verl → Relax Recipe Migration

This skill guides migration of RL training recipes (reward functions, tool environments, multi-turn rollouts, training scripts) from the verl framework to Relax.

For detailed import/code mapping tables and transformation templates, see references/migration_mapping.md.

Migration overview

A verl recipe typically consists of:

Reward 两层机制说明：Relax 的 reward 系统分为两层。

1. 内置 reward（relax/engine/rewards/）：通过 --rm-type deepscaler|math|dapo|... 直接使用，无需写 Python 代码。如果 verl 的 compute_score 恰好等价于某个内置类型（如简单数学答案校验），可直接使用 --rm-type 而不必迁移代码。
2. 自定义 reward（--custom-rm-path）：当 --custom-rm-path 被设置时，RewardExecutor 会优先加载用户函数，跳过内置分发。verl 的 compute_score 通常包含算法特定的打分逻辑，属于自定义范畴，因此迁移目标是 examples/<algo>/reward_<algo>.py，通过 --custom-rm-path examples.<algo>.reward_<algo>.reward_func 注册。

The algorithm code lives under examples/<algo>/ in Relax — not inside the framework core.

Core architecture differences

1. Configuration paradigm

2. Data protocol

3. Reward system

4. Rollout / multi-turn

Workflow

Step 0: Create the target directory

mkdir -p examples/<algo>
touch examples/<algo>/__init__.py

Step 1: Migrate reward function

This is the most critical step. verl and Relax have different reward function interfaces.

verl pattern (function-based, synchronous, routed by data_source)

# verl: standalone function, dispatched by data_source string
def compute_score(data_source, solution_str, ground_truth, extra_info=None):
    """
    Called by NaiveRewardManager for each sample.
    Args:
        data_source: str - dataset identifier (e.g. "openai/gsm8k")
        solution_str: str - model's decoded response text
        ground_truth: str - ground truth answer
        extra_info: dict - additional metadata
    Returns:
        float or dict with "score" key
    """
    if data_source == "openai/gsm8k":
        return gsm8k.compute_score(solution_str, ground_truth)
    elif data_source in ["math_dapo", "math"]:
        return math_dapo.compute_score(solution_str, ground_truth)
    ...

Registered via Hydra config:

custom_reward_function:
  path: /path/to/my_reward.py
  name: compute_score
  reward_kwargs:
    key1: value1

Relax pattern (function-based, async, per-sample)

# Relax: async function, operates on Sample dataclass
from relax.utils.types import Sample

def compute_score(predict_str: str, ground_truth: str, extra_info: dict | None = None) -> dict:
    """Synchronous single-sample scoring. Must return dict with 'score' key."""
    ...
    return {"score": final_score, "acc": ..., ...}

async def reward_func(args, sample: Sample, **kwargs):
    """Entry point called by Relax engine. Wraps compute_score."""
    ground_truth = sample.label
    return compute_score(sample.response, ground_truth, extra_info=sample.metadata)

Registered via CLI:

--custom-rm-path examples.<algo>.reward_<algo>.reward_func

Key conversion rules:

1. Remove data_source dispatch — verl routes rewards by data_source string; in Relax, each example has its own reward module, so the dispatch is unnecessary. Extract the specific scoring logic for your dataset.
2. Wrap in async reward_func — Add async def reward_func(args, sample: Sample, **kwargs) as entry point. For batch/group reward, use async def reward_func(args, samples: list[Sample], **kwargs) and add --group-rm to CLI.
3. Map data fields — solution_str → sample.response, ground_truth → sample.label (preprocess verl parquet to extract ground_truth into a flat label column; see Step 4), extra_info → sample.metadata.
4. Return dict with "score" — Both frameworks support returning a dict; ensure the "score" key is present (batch mode returns list[dict]). When returning dict, add --reward-key score to CLI so Relax can extract the float value via sample.reward[args.reward_key]. Alternatively, return a plain float (no --reward-key needed).
5. Remove verl imports — Replace from verl.utils.reward_score import ... with direct imports of the scoring logic, or copy the relevant scoring functions.
6. Handle reward_kwargs — In verl, extra kwargs are passed via custom_reward_function.reward_kwargs; in Relax, create a YAML file and pass via --custom-config-path path/to/config.yaml. All keys are set as args attributes via setattr(args, k, v), accessible as args.key1 in your reward function.

Step 2: Migrate tool environment (if multi-turn/agentic)

Only needed for multi-turn or tool-calling recipes. Skip for pure single-turn reward-only recipes.

verl pattern (BaseTool)

from verl.tools.base_tool import BaseTool
from verl.tools.schemas import OpenAIFunctionToolSchema, ToolResponse

class MyTool(BaseTool):
    def __init__(self, config: dict, tool_schema: OpenAIFunctionToolSchema):
        super().__init__(config, tool_schema)

    async def create(self, instance_id=None, **kwargs) -> tuple[str, ToolResponse]:
        """Create a tool instance for a trajectory."""
        return str(uuid4()), ToolResponse()

    async def execute(self, instance_id: str, parameters: dict, **kwargs) -> tuple[ToolResponse, float, dict]:
        """Execute tool and return (response, step_reward, metrics)."""
        result = do_something(parameters)
        return ToolResponse(text=result), 0.0, {}

    async def calc_reward(self, instance_id: str, **kwargs) -> float:
        """Calculate final reward based on tool state."""
        return 0.0

    async def release(self, instance_id: str, **kwargs):
        """Release tool instance."""
        pass

Registered via YAML:

tools:
  - class_name: "verl.tools.my_tool.MyTool"
    config:
      type: native
    tool_schema:
      type: "function"
      function:
        name: "my_tool"
        description: "Tool description"
        parameters: {...}

Relax pattern (BaseInteractionEnv)

from examples.<algo>.base_env import BaseInteractionEnv
from relax.utils.types import Sample

class MyAgentEnv(BaseInteractionEnv):
    def __init__(self, *, max_turns, image=None):
        self.max_turns = max_turns
        self.image = image
        self.turn = 0

    def reset(self):
        """Return (observation, info). No arguments — sample data passed via build_env()."""
        self.turn = 0
        return {"obs_str": "Initial prompt", "role": "user"}, {}

    def step(self, response_text: str):
        """Parse tool calls from response, execute, return (obs_dict, done, info)."""
        self.turn += 1
        tool_result = self._execute_tool(response_text)
        done = self.turn >= self.max_turns
        obs = {
            "obs_str": f"<tool_response>{tool_result}</tool_response>",
            "role": "user",
        }
        return obs, done, {"tool_result": tool_result}

    def close(self):
        pass

def build_env(sample: Sample = None, args=None, **_) -> MyAgentEnv:
    """Factory function, required by Relax rollout."""
    max_turns = args.max_turns if args else 5
    image = None
    if sample and sample.multimodal_inputs:
        images = sample.multimodal_inputs.get("images") or sample.multimodal_inputs.get("image")
        if images:
            image = images[0]
    return MyAgentEnv(max_turns=max_turns, image=image)

Key conversion rules:

1. BaseTool → BaseInteractionEnv — verl tools are stateless async services with create/execute/calc_reward/release; Relax envs are stateful objects with reset()/step()/close().
2. Tool schema — verl uses OpenAI function tool schema in YAML; Relax handles tool parsing in the env's step() method.
3. Step reward — verl returns (ToolResponse, step_reward, metrics) from execute; in Relax, step reward is handled separately (in the reward function or env info dict).
4. Instance management — verl uses instance_id for lifecycle management; Relax instantiates one env per sample via build_env().
5. Observation format — verl returns ToolResponse(text=...) objects; Relax returns dicts {"obs_str": text, "role": "user", "multi_modal_data": {...}}.
6. Copy base_env.py — from examples/deepeyes/base_env.py or import BaseInteractionEnv from there.
7. Create config YAML — with max_turns and rollout_interaction_env_path.

Step 3: Migrate rollout (if multi-turn/agentic)

For multi-turn/agentic recipes, the multi-turn rollout logic lives in a generate() function.

verl approach: Multi-turn is handled internally by the rollout worker with multi_turn.enable=True in config. Tools are registered via YAML and executed automatically.

Relax approach: Multi-turn is handled by a custom generate() function specified via --custom-generate-function-path.

Recommendation: Copy examples/deepeyes/rollout.py into your example directory and update DEFAULT_ENV_MODULE to point to your env module:

DEFAULT_ENV_MODULE = "examples.<algo>.env_<algo>"

Then configure in the launch script:

--custom-generate-function-path examples.<algo>.rollout.generate

And in the config YAML (loaded via --custom-config-path):

max_turns: 5
rollout_interaction_env_path: examples.<algo>.env_<algo>

This ensures each example is self-contained — no cross-example dependencies.

Only modify the rollout further if your algorithm has custom turn logic (e.g., parallel tool execution, custom stopping conditions, special token budget management).

Step 4: Migrate dataset handling

verl pattern

verl uses Parquet files with specific columns, loaded by a dataset class:

# Data columns in parquet:
# - "prompt": chat messages (list of dicts or string)
# - "reward_model.ground_truth": ground truth for reward computation
# - "data_source": dataset identifier for reward routing
# - "extra_info": additional metadata dict
# - "images": (optional) image data for multimodal

# Hydra config:
data:
  train_files: /path/to/train.parquet
  val_files: /path/to/test.parquet
  train_batch_size: 1024
  max_prompt_length: 512
  max_response_length: 1024

Relax pattern

Relax also uses Parquet files but specifies column mapping via CLI:

ROLLOUT_ARGS=(
    --prompt-data "['/path/to/train.parquet']"
    --input-key prompt              # column containing chat messages
    --label-key label               # column containing ground truth (plain string)
    --metadata-key extra_info       # column containing metadata
    --multimodal-keys '{"image":"images"}'  # multimodal column mapping
    --apply-chat-template           # apply chat template to prompts
)

Data preprocessing for verl parquet:

verl parquet files are not directly compatible with Relax. You must write a conversion script (typically scripts/tools/process_<algo>.py) and mention it in the run script header so users know to run it first. Key transformations:

1. reward_model → label: verl stores ground truth in a reward_model dict column (e.g., {"style": "rule", "ground_truth": "72"}), but Relax expects sample.label to be a plain string. Extract it into a flat label column.
2. Image data: If the dataset is multimodal, preserve the image column (e.g., extract raw bytes from preprocessed_images). Then set --multimodal-keys '{"image":"<column_name>"}' in the launch script.
3. extra_info: Preserve the extra_info column if it exists; map via --metadata-key extra_info.

# scripts/tools/process_<algo>.py — conversion script template
import pandas as pd

def convert_row(row):
    result = {
        "prompt": row["prompt"],  # keep chat format as-is
        "label": row["reward_model"]["ground_truth"],
    }
    # Preserve images for multimodal datasets
    if "preprocessed_images" in row:
        result["image"] = [img["bytes"] for img in row["preprocessed_images"]]
    # Preserve metadata
    if "extra_info" in row:
        result["extra_info"] = row["extra_info"]
    return result

df = pd.read_parquet("verl_data/train.parquet")
df_out = pd.DataFrame([convert_row(row) for _, row in df.iterrows()])
df_out.to_parquet("relax_data/train.parquet", index=False)

Then add a data conversion reminder in the run script header:

# Prerequisites:
#   1. Convert data:  python3 scripts/tools/process_<algo>.py \
#                       --input-dir /path/to/verl/data.parquet \
#                       --output-dir /path/to/relax/data.parquet
#   2. Set env vars:  MODEL_DIR=/path/to/models  DATA_DIR=/path/to/data
#   3. Run:           bash examples/<algo>/run_<algo>.sh

Key conversion rules:

1. data.train_files → --prompt-data "[...]" (wrap in JSON list)
2. data.val_files → --eval-prompt-data <name> <files...>
3. data.train_batch_size → --global-batch-size
4. data.max_prompt_length → --rollout-max-prompt-len
5. data.max_response_length → --rollout-max-response-len
6. Column mapping: use --input-key, --label-key, --metadata-key, --multimodal-keys
7. Preprocess verl parquet — extract reward_model["ground_truth"] into a flat label column; --label-key reads the column value as-is into sample.label, so it should be a plain string, not a dict.
8. If verl uses a custom dataset class (data.custom_cls), extract the data preprocessing logic and apply it offline to the Parquet files before loading in Relax.

Step 5: Migrate training launch script

verl pattern

python3 -m verl.trainer.main_ppo \
    algorithm.adv_estimator=grpo \
    data.train_files=$HOME/data/gsm8k/train.parquet \
    data.val_files=$HOME/data/gsm8k/test.parquet \
    data.train_batch_size=1024 \
    data.max_prompt_length=512 \
    data.max_response_length=1024 \
    actor_rollout_ref.model.path=Qwen/Qwen3-8B \
    actor_rollout_ref.actor.optim.lr=1e-6 \
    actor_rollout_ref.actor.use_kl_loss=True \
    actor_rollout_ref.actor.kl_loss_coef=0.001 \
    actor_rollout_ref.actor.kl_loss_type=low_var_kl \
    actor_rollout_ref.rollout.name=sglang \
    actor_rollout_ref.rollout.gpu_memory_utilization=0.6 \
    actor_rollout_ref.rollout.n=5 \
    actor_rollout_ref.rollout.tensor_model_parallel_size=2 \
    trainer.n_gpus_per_node=8 \
    trainer.nnodes=1 \
    trainer.save_freq=20 \
    trainer.test_freq=5 \
    trainer.total_epochs=15

Relax pattern

Relax run scripts rely on a two-layer environment setup:

The generated script should always support both Colocate (sync) and Fully Async modes via a MODE parameter, defaulting to sync (colocate). This way the user can switch between modes without rewriting the script:

#!/bin/bash
# Usage: bash examples/<algo>/run_<algo>.sh [sync|async]

set -ex
set -o pipefail

MODE=${1:-${MODE:-"sync"}}    # Arg $1 > env $MODE > default "sync"

TIMESTAMP=$(date "+%Y-%m-%d-%H:%M:%S")

SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" &>/dev/null && pwd)"
# Auto-source local environment when not launched via an external entrypoint.
# local.sh sets MODEL_CONFIG_DIR, RUNTIME_ENV_JSON, PYTHONPATH, and starts Ray.
if [ -z "${RELAX_ENTRYPOINT_MODE:-}" ]; then
    source "${SCRIPT_DIR}/../../scripts/entrypoint/local.sh"
fi
source "${MODEL_CONFIG_DIR}/<model>.sh"

PROJECT_NAME="${PROJECT_NAME:=Relax/dev/<algo>}"
EXP_NAME="<model>-<algo>-fully-${MODE}-${TIMESTAMP}"

CKPT_ARGS=(
    --hf-checkpoint ${MODEL_DIR}/<Model>
    --ref-load ${MODEL_DIR}/<Model>
    # --load ${MODEL_DIR}/<Model>_mcore/     # for resuming
    # --save ${MODEL_DIR}/<Model>_mcore/
    # --save-interval 4
    --megatron-to-hf-mode bridge
)

ROLLOUT_ARGS=(
    --prompt-data "${PROMPT_SET}"
    --input-key prompt
    --label-key label
    --metadata-key extra_info
    --multimodal-keys '{"image":"image"}'   # if multimodal; omit for text-only
    --reward-key score
    --apply-chat-template
    --custom-rm-path examples.<algo>.reward_<algo>.reward_func
    --num-rollout ${NUM_ROLLOUT}
    --rollout-batch-size 32
    --n-samples-per-prompt 8
    --rollout-max-response-len 1024
    --rollout-max-prompt-len 512
    --rollout-temperature 1
    # global-batch-size MUST equal rollout-batch-size × n-samples-per-prompt
    --global-batch-size 256
    --rollout-shuffle
    --use-fault-tolerance
)

PERF_ARGS=(
    --tensor-model-parallel-size 4     # TP × PP must divide actor GPU count
    --sequence-parallel
    --pipeline-model-parallel-size 1
    --context-parallel-size 1
    --expert-model-parallel-size 1
    --expert-tensor-parallel-size 1
    --recompute-granularity full
    --recompute-method uniform
    --recompute-num-layers 1
    --micro-batch-size 1
    --max-tokens-per-gpu 9216          # dynamic batch memory cap
)

GRPO_ARGS=(
    --advantage-estimator grpo
    --use-kl-loss
    --kl-loss-coef 0.001
    --kl-loss-type low_var_kl
    --entropy-coef 0
    --eps-clip 0.2
    --eps-clip-high 0.28
    --use-tis
)

OPTIMIZER_ARGS=(
    --optimizer adam
    --lr 1e-6
    --lr-decay-style constant
    --weight-decay 0.1
    --adam-beta1 0.9
    --adam-beta2 0.98
    --clip-grad 1.0
    --optimizer-cpu-offload
    --overlap-cpu-optimizer-d2h-h2d
    --use-precision-aware-optimizer
)

SGLANG_ARGS=(
    --rollout-num-gpus-per-engine 2
    --sglang-mem-fraction-static 0.8
)

LOG_ARGS=(
    --use-tensorboard
    --use-metrics-service
    --tb-project-name ${PROJECT_NAME}
    --tb-experiment-name ${EXP_NAME}
)

MISC_ARGS=(
    --attention-dropout 0.0
    --hidden-dropout 0.0
    --accumulate-allreduce-grads-in-fp32
    --attention-softmax-in-fp32
    --attention-backend flash
)

EVAL_ARGS=(
    --eval-interval 100
    --eval-prompt-data <name> ${TEST_FILES}
)

#=============================================================================
# Launch: fully async or colocate (sync)
#=============================================================================
mkdir -p logs

if [ "${MODE}" = "async" ]; then
    # Fully Async: actor/rollout/reference/actor_fwd/advantages on separate GPUs.
    # 8 GPU example: actor=4, rollout=2, reference=1, actor_fwd=1, advantages=CPU
    python3 relax/entrypoints/train.py \
        --resource '{"actor": [1, 4], "rollout": [1, 2], "reference": [1, 1], "actor_fwd": [1, 1], "advantages": [1, 0]}' \
        --max-staleness 3 \
        --num-data-storage-units 1 \
        --num-iters-per-train-update 8 \
        --ref-actor-config '{"tensor_model_parallel_size": 1, "max_tokens_per_gpu": 16384, "sequence_parallel": false, "only_load_weight": true}' \
        --fully-async \
        --use-health-check \
        "${MODEL_ARGS[@]}" "${CKPT_ARGS[@]}" "${ROLLOUT_ARGS[@]}" \
        "${OPTIMIZER_ARGS[@]}" "${GRPO_ARGS[@]}" "${LOG_ARGS[@]}" \
        "${PERF_ARGS[@]}" "${SGLANG_ARGS[@]}" "${MISC_ARGS[@]}" \
        2>&1 | tee logs/${EXP_NAME}.log
else
    # Colocate (sync): actor and rollout share the same GPUs.
    python3 relax/entrypoints/train.py \
        --resource '{"actor": [1, 8], "rollout": [1, 8]}' \
        --max-staleness 1 \
        --num-data-storage-units 1 \
        --colocate \
        --use-health-check \
        --balance-data \
        "${MODEL_ARGS[@]}" "${CKPT_ARGS[@]}" "${ROLLOUT_ARGS[@]}" \
        "${OPTIMIZER_ARGS[@]}" "${GRPO_ARGS[@]}" "${LOG_ARGS[@]}" \
        "${PERF_ARGS[@]}" "${SGLANG_ARGS[@]}" "${MISC_ARGS[@]}" \
        2>&1 | tee logs/${EXP_NAME}.log
fi

Colocate vs Fully Async: key differences

The script template above supports both modes. Here is what changes between them:

verl does not have a direct equivalent of fully async mode. verl uses a colocated architecture. No verl config maps to --fully-async.

GPU resource allocation for fully async

8 GPU example:
├── Actor (training):     4 GPU  (TP=4, PP=1, DP=1)
├── Rollout (inference):  2 GPU  (SGLang engines)
├── Reference (forward):  1 GPU  (TP=1 via ref-actor-config)
├── ActorFwd (forward):   1 GPU  (TP=1 via ref-actor-config)
└── Advantages (compute): 0 GPU  (CPU only)

16 GPU large model example:
├── Actor (training):     8 GPU  (TP=4, PP=2, DP=1)
├── Rollout (inference):  4 GPU  (SGLang engines)
├── Reference (forward):  2 GPU  (TP=2 via ref-actor-config)
├── ActorFwd (forward):   2 GPU  (TP=2 via ref-actor-config)
└── Advantages (compute): 0 GPU  (CPU only)

--ref-actor-config overrides parallelism for Reference and ActorFwd (typically single GPU, TP=1):

--ref-actor-config '{"tensor_model_parallel_size": 1, "max_tokens_per_gpu": 16384, "sequence_parallel": false, "only_load_weight": true}'

Key conversion rules

1. python3 -m verl.trainer.main_ppo → python3 relax/entrypoints/train.py (both sync and async; local.sh already starts Ray via ray start --head, so no ray job submit needed for single-node; do NOT add --runtime-env-json)
2. Hydra dot-notation key.subkey=value → argparse --key-subkey value
3. actor_rollout_ref.model.path → --hf-checkpoint + --ref-load
4. actor_rollout_ref.rollout.n → --n-samples-per-prompt
5. data.train_batch_size → --global-batch-size
6. trainer.n_gpus_per_node / trainer.nnodes → --resource (for sync: {"actor": [1, N], "rollout": [1, N]} where N = n_gpus_per_node × nnodes; for async: split across roles)
7. trainer.save_freq → --save-interval
8. trainer.test_freq → --eval-interval
9. trainer.total_epochs → --num-epoch N (preferred; maps directly to verl's epoch concept) or --num-rollout (rollout batch count)
10. algorithm.adv_estimator=grpo → --advantage-estimator grpo
11. Model config: use source "${MODEL_CONFIG_DIR}/<model>.sh" instead of inline TP/PP settings
12. Checkpoint: verl auto-handles model loading from HF path; Relax uses --hf-checkpoint for initial, --load for resume

Notes on specific parameters

On-policy constraint (critical):

--global-batch-size MUST equal --rollout-batch-size × --n-samples-per-prompt to ensure on-policy training. If this constraint is violated, training degrades to off-policy. For example: --rollout-batch-size 32 --n-samples-per-prompt 8 → --global-batch-size 256. In fully async mode, each batch is additionally trained for --num-iters-per-train-update iterations, improving data utilization.

Default optimizer options:

Always include these three optimizer flags unless there is a specific reason not to:

--optimizer-cpu-offload              # offload optimizer state to CPU memory
--overlap-cpu-optimizer-d2h-h2d      # overlap D2H/H2D transfers with computation
--use-precision-aware-optimizer      # mixed-precision optimizer for memory efficiency

Multimodal datasets:

If the verl dataset contains image data, you MUST:

1. Preserve image columns in the data conversion script (extract raw bytes from preprocessed_images or keep images as-is)
2. Add --multimodal-keys '{"<relax_key>":"<column_name>"}' to ROLLOUT_ARGS (e.g., --multimodal-keys '{"image":"image"}')

Fully async specific:

• --num-iters-per-train-update — training epochs per rollout batch; higher values (4-8) improve data efficiency. Especially important in async mode where rollout data generation is continuous.
• --max-staleness — controls how far Rollout can run ahead of Actor. Value of 3 means up to 2 unconsumed rollout batches in TransferQueue. Recommended 2-3 for production.
• --max-tokens-per-gpu — dynamic batching memory limit; recommended 9216 for 9B models.
• TP × PP must divide Actor GPU count — e.g., Actor 4 GPUs with PP=1 → TP can be 1/2/4; Actor 8 GPUs with TP=4, PP=2 → DP=1. Constraint: Actor_GPUs = TP × PP × DP.

Argument mapping quick reference

Fully Async specific parameters (no verl equivalent)

These parameters are Relax-only and have no verl counterpart. They are used in the async branch of the MODE switch in Step 5:

Recipe type decision tree

Is the verl recipe single-turn (no tools/multi-turn)?
├── YES → Migrate: Step 1 (reward) + Step 4 (data) + Step 5 (launch script)
│   └── Target structure:
│       examples/<algo>/
│       ├── __init__.py
│       ├── reward_<algo>.py
│       └── run_<algo>.sh           # MODE=${1:-"sync"}, supports both sync & async
│
└── NO (multi-turn / tool-calling)
    ├── Does it use verl BaseTool? → Step 2 (migrate tool → BaseInteractionEnv)
    ├── Does it use custom multi-turn logic? → Step 3 (migrate rollout)
    └── All recipes → Step 1 + Step 4 + Step 5
    └── Target structure:
        examples/<algo>/
        ├── __init__.py
        ├── base_env.py             # Copy from examples/deepeyes/base_env.py
        ├── env_<algo>.py           # BaseInteractionEnv subclass + build_env()
        ├── reward_<algo>.py        # compute_score + reward_func
        ├── rollout.py              # Copy from examples/deepeyes/rollout.py, update DEFAULT_ENV_MODULE
        ├── <algo>_config.yaml      # max_turns, rollout_interaction_env_path
        └── run_<algo>.sh           # MODE=${1:-"sync"}, supports both sync & async

Note: Step 5 always generates a dual-mode script (MODE=${1:-"sync"}).
The user switches to fully async by passing "async" — no separate migration step needed.

Important rules

• ALWAYS create a new examples/<algo>/ directory; never modify relax/engine/rewards/
• ALWAYS provide an async def reward_func(args, sample: Sample, **kwargs) entry point (single-sample mode, default) or async def reward_func(args, samples: list[Sample], **kwargs) (batch mode, with --group-rm)
• ALWAYS return a dict with a "score" key from the reward function (or list[dict] in batch mode); add --reward-key score to CLI when returning dict
• ALWAYS use Sample dataclass fields (sample.response, sample.label, sample.metadata)
• ALWAYS write a data conversion script (scripts/tools/process_<algo>.py) and reference it in the run script header; verl parquet is NOT directly compatible with Relax; When doing so, You need to tell the user that they need to perform data conversion in advance.
• ALWAYS preserve image columns in multimodal datasets; add --multimodal-keys to the launch script
• ALWAYS ensure --global-batch-size = --rollout-batch-size × --n-samples-per-prompt for on-policy training
• ALWAYS include --optimizer-cpu-offload --overlap-cpu-optimizer-d2h-h2d --use-precision-aware-optimizer in optimizer config
• NEVER use verl imports (from verl...) in Relax code
• NEVER use Hydra config syntax in Relax launch scripts
• NEVER modify Relax core code (relax/) for recipe migration — keep everything in examples/
• NEVER add --runtime-env-json — this is handled by the entrypoint layer
• ALWAYS copy scoring logic from verl's reward_score/ rather than importing it
• PREFER --custom-rm-path for reward registration over modifying RewardExecutor
• PREFER --custom-config-path YAML for passing extra reward config (replaces verl's reward_kwargs)
• ALWAYS generate dual-mode scripts with MODE=${1:-${MODE:-"sync"}} — supports positional arg, env var, and default; colocate (sync) by default
• ALWAYS use python3 relax/entrypoints/train.py directly for both modes — local.sh already starts Ray via ray start --head, no ray job submit needed for single-node
• ALWAYS ensure TP × PP divides Actor GPU count in fully async mode (constraint: Actor_GPUs = TP × PP × DP)
• ALWAYS add --ref-actor-config for Reference/ActorFwd in the async branch of the launch script

LLM-as-Judge reward migration

If the verl recipe uses an LLM-based reward (e.g., via OpenAI API), migrate as follows:

verl typically calls OpenAI API synchronously or via a custom reward function. Relax reward functions are async, making it natural to use httpx.AsyncClient or openai.AsyncOpenAI:

import httpx
from relax.utils.types import Sample

_client = httpx.AsyncClient(timeout=60)

async def reward_func(args, sample: Sample, **kwargs):
    """LLM-as-Judge reward using async HTTP."""
    judge_url = getattr(args, "judge_url", "http://localhost:8000/v1/chat/completions")
    judge_model = getattr(args, "judge_model", "judge-model")

    resp = await _client.post(judge_url, json={
        "model": judge_model,
        "messages": [
            {"role": "system", "content": "Rate the following answer..."},
            {"role": "user", "content": f"Question: {sample.prompt}\nAnswer: {sample.response}"},
        ],
        "max_tokens": 64,
        "temperature": 0,
    })
    result = resp.json()
    score_text = result["choices"][0]["message"]["content"]
    score = float(score_text.strip()) / 10.0  # normalize
    return {"score": score}

Pass judge_url and judge_model via --custom-config-path:

# examples/<algo>/<algo>_config.yaml
judge_url: "http://localhost:8000/v1/chat/completions"
judge_model: "Qwen/Qwen3-8B"

References

• references/migration_mapping.md - Detailed import mapping table, data field mapping, and code transformation patterns
• verl documentation: https://verl.readthedocs.io/en/latest/
• verl reward function guide: https://verl.readthedocs.io/en/latest/preparation/reward_function.html