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Every prime-rl entrypoint uses pydantic-config: TOML files for reproducible base configs, CLI flags for one-off overrides.
AI agents working in this repo: the equivalent runbook is at skills/configs/SKILL.md, with extra runtime hints (where config classes live, validator conventions, the trainer-side enable_token_export flag) that aren’t surfaced here.

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Table of Contents

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Sources and Precedence

Field values come from three sources — Pydantic defaults, TOML files (passed with @), and CLI flags. They’re layered in this order, with later sources winning:
  1. Defaults declared on the Pydantic model.
  2. TOML files passed with @, left to right — later files override earlier ones.
  3. CLI flags in dotted, kebab-case form (--model.name).

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TOML Composition

The @ token introduces a TOML file. Multiple @ arguments compose left-to-right, deep-merged — unset fields in an overlay keep the base value: 
uv run rl @ examples/reverse_text/rl.toml                      # one file
uv run rl @ base.toml @ overlay.toml                           # left to right
uv run rl --trainer @ trainer.toml --orchestrator @ orch.toml  # per-section
uv run rl @ base.toml --trainer @ trainer.toml                 # mixed
Mind the space: @ path/to/x.toml, not @path/to/x.toml.

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CLI Overrides

CLI flags mirror the TOML tree using dots: 
--max-steps 50                              # top-level
--model.name Qwen/Qwen3-4B                  # nested
--trainer.optim.lr 1e-5                     # double-nested
--inference.parallel.tp 4
Field names are snake_case in TOML (max_model_len) and kebab-case on the CLI (--max-model-len).
Renamed fields keep their old name as a validation alias — e.g. rollouts_per_example is still accepted in TOML and CLI after being renamed to group_size. Mixing the two names across sources is safe.

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Inspecting and Validating

uv run rl --help                                       # full schema
uv run rl @ rl.toml --dry-run --output-dir /tmp/check  # write resolved configs

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Syntax

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Booleans

CLI uses paired flags: bare --flag sets True, --no-flag sets False. TOML must be explicit: 
uv run rl @ rl.toml --clean-output-dir       # True
uv run rl @ rl.toml --no-clean-output-dir    # False

clean_output_dir = true

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Lists

CLI accepts space-separated values or a JSON literal. TOML uses an array literal. Both forms target the same field: 
uv run rl @ rl.toml --trainer.model.lora.target-modules q_proj k_proj v_proj
uv run rl @ rl.toml --trainer.model.lora.target-modules '["q_proj", "k_proj", "v_proj"]'

[trainer.model.lora]
target_modules = ["q_proj", "k_proj", "v_proj"]
Overlay TOMLs replace lists wholesale — an overlay that wants to add one item must still spell out the full list. For arrays of tables (e.g. environments), see Environments.

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Dicts

CLI takes a JSON literal. TOML uses a table or inline-table. CLI dicts deep-merge with TOML dicts — CLI keys win on conflict but don’t wipe the file’s keys: 
uv run rl @ rl.toml --orchestrator.train.env.0.args \
  '{"dataset_name": "openai/gsm8k", "dataset_subset": "main"}'

[[orchestrator.train.env]]
args = { dataset_name = "openai/gsm8k", dataset_subset = "main" }

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Optional Sub-Configs

Many sub-configs are typed SomeConfig | None. Two patterns enable them:
  • Bare flag with defaults: --model.compile or, in TOML, an empty section [model.compile]. The sub-config materializes with all-default values.
  • Enable and set fields together: --model.compile.fullgraph (CLI) or any populated [model.compile] table (TOML).
To disable a sub-config that’s on by default, use --no-<name> on the CLI or assign the string "None" in TOML (see None). This is how [ckpt], [model.lora], [model.compile], [trainer.wandb], etc. are turned on and off.

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None

TOML has no null. Use the string "None", which the loader coerces: 
[inference.model]
max_model_len = "None"
On the CLI: --inference.model.max-model-len None.

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Discriminated Unions

Loss, advantage, optimizer, scheduler, weight broadcast transport, and several others are discriminated unions. Set the type field to pick a variant: 
[trainer.optim]
type = "muon"
lr = 1e-5
mu = 0.95
Omit type to keep the default variant.

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Environments ([[orchestrator.train.env]])

Training environments are an array of tables — set one per env, optionally with sampling weights: 
[[orchestrator.train.env]]
id = "math-env"
name = "gsm8k"
args = { dataset_name = "openai/gsm8k", dataset_subset = "main" }
ratio = 3  # 75% of batches

[[orchestrator.train.env]]
id = "reverse-text"
ratio = 1  # default — 25% of batches

[[orchestrator.eval.env]]
id = "math-env"
name = "gsm8k-eval"
args = { dataset_name = "openai/gsm8k", dataset_subset = "main" }
ratio defaults to 1 (equal weight per env); values are relative weights normalized to probabilities across envs. args is forwarded verbatim to the environment’s load_environment(**args). The same id can appear multiple times across train and eval (or with different args) — useful for evaluating on a held-out split of the env you’re training on, or comparing two configurations of the same env side by side. When id is reused, set a distinct name on each entry; name defaults to id and must be unique across all envs in the same group.

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Environment Variables

OS environment variables exported into launched component process(es). In rl configs, top-level [env_vars] applies to trainer, inference, and orchestrator: 
[env_vars]
HF_HUB_OFFLINE = "1"
TOKENIZERS_PARALLELISM = "false"
Component-specific tables layer on top: 
[trainer.env_vars]
NCCL_DEBUG = "INFO"
PYTORCH_CUDA_ALLOC_CONF = "expandable_segments:False"

[inference.env_vars]
VLLM_USE_DEEP_GEMM = "1"

[orchestrator.env_vars]
PI_USAGE_BASE_URL = "https://..."
The rl launcher applies these the same way in both single-node and multi-node (SLURM) runs. Precedence, low to high:
  1. The launcher’s own defaults — your env_vars override these.
  2. Your top-level [env_vars].
  3. Your [component.env_vars].
  4. Orchestration-critical vars the launcher always sets last — CUDA_VISIBLE_DEVICES (GPU partitioning) and WANDB_SHARED_* (the single shared W&B run) — these cannot be overridden from env_vars.
For standalone sft and inference configs, [env_vars] applies to that entrypoint’s process(es). For disaggregated P/D inference, the role-specific deployment.{prefill,decode}_env_vars layer on top of any shared inference env vars.

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Examples

The shipped end-to-end examples in examples/ are the canonical, kept-up-to-date references — the rest of the repo’s TOMLs (under configs/) are CI- and debug-internal and may drift. Each example directory has its own README with the full launch story. Basic (1–8 GPUs):
  • Reverse Text — Qwen3-0.6B reversing a chunk of text. Tiny single-turn SFT + RL; runs on a single consumer GPU in minutes.
  • Wordle — Qwen3-1.7B playing Wordle. Multi-turn SFT + RL; 2–4 H100s.
  • Alphabet Sort — Qwen3-4B-Instruct-2507 sorting names alphabetically. Multi-turn LoRA RL without SFT warmup; one H100.
  • Wiki Search — Qwen3-4B-Instruct-2507 answering trivia by web-searching Wikipedia. Multi-turn with tool use.
  • Hendrycks Sanity — DeepSeek-R1-Distill-Qwen-1.5B on a filtered MATH subset. Useful for algorithm ablations.
Advanced (32–2048 GPUs, SLURM):

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Worked Example: Compose, Override, Dry-Run

Start from a shipped base config, override two fields on the CLI, and dry-run: 
uv run rl @ examples/reverse_text/rl.toml \
  --wandb.name my-experiment \
  --trainer.optim.lr 5e-6 \
  --output-dir /tmp/reverse-dry \
  --dry-run
Then inspect the resolved config: 
ls /tmp/reverse-dry/configs/
# rl.toml  trainer.toml  orchestrator.toml  inference.toml
Each per-process TOML reflects the final, validated configuration that the actual run would consume — exactly what each process sees when started standalone (uv run trainer @ /tmp/reverse-dry/configs/trainer.toml, etc.). This is the easiest way to bisect a misbehaving config: dry-run a known-good base, dry-run your overlay, diff the two.