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Second-Order and Orthogonalized Optimizers

Second-order and orthogonalized optimizers exploit curvature information or the matrix structure of gradients rather than purely elementwise first-order statistics. This group spans quasi-Newton and Hessian-diagonal methods (L-BFGS, AdaHessian, Sophia), full-matrix and Kronecker-factored preconditioning (PSGD, Shampoo, SOAP), and orthogonalized-update methods in the Muon family. Venues reflect peer-reviewed acceptance where applicable; otherwise the arXiv year is listed.

Optimizer Venue Paper Code zij
Gauss-Newton Method Biometrika 1974 Quasi-likelihood functions, generalized linear models, and the Gauss-Newton method — —
Newton's Method ANL Technical Report 1982 Newton's method (ANL-82-8) — —
L-BFGS Mathematical Programming 1989 On the limited memory BFGS method for large scale optimization official LBFGS
Natural Gradient Neural Computation 1998 Natural Gradient Works Efficiently in Learning — —
K-FAC ICML 2015 Optimizing Neural Networks with Kronecker-factored Approximate Curvature — —
PSGD IEEE TNNLS 2018 Preconditioned Stochastic Gradient Descent official —
Shampoo ICML 2018 Shampoo: Preconditioned Stochastic Tensor Optimization official Shampoo
AdaHessian AAAI 2021 ADAHESSIAN: An Adaptive Second Order Optimizer for Machine Learning official Adahessian
Apollo arXiv 2020 Apollo: An Adaptive Parameter-wise Diagonal Quasi-Newton Method for Nonconvex Stochastic Optimization official —
K-BFGS / K-BFGS(L) NeurIPS 2020 Practical Quasi-Newton Methods for Training Deep Neural Networks — —
SGN arXiv 2020 On the Promise of the Stochastic Generalized Gauss-Newton Method for Training DNNs — —
SpiderSQN IEEE TNNLS 2022 Faster Stochastic Quasi-Newton Methods — —
TKFAC AAAI 2021 A Trace-restricted Kronecker-Factored Approximation to Natural Gradient — —
SGDHess NeurIPS 2022 Better SGD using Second-order Momentum — —
SketchySGD SIMODS 2024 SketchySGD: Reliable Stochastic Optimization via Randomized Curvature Estimates official —
Distributed Shampoo arXiv 2023 A Distributed Data-Parallel PyTorch Implementation of the Distributed Shampoo Optimizer for Training Neural Networks At-Scale official —
mL-BFGS TMLR 2023 mL-BFGS: A Momentum-based L-BFGS for Distributed Large-Scale Neural Network Optimization — —
Sophia ICLR 2024 Sophia: A Scalable Stochastic Second-order Optimizer for Language Model Pre-training official SophiaG
AdaFisher ICLR 2025 AdaFisher: Adaptive Second Order Optimization via Fisher Information official —
CRNAS arXiv 2024 Novel Optimization Techniques for Parameter Estimation — —
HesScale ICML 2024 Revisiting Scalable Hessian Diagonal Approximations for Applications in Reinforcement Learning official —
Muon Blog post 2024 Muon: An optimizer for hidden layers in neural networks official Muon
NysAct IEEE BigData 2024 NysAct: A Scalable Preconditioned Gradient Descent using Nystrom Approximation — —
OptiQ arXiv 2024 Second-Order Optimization via Quiescence — —
Q-Newton arXiv 2024 Q-Newton: Hybrid Quantum-Classical Scheduling for Accelerating Neural Network Training with Newton's Gradient Descent official —
SOAA arXiv 2024 Efficient Second-Order Neural Network Optimization via Adaptive Trust Region Methods — —
SOAP ICLR 2025 SOAP: Improving and Stabilizing Shampoo using Adam for Language Modeling official SOAP
AdaDiag arXiv 2025 Improving Adaptive Moment Optimization via Preconditioner Diagonalization — —
ADAGB2 arXiv 2025 Fast Stochastic Second-Order Adagrad for Nonconvex Bound-Constrained Optimization — —
AdaGO arXiv 2025 AdaGrad Meets Muon: Adaptive Stepsizes for Orthogonal Updates — —
AdaMuon arXiv 2025 AdaMuon: Adaptive Muon Optimizer official AdaMuon
ASGO NeurIPS 2025 ASGO: Adaptive Structured Gradient Optimization official —
AuON arXiv 2025 AuON: A Linear-time Alternative to Orthogonal Momentum Updates official —
COSMOS arXiv 2025 COSMOS: A Hybrid Adaptive Optimizer for Memory-Efficient Training of LLMs official —
FUSE IEEE CAI 2025 FUSE: First-Order and Second-Order Unified SynthEsis in Stochastic Optimization — —
Hessian-aware Scaling arXiv 2025 First-ish Order Methods: Hessian-aware Scalings of Gradient Descent — —
MAC IEEE ICDM 2025 MAC: An Efficient Gradient Preconditioning using Mean Activation Approximated Curvature — —
MuonClip arXiv 2025 Kimi K2: Open Agentic Intelligence community —
NorMuon ICML 2026 NorMuon: Making Muon more efficient and scalable official NorMuon
OCAR ICML 2025 Online Curvature-Aware Replay: Leveraging 2nd Order Information for Online Continual Learning — —
PolarGrad arXiv 2025 PolarGrad: A Class of Matrix-Gradient Optimizers from a Unifying Preconditioning Perspective official PolarGrad
ROOT arXiv 2025 ROOT: Robust Orthogonalized Optimizer for Neural Network Training official —
S-BFGS arXiv 2025 Efficient Stochastic BFGS methods Inspired by Bayesian Principles — —
SASSHA ICML 2025 SASSHA: Sharpness-aware Adaptive Second-order Optimization with Stable Hessian Approximation official —
Scion ICML 2025 Training Deep Learning Models with Norm-Constrained LMOs official Scion
SPlus arXiv 2025 A Stable Whitening Optimizer for Efficient Neural Network Training official SPlus
Muon^2 arXiv 2026 Muon^2: Boosting Muon via Adaptive Second-Moment Preconditioning — —
Nora arXiv 2026 Nora: Normalized Orthogonal Row Alignment for Scalable Matrix Optimizer — —
Pion arXiv 2026 Rethinking Muon Beyond Pretraining: Spectral Failures and High-Pass Remedies for VLA and RLVR — —
Spectral Sphere Optimizer (SSO) arXiv 2026 Controlled LLM Training on Spectral Sphere official —
LoRA-Muon arXiv 2026 LoRA-Muon: Spectral Steepest Descent on the Low-Rank Manifold — —
FOAM arXiv 2026 FOAM: Frequency and Operator Error-Based Adaptive Damping Method for Reducing Staleness-Oriented Error for Shampoo — —
Mousse arXiv 2026 Mousse: Rectifying the Geometry of Muon with Curvature-Aware Preconditioning official —
FISMO arXiv 2026 FISMO: Fisher-Structured Momentum-Orthogonalized Optimizer — —
DyKAF arXiv 2025 DyKAF: Dynamical Kronecker Approximation of the Fisher Information Matrix for Gradient Preconditioning — —
Double Preconditioning (DoPr) arXiv 2026 Double Preconditioning (DoPr): Optimization for Test-Time Performance, not Validation Loss — —
AdaCubic TMLR 2026 AdaCubic: An Adaptive Cubic Regularization Optimizer for Deep Learning official —
IFNSO arXiv 2026 IFNSO: Iteration-Free Newton-Schulz Orthogonalization official —
CAO arXiv preprint 2025 CAO: Curvature-Adaptive Optimization via Periodic Low-Rank Hessian Sketching — —
Turbo-Muon arXiv 2025 Turbo-Muon: Accelerating Orthogonality-Based Optimization with Pre-Conditioning official —
SR1 Cubic Quasi-Newton arXiv 2025 Symmetric Rank-One Quasi-Newton Methods for Deep Learning Using Cubic Regularization — —
KL-Shampoo ICLR 2026 Understanding and Improving Shampoo and SOAP via Kullback-Leibler Minimization official —
LLQR arXiv 2026 Layerwise LQR for Geometry-Aware Optimization of Deep Networks official —
Freon / Kaon arXiv 2026 Muon is Not That Special: Random or Inverted Spectra Work Just as Well — —
Mano arXiv 2026 Mano: Restriking Manifold Optimization for LLM Training official —
Atlas OPT 2025: 17th Annual Workshop on Optimization for Machine Learning (co-located with NeurIPS 2025) Atlas – Rethinking Optimizer Design for Stability and Speed — —