PufferLib

Choose the version before choosing an API. Reviewed 2026-10-01:

For 5.0, read references/native-5.md. The reviewed revision is 6ffa5b10dbbbe4d1e8288367c7d9d3acd3bad4a2. Its CLI is ./puffer train after building an environment, not puffer train ENV_NAME. There is no 5.0 Python emulation/vector API or --slowly fallback.

The bundled plan schema deliberately supports only 3.0 and pinned 4.0; it does not launch training. All native/PufferLib training examples are source-reviewed, illustrative, and not executed in this review. Bundled synthetic checks are executed CPU tests, not evidence of PufferLib installation or learning quality. The PyPI sdist was hash-verified and its Python sources inspected; the moving 3.0 branch differs, including its load_policy and logger contracts.

Safe defaults

1. Start with bundled synthetic, CPU-only, network-free tools.
2. Do not import an arbitrary environment by dotted path. Bundled tools accept only allowlisted built-ins and slug identifiers.
3. Do not install or execute an unreviewed environment package, native extension, ROM, map, checkpoint, or pickle file.
4. Verify official source, immutable revision, licenses, checksums or attestations, and build hooks. Sandbox native builds and first execution.
5. Cap steps, environments, agents, workers, threads, buffers, memory, disk, render size, and wall time.
6. Keep training and evaluation environments/seeds separate.
7. Default logging to local/none. External logging requires explicit opt-in, disclosure acknowledgment, and separate artifact-upload approval.
8. Never pass W&B or Neptune credentials via CLI, INI, JSON, tags, run names, or logger configuration. Never print them.
9. Never dump all environment variables or recursively search for .env.
10. Hash checkpoint bytes before trusted, sandboxed loading; metadata inspection is not proof of safety.

First local checks

All bundled CLIs are dependency-free and emit strict JSON:

python3 scripts/env_template.py --help
python3 scripts/env_contract_validator.py
python3 scripts/benchmark_vectorization.py --backend serial
python3 scripts/train_template.py
python3 scripts/validate_plan.py
python3 scripts/repro_plan.py

Defaults are synthetic, deterministic, bounded, local, CPU-only, no-network, and dry-run where training would otherwise occur.

Installation and provenance

Published 3.0.0

PyPI supplies only pufferlib-3.0.0.tar.gz:

sha256: 7df3a3e3f5f894d78d2a1f5374097890aec01473183e748abefe4f3faa10eaa9
Requires-Python: >=3.9

After source/build review, create a pinned uv project:

uv venv --python 3.11
uv add --exact --no-sync "pufferlib==3.0.0"
uv lock
uv sync --frozen

These installation commands are illustrative and were not executed. Commit pyproject.toml and uv.lock; verify the archive digest and every resolved dependency. The source build can compile native code and fetch build assets, so resolve/build in a sandbox without credentials or sensitive mounts. The archive declares NumPy <2, Gymnasium <=0.29.1, and PettingZoo <=1.24.1; latest Gymnasium/NumPy are not valid substitutes for this profile. Its setup supports Linux/macOS and rejects other systems. Python classifiers alone do not establish a successful native build. The uploaded metadata does not pin Torch or CUDA; do not claim a supported CUDA matrix that PyPI does not declare.

Pinned 4.0 source

The reviewed branch head on 2026-07-23 was:

25647630e1b15330bb3153a5a0d3ff8d234c3acf

Pin the commit, not branch 4.0:

uv add --no-sync \
  "pufferlib @ git+https://github.com/PufferAI/PufferLib.git@25647630e1b15330bb3153a5a0d3ff8d234c3acf"
uv lock

The reviewed 4.0 package declares Python >=3.10 and Torch >=2.9. The reviewed PufferTank snapshot uses Ubuntu 24.04, Python 3.12, and an NVIDIA CUDA 13.0.2/cuDNN development image with the cu130 Torch index, but does not pin the exact Torch wheel or all system packages. Treat it as a reference, not a complete lock. Never execute a remote installer directly from a pipe.

Read references/training.md before any installation or build.

Environment workflow

1. Validate the contract

Gymnasium reset returns (observation, info). Step returns:

(observation, reward, terminated, truncated, info)

Validate spaces, shapes, dtypes, finite rewards, booleans, reset-before-step, reset-after-end, seeding, and cleanup. terminated is an MDP terminal; truncated is an external cutoff such as a time limit. Preserve the distinction for bootstrapping and metrics. Both flags can be true in general Gymnasium. Check autoreset timing and retain the final pre-reset observation; do not bootstrap from the next episode. The 3.0 trainer has unresolved truncation and inactive-agent mask handling, described in references/training.md.

python3 scripts/env_contract_validator.py \
  --steps 64 --episodes 8 --seed 42

2. Adapt only after review

Published 3.0 uses explicit wrappers:

import pufferlib.emulation

wrapped = pufferlib.emulation.GymnasiumPufferEnv(reviewed_gymnasium_instance)

For a reviewed PettingZoo Parallel environment:

wrapped = pufferlib.emulation.PettingZooPufferEnv(reviewed_parallel_instance)

There is no supported 3.0 pufferlib.emulate(...) shortcut matching the old skill. Read references/environments.md and references/integration.md.

3. Native environments

Published 3.0 PufferEnv requires single_observation_space, single_action_space, and num_agents before super().__init__(buf). It uses in-place vector buffers and returns separate terminal/truncation arrays plus a list of info dictionaries.

The reviewed 4.0 source uses C bindings. Start from upstream ocean/squared (single-agent) or ocean/target (multi-agent), build one environment in local/sanitized mode, and verify every buffer size/type/index before optimization.

Vectorization workflow

Published 3.0:

import pufferlib.vector

vecenv = pufferlib.vector.make(
    reviewed_creator,
    backend=pufferlib.vector.Serial,
    num_envs=4,
    seed=42,
)

Move to Multiprocessing only after serial traces pass. Record num_envs, num_workers, batch_size, zero-copy mode, start method, agent count, masks, and actual returned shapes. For multi-agent environments, batch length is based on agent slots, not necessarily num_envs.

The reviewed 4.0 config instead uses:

[vec]
total_agents = 4096
num_buffers = 2
num_threads = 16

Read references/vectorization.md. Benchmark fixed work with warmup and at least three repeats; report simulation and end-to-end training SPS separately. The bundled benchmark measures only its synthetic harness.

Policy workflow

Published 3.0 policies are Torch modules sized from single_observation_space/single_action_space. Stable recurrent composition uses encode_observations and decode_actions; structured emulation uses pufferlib.pytorch.nativize_dtype and nativize_tensor.

The reviewed 4.0 Torch fallback composes:

pufferlib.models.Policy(encoder=encoder, decoder=decoder, network=network)

It provides MLP, MinGRU, LSTM, and GRU network choices; --slowly selects this fallback instead of the native backend. Check output/state shapes, masks, finite values, gradients, and eager-versus-compiled behavior. See references/policies.md.

Training and evaluation

Published 3.0 trainer import:

from pufferlib import pufferl

# train_config must include the environment name for checkpoint naming.
trainer = pufferl.PuffeRL(train_config, vecenv, policy)

Reviewed 4.0 CLI:

puffer train ENV_NAME
puffer eval ENV_NAME --load-model-path EXACT_TRUSTED_PATH
puffer sweep ENV_NAME

Generate a plan instead of launching by default:

python3 scripts/train_template.py \
  --profile pypi-3.0.0 \
  --environment synthetic \
  --device cpu \
  --total-timesteps 10000

train_template.py emits a report envelope, not a bare plan. Its plan member is the input to validate_plan.py; passing the whole report is invalid. For the synthetic environment, command_preview is an empty list because there is no upstream training command to launch. To save and revalidate:

python3 scripts/train_template.py > training-report.json
python3 -c 'import json; r=json.load(open("training-report.json")); print(json.dumps(r["plan"], allow_nan=False, indent=2))' > plan.json
python3 scripts/validate_plan.py --root . --config plan.json

The handoff consists of the training report, extracted plan and validation report. A command preview exists only for a reviewed non-synthetic environment and remains partial until its environment-specific settings are resolved.

Validate a custom strict-JSON plan using the same bare-plan format:

python3 scripts/validate_plan.py --root . --config plan.json

The schema rejects secret-bearing keys, unbounded resources, dotted environment paths, invalid vector divisibility, mixed-version options, and coupled train/eval seeds. See references/training.md.

Logging

PufferLib 3.0 contains historical W&B and Neptune integrations; pinned 4.0 contains W&B. Neptune shut down on 2026-03-05 and the bundled planner rejects it. Native 5.0 uses local logs/Constellation and has no reviewed W&B or Neptune CLI flag. W&B remains an optional external service. It may transmit configuration, metrics, source metadata, hardware telemetry, output, and approved artifacts, with privacy, retention, access-control, and cost implications.

• W&B credential: named environment variable WANDB_API_KEY.
• Historical Neptune token name: NEPTUNE_API_TOKEN; do not configure new runs.
• Never put values in arguments/config/logs.
• Sanitize config keys before logging.
• Keep source/model upload off unless explicitly approved.

The reviewed 3.0 sdist and pinned 4.0 W&B training paths upload a model on completion. The 3.0 sdist has no --no-model-upload flag. The planner therefore requires explicit artifact opt-in as well as logging opt-in:

python3 scripts/train_template.py \
  --logger wandb \
  --enable-external-logging \
  --acknowledge-external-disclosure \
  --upload-checkpoints

It reports only the required variable name and never reads its value.

Checkpoint workflow

PufferLib 3.0 and the 4.0 Torch fallback use Torch serialization; the reviewed native 4.0 source writes opaque .bin weights. PyTorch warns that untrusted models are programs and that torch.load uses unpickling.

python3 scripts/inspect_checkpoint.py checkpoint.pt \
  --root . \
  --expected-sha256 0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef

The inspector hashes and classifies only. It does not call torch.load, import pickle/Torch, inspect archive members, or extract files. Verify source, license, architecture, environment revision, sidecar metadata, and checksum before any sandboxed load. Never use latest in a reproducible evaluation.

Bundled files

Scripts

• scripts/env_template.py — deterministic synthetic Gymnasium-style template.
• scripts/env_contract_validator.py — bounded contract and seed checks.
• scripts/benchmark_vectorization.py — capped serial/spawn synthetic benchmark.
• scripts/train_template.py — non-executing 3.0/4.0 training-plan generator.
• scripts/validate_plan.py — strict config/resource/security validator.
• scripts/inspect_checkpoint.py — metadata/hash inspection without deserialization.
• scripts/repro_plan.py — separate-seed evaluation and benchmark plan.

References

• references/native-5.md — current native build, environment, trainer and evaluation contracts.
• references/environments.md — Gymnasium, stable PufferEnv, emulation, native C.
• references/vectorization.md — backends, shapes, start methods, benchmarks.
• references/policies.md — version-specific policy contracts and state safety.
• references/training.md — installs, config, CLI, PuffeRL, eval, logs, checkpoints.
• references/integration.md — migration matrix, third-party and credential safety.

Dated upstream sources

• Neptune shutdown notice — service discontinued 2026-03-05; checked 2026-10-01.
• Current 5.0 source/CLI evidence is linked in references/native-5.md.

• PyPI pufferlib 3.0.0 — released 2025-06-23; checked 2026-07-23.
• PyPI 3.0.0 metadata — digest/dependencies and archive contents; rechecked 2026-10-01.
• PufferLib official docs — checked 2026-10-01; implementation details pinned in references/native-5.md.
• PufferLib source — source history and implementation; checked 2026-07-23.
• PufferTank 4.0 Dockerfile — CUDA/Python reference; checked 2026-07-23.
• PufferLib 2.0 paper — Reinforcement Learning Journal, 2025; use only for its stated benchmarks.
• PufferLib compatibility paper — submitted 2024-06-11; describes an earlier API/performance profile.