In this section, you will find the steps to install the library, troubleshoot known issues, review changes between versions, and more.


skrl requires Python 3.6 or higher and the following libraries (they will be installed automatically):

Machine learning (ML) framework#

According to the specific ML frameworks, the following libraries are required:



Library Installation#

Python Package Index (PyPI)#

To install skrl with pip, execute:

pip install skrl["torch"]

GitHub repository#

Clone or download the library from its GitHub repository (

git clone
cd skrl
  • Install in editable/development mode (links the package to its original location allowing any modifications to be reflected directly in its Python environment)

    pip install -e .["torch"]
  • Install in the current Python site-packages directory (modifications to the code downloaded from GitHub will not be reflected in your Python environment)

    pip install .["torch"]

Discussions and issues#

To ask questions or discuss about the library visit skrl’s GitHub discussions

Bug detection and/or correction, feature requests and everything else are more than welcome. Come on, open a new issue!

Known issues and troubleshooting#

  1. When using the parallel trainer with PyTorch 1.12.

    See PyTorch issue #80831

    AttributeError: 'Adam' object has no attribute '_warned_capturable_if_run_uncaptured'
  2. When installing the JAX version in Python 3.7 (e.g. OmniIsaacGymEnvs or Isaac Orbit on Isaac Sim 2022.2.1 and earlier).

    ERROR: Ignored the following versions that require a different python version: 0.4.0 Requires-Python >=3.8; ...
    ERROR: Could not find a version that satisfies the requirement jax>=0.4.3; extra == "jax" (from skrl[jax]) (from versions: 0.0, ..., 0.3.25)
    ERROR: No matching distribution found for jax>=0.4.3; extra == "jax"

    JAX support for Python 3.7 is up to version 0.3.25, while skrl requires jax>=0.4.3. Furthermore, jaxlib<=0.3.25 builds are only available up to NVIDIA CUDA 11 and cuDNN 8.2 versions.

    However, it is possible to use skrl under these circumstances, subject to the following points:

    • Install JAX, Flax and Optax manually using pip install jax flax optax and ignore the installation errors for skrl.

    • The jax.Device = jax.xla.Device statement is required by skrl to support jax<0.4.3.

    • Overload models __hash__ method to avoid "TypeError: Failed to hash Flax Module".

  3. When training/evaluating using JAX in Python 3.7 (e.g. OmniIsaacGymEnvs or Isaac Orbit on Isaac Sim 2022.2.1 and earlier).

    TypeError: Failed to hash Flax Module. The module probably contains unhashable attributes

    Overload the __hash__ method for each defined model to avoid this issue:

    def __hash__(self):
        return id(self)
  4. When training/evaluating using JAX with the NVIDIA Isaac Gym Preview, Isaac Orbit or Omniverse Isaac Gym environments.

    PxgCudaDeviceMemoryAllocator fail to allocate memory XXXXXX bytes!! Result = 2
    RuntimeError: CUDA error: an illegal memory access was encountered

    NVIDIA environments use PyTorch as a backend, and both PyTorch (for CUDA kernels, among others) and JAX preallocate GPU memory, which can lead to out-of-memory (OOM) problems. Reduce or disable GPU memory preallocation as indicated in JAX GPU memory allocation to avoid this issue. For example:

    export XLA_PYTHON_CLIENT_MEM_FRACTION=.50  # lowering preallocated GPU memory to 50%


# Changelog

The format is based on [Keep a Changelog](

## [1.0.0] - 2023-08-16

Transition from pre-release versions (`1.0.0-rc.1` and`1.0.0-rc.2`) to a stable version.

This release also announces the publication of the **skrl** paper in the Journal of Machine Learning Research (JMLR):

Summary of the most relevant features:
- JAX support
- New documentation theme and structure
- Multi-agent Reinforcement Learning (MARL)

## [1.0.0-rc.2] - 2023-08-11
### Added
- Get truncation from `time_outs` info in Isaac Gym, Isaac Orbit and Omniverse Isaac Gym environments
- Time-limit (truncation) boostrapping in on-policy actor-critic agents
- Model instantiators `initial_log_std` parameter to set the log standard deviation's initial value

### Changed (breaking changes)
- Structure environment loaders and wrappers file hierarchy coherently
  Import statements now follow the next convention:
  - Wrappers (e.g.):
    - `from skrl.envs.wrappers.torch import wrap_env`
    - `from skrl.envs.wrappers.jax import wrap_env`
  - Loaders (e.g.):
    - `from skrl.envs.loaders.torch import load_omniverse_isaacgym_env`
    - `from skrl.envs.loaders.jax import load_omniverse_isaacgym_env`

### Changed
- Drop support for versions prior to PyTorch 1.9 (1.8.0 and 1.8.1)

## [1.0.0-rc.1] - 2023-07-25
### Added
- JAX support (with Flax and Optax)
- RPO agent
- IPPO and MAPPO multi-agent
- Multi-agent base class
- Bi-DexHands environment loader
- Wrapper for PettingZoo and Bi-DexHands environments
- Parameters `num_envs`, `headless` and `cli_args` for configuring Isaac Gym, Isaac Orbit
and Omniverse Isaac Gym environments when they are loaded

### Changed
- Migrate to `pyproject.toml` Python package development
- Define ML framework dependencies as optional dependencies in the library installer
- Move agent implementations with recurrent models to a separate file
- Allow closing the environment at the end of execution instead of after training/evaluation
- Documentation theme from *sphinx_rtd_theme* to *furo*
- Update documentation structure and examples

### Fixed
- Compatibility for Isaac Sim or OmniIsaacGymEnvs (2022.2.0 or earlier)
- Disable PyTorch gradient computation during the environment stepping
- Get categorical models' entropy
- Typo in `KLAdaptiveLR` learning rate scheduler
  (keep the old name for compatibility with the examples of previous versions.
  The old name will be removed in future releases)

## [0.10.2] - 2023-03-23
### Changed
- Update loader and utils for OmniIsaacGymEnvs 2022.2.1.0
- Update Omniverse Isaac Gym real-world examples

## [0.10.1] - 2023-01-26
### Fixed
- Tensorboard writer instantiation when `write_interval` is zero

## [0.10.0] - 2023-01-22
### Added
- Isaac Orbit environment loader
- Wrap an Isaac Orbit environment
- Gaussian-Deterministic shared model instantiator

## [0.9.1] - 2023-01-17
### Added
- Utility for downloading models from Hugging Face Hub

### Fixed
- Initialization of agent components if they have not been defined
- Manual trainer `train`/`eval` method default arguments

## [0.9.0] - 2023-01-13
### Added
- Support for Farama Gymnasium interface
- Wrapper for robosuite environments
- Weights & Biases integration
- Set the running mode (training or evaluation) of the agents
- Allow clipping the gradient norm for DDPG, TD3 and SAC agents
- Initialize model biases
- Add RNN (RNN, LSTM, GRU and any other variant) support for A2C, DDPG, PPO, SAC, TD3 and TRPO agents
- Allow disabling training/evaluation progressbar
- Farama Shimmy and robosuite examples
- KUKA LBR iiwa real-world example

### Changed (breaking changes)
- Forward model inputs as a Python dictionary
- Returns a Python dictionary with extra output values in model calls

### Changed
- Adopt the implementation of `terminated` and `truncated` over `done` for all environments

### Fixed
- Omniverse Isaac Gym simulation speed for the Franka Emika real-world example
- Call agents' method `record_transition` instead of parent method
to allow storing samples in memories during evaluation
- Move TRPO policy optimization out of the value optimization loop
- Access to the categorical model distribution
- Call reset only once for Gym/Gymnasium vectorized environments

### Removed
- Deprecated method `start` in trainers

## [0.8.0] - 2022-10-03
### Added
- AMP agent for physics-based character animation
- Manual trainer
- Gaussian model mixin
- Support for creating shared models
- Parameter `role` to model methods
- Wrapper compatibility with the new OpenAI Gym environment API
- Internal library colored logger
- Migrate checkpoints/models from other RL libraries to skrl models/agents
- Configuration parameter `store_separately` to agent configuration dict
- Save/load agent modules (models, optimizers, preprocessors)
- Set random seed and configure deterministic behavior for reproducibility
- Benchmark results for Isaac Gym and Omniverse Isaac Gym on the GitHub discussion page
- Franka Emika real-world example

### Changed (breaking changes)
- Models implementation as Python mixin

### Changed
- Multivariate Gaussian model (`GaussianModel` until 0.7.0) to `MultivariateGaussianMixin`
- Trainer's `cfg` parameter position and default values
- Show training/evaluation display progress using `tqdm`
- Update Isaac Gym and Omniverse Isaac Gym examples

### Fixed
- Missing recursive arguments during model weights initialization
- Tensor dimension when computing preprocessor parallel variance
- Models' clip tensors dtype to `float32`

### Removed
- Parameter `inference` from model methods
- Configuration parameter `checkpoint_policy_only` from agent configuration dict

## [0.7.0] - 2022-07-11
### Added
- A2C agent
- Isaac Gym (preview 4) environment loader
- Wrap an Isaac Gym (preview 4) environment
- Support for OpenAI Gym vectorized environments
- Running standard scaler for input preprocessing
- Installation from PyPI (`pip install skrl`)

## [0.6.0] - 2022-06-09
### Added
- Omniverse Isaac Gym environment loader
- Wrap an Omniverse Isaac Gym environment
- Save best models during training

## [0.5.0] - 2022-05-18
### Added
- TRPO agent
- DeepMind environment wrapper
- KL Adaptive learning rate scheduler
- Handle `gym.spaces.Dict` observation spaces (OpenAI Gym and DeepMind environments)
- Forward environment info to agent `record_transition` method
- Expose and document the random seeding mechanism
- Define rewards shaping function in agents' config
- Define learning rate scheduler in agents' config
- Improve agent's algorithm description in documentation (PPO and TRPO at the moment)

### Changed
- Compute the Generalized Advantage Estimation (GAE) in agent `_update` method
- Move noises definition to `resources` folder
- Update the Isaac Gym examples

### Removed
- `compute_functions` for computing the GAE from memory base class

## [0.4.1] - 2022-03-22
### Added
- Examples of all Isaac Gym environments (preview 3)
- Tensorboard file iterator for data post-processing

### Fixed
- Init and evaluate agents in ParallelTrainer

## [0.4.0] - 2022-03-09
### Added
- CEM, SARSA and Q-learning agents
- Tabular model
- Parallel training using multiprocessing
- Isaac Gym utilities

### Changed
- Initialize agents in a separate method
- Change the name of the `networks` argument to `models`

### Fixed
- Reset environments after post-processing

## [0.3.0] - 2022-02-07
### Added
- DQN and DDQN agents
- Export memory to files
- Postprocessing utility to iterate over memory files
- Model instantiator utility to allow fast development
- More examples and contents in the documentation

### Fixed
- Clip actions using the whole space's limits

## [0.2.0] - 2022-01-18
### Added
- First official release