This is a research-grade PyTorch implementation of Danijar Hafner's Dreamer v4 model-based reinforcement learning algorithm. The core artifact is the `dreamer4` package, dominated by a monolithic `dreamer4/dreamer4.py` (~3000 lines) that implements `VideoTokenizer`/`SpaceTimeTokenizer`, `DynamicsWorldModel`, `AudioTokenizer`, and `StateTokenizer`. These classes build causal space-time transformers with separate space/time attention blocks, latent flow-matching diffusion with shortcut consistency, BYOL-style tokenizer pre-training, PoPE attention, and a large zoo of experimental loss terms (latent autoregressive loss, decorrelation, orthogonality, SigReg, self-flow distillation, shortcut loss). `dreamer4/trainers.py` provides training loops (VideoTokenizerTrainer, BehaviorCloneTrainer, DreamTrainer, SimTrainer) and `dreamer4/cli.py` exposes CLI entry points for training and serving the world model. The repository is hybrid: primarily research code, but packaged and tested like a library. It ships a pyproject.toml with pinned dependencies, a parametrized test suite (tests/test_dreamer.py, test_e2e.py, test_env_wrapper.py), a browser-based Snake environment with a Flask-style server (`dreamer4/web_env/`) used for human demonstration collection and replay-buffer inspection, and environment wrappers in `dreamer4/env.py` that record agent experience to folders or memmap replay buffers. Root-level scripts are the actual experiment entry points, targeting standard benchmarks: HalfCheetah (imagination RL), CartPole (dynamics + RL), MovingMNIST (tokenizer + dynamics), and Snake (PPO with dynamics model). Craftsmanship is above typical research code: clean package layout, pytest coverage across many hyperparameter combinations, self-contained utilities (LossNormalizer, tensor pack/unpack helpers, with_seed decorator, memmap replay-buffer helpers), and HuggingFace Accelerate integration for distributed/mixed-precision training. However, the single-file core, 100+ hyperparameter flags on trainers, scattered hard-coded constants, sparse docstrings, and reliance on volatile niche packages (x-transformers, h-net-dynamic-chunking, PoPE_pytorch, adam-atan2-pytorch) make long-term stability and code reuse risky. The repository is recently committed and appears maintained, but it is explicitly beta-status experimental research code, not a production system.