.

Related Pages

8 entries

Neighbouring pages on this site.

Frequently Asked Questions

Why does deep learning need statistics?

Training objectives such as cross-entropy and squared error are maximum likelihood estimates under assumed noise models, and questions about overfitting, evaluation, uncertainty and data shift are statistical questions. Without them it is hard to tell a real improvement from noise.

What statistics topics should I learn first for deep learning?

Start with random variables and distributions, expectation and variance, maximum likelihood and Bayes' theorem, then the bias-variance tradeoff, cross-validation and the bootstrap. After that, calibration, hypothesis testing for model comparison and distribution shift matter most in practice.

How do I know whether one model is really better than another?

Evaluate on held-out data, report uncertainty (for example confidence intervals from the bootstrap or variation across random seeds), and use an appropriate test when comparing models. The evaluation section lists papers on comparing classifiers and on error bars for language-model evaluations.

What is calibration and why does it matter?

A model is calibrated when its stated probabilities match observed frequencies. Guo et al. found that modern neural networks are often overconfident, and the uncertainty section lists methods such as temperature scaling, deep ensembles and conformal prediction.

Does the bias-variance tradeoff still apply to large neural networks?

The classical U-shaped curve describes many models, but work on double descent shows that test error can fall again as models grow past the point of fitting the training data. The generalisation section lists the main papers.

How is this page different from Probability Theory for AI?

That page covers probability, Bayesian inference and generative models. This page focuses on statistical practice for deep learning: estimation and regularisation, generalisation, evaluation and significance, uncertainty, distribution shift and experiment design.