Stable-Baselines3 vs 
Gymnasium
Stable-Baselines3 vs Gymnasium compared for 2026 — features, license, ease of use, performance and which one to choose. Reliable RL algorithms you can actually trust vs The standard interface for reinforcement learning.
Updated regularly · curated by OpenSourceAI.tech
Stable-Baselines3 vs Gymnasium at a glance
| Spec | Stable-Baselines3 | Gymnasium |
|---|---|---|
| Category | Robotics & embodied AI | Robotics & embodied AI |
| Type | RL algorithms | RL environment API |
| License | MIT | MIT |
| Runs locally | Yes | Yes |
| Primary language | Python | Python |
| Ease of use | Beginner | Beginner |
| Best for | getting a working policy without reimplementing PPO from a paper | learning RL, or benchmarking an algorithm against a known baseline |
| GitHub stars | 13.6k | 12.2k |
How Stable-Baselines3 and Gymnasium score
| Criterion | Stable-Baselines3 | Gymnasium |
|---|---|---|
| Popularity | 3.0 | 3.0 |
| Maintenance | 5.0 | 5.0 |
| Ease of use | 5.0 | 5.0 |
| Privacy | 5.0 | 5.0 |
| License freedom | 5.0 | 5.0 |
Scores are computed automatically from public signals — GitHub stars (popularity), recent commit activity (maintenance), license type (freedom), local-first design (privacy) and onboarding complexity (ease of use). Indicative, not a verdict.
What each one is
Stable-Baselines3
Stable-Baselines3 provides carefully tested PyTorch implementations of the main RL algorithms — PPO, SAC, TD3 — with sane defaults.
- Implementations verified against published results
- Excellent documentation
- Works out of the box with Gymnasium
Gymnasium
Gymnasium is the maintained successor to OpenAI Gym: one API that every RL algorithm and environment speaks.
- The interface the whole RL ecosystem implements
- Dozens of environments included
- Actively maintained, unlike the original Gym
Key differences
Stable-Baselines3 is rL algorithms, while Gymnasium is rL environment API. In short, Stable-Baselines3 fits getting a working policy without reimplementing PPO from a paper, and Gymnasium fits learning RL, or benchmarking an algorithm against a known baseline.
Which should you choose?
Choose Stable-Baselines3 for getting a working policy without reimplementing PPO from a paper. Choose Gymnasium for learning RL, or benchmarking an algorithm against a known baseline.
There is rarely one winner — many setups use both. The right pick depends on your hardware, your team's skills, and whether you value simplicity or control.
Frequently asked questions
Is Stable-Baselines3 or Gymnasium easier to use?
Both sit at a similar level (Beginner). Your choice should come down to fit rather than difficulty.
Are Stable-Baselines3 and Gymnasium free?
Stable-Baselines3 is free and open source (MIT), and Gymnasium is free and open source (MIT). Neither charges for the core software.
Can I run Stable-Baselines3 and Gymnasium locally?
Stable-Baselines3: yes · Gymnasium: yes. Both can be used without sending your data to a third-party cloud where their setup allows.
Stable-Baselines3 vs Gymnasium — which should I pick in 2026?
Choose Stable-Baselines3 for getting a working policy without reimplementing PPO from a paper. Choose Gymnasium for learning RL, or benchmarking an algorithm against a known baseline.
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