diff --git a/skyrl-train/.env.llm_judge b/skyrl-train/.env.llm_judge
new file mode 100644
index 0000000000..3b07cf7a24
--- /dev/null
+++ b/skyrl-train/.env.llm_judge
@@ -0,0 +1,3 @@
+OPENAI_API_KEY="<openai_api_key>"
+# optionally, enter wandb if logging with wandb
+# WANDB_API_KEY=<wandb_api_key>
\ No newline at end of file
diff --git a/skyrl-train/examples/llm_as_a_judge/gsm8k_dataset_judge.py b/skyrl-train/examples/llm_as_a_judge/gsm8k_dataset_judge.py
new file mode 100644
index 0000000000..a50d72fdce
--- /dev/null
+++ b/skyrl-train/examples/llm_as_a_judge/gsm8k_dataset_judge.py
@@ -0,0 +1,90 @@
+# Copyright 2024 Bytedance Ltd. and/or its affiliates
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""
+Preprocess the GSM8k dataset to parquet format
+"""
+
+import argparse
+import re
+import os
+
+import datasets
+
+
+def extract_solution(solution_str):
+    solution = re.search("#### (\\-?[0-9\\.\\,]+)", solution_str)
+    assert solution is not None
+    final_solution = solution.group(0)
+    final_solution = final_solution.split("#### ")[1].replace(",", "")
+    return final_solution
+
+
+if __name__ == "__main__":
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--output_dir", default="~/data/gsm8k_llm_judge")
+
+    args = parser.parse_args()
+
+    args.output_dir = os.path.expanduser(args.output_dir)
+
+    data_source = "openai/gsm8k"
+
+    dataset = datasets.load_dataset(data_source, "main")
+
+    train_dataset = dataset["train"]
+    val_dataset = dataset["test"]
+
+    instruction_following = 'Let\'s think step by step and output the final answer after "####".'
+
+    # add a row to each data item that represents a unique id
+    def make_map_fn(split):
+        def process_fn(example, idx):
+            question_raw = example.pop("question")
+
+            question = question_raw + " " + instruction_following
+
+            answer_raw = example.pop("answer")
+            solution = extract_solution(answer_raw)
+            data = {
+                "data_source": data_source,
+                "prompt": [
+                    {
+                        "role": "user",
+                        "content": question,
+                    }
+                ],
+                # TODO: just repeating the full data preprocess script for a single env change isn't very convenient.
+                "env_class": "llm_as_a_judge",
+                "reward_spec": {
+                    "method": "rule",
+                    "ground_truth": solution,
+                },
+                "extra_info": {
+                    "split": split,
+                    "index": idx,
+                    "answer": answer_raw,
+                    "question": question_raw,
+                },
+            }
+            return data
+
+        return process_fn
+
+    train_dataset = train_dataset.map(function=make_map_fn("train"), with_indices=True)
+    val_dataset = val_dataset.map(function=make_map_fn("test"), with_indices=True)
+
+    output_dir = args.output_dir
+    os.makedirs(output_dir, exist_ok=True)
+    train_dataset.to_parquet(os.path.join(output_dir, "train.parquet"))
+    val_dataset.to_parquet(os.path.join(output_dir, "validation.parquet"))
diff --git a/skyrl-train/examples/llm_as_a_judge/llm_judge_env.py b/skyrl-train/examples/llm_as_a_judge/llm_judge_env.py
new file mode 100644
index 0000000000..a006f9c7a9
--- /dev/null
+++ b/skyrl-train/examples/llm_as_a_judge/llm_judge_env.py
@@ -0,0 +1,84 @@
+from skyrl_gym.envs.base_text_env import BaseTextEnv, BaseTextEnvStepOutput
+from typing import Any
+from typing import Dict
+from omegaconf import DictConfig
+from openai import OpenAI
+import os
+import re
+
+PROMPT = """
+You are a strict math evaluation assistant.
+
+Compare the following **gold** and **predicted** math solutions. Your job is to determine if the predicted solution is mathematically correct and if the predicted solution ends with a line of the form:
+
+#### <number>
+
+You must only give a score of "1" if:
+- The final line of the predicted solution **ends with `#### <number>`**, and
+- The number **matches the final answer in the gold solution** exactly.
+
+Instructions:
+- You may provide internal reasoning or explanation before giving your final judgment.
+- Your final judgment must appear as a separate line at the end of your response, in the format:
+
+### Final Score: 1
+
+or
+
+### Final Score: 0
+
+Do not include any explanation after the final score.
+"""
+
+
+class GSM8kLLMJudgeEnv(BaseTextEnv):
+    """
+    Example implementtion of GSM8k environment with LLM as judge.
+
+    Use LLM as judge to evaluate the answer similarity with the ground truth.
+    """
+
+    def __init__(self, env_config: DictConfig, extras: Dict[str, Any] = {}):
+        super().__init__()
+
+        assert "reward_spec" in extras, "reward_spec field is required"
+        assert "ground_truth" in extras["reward_spec"], "ground_truth is required in reward_spec field"
+        self.ground_truth = extras["reward_spec"]["ground_truth"]
+
+        # Set up OpenAI client
+        openai_api_key = os.getenv("OPENAI_API_KEY")
+        if openai_api_key is None:
+            raise ValueError("`OPENAI_API_KEY` must be set for Llm as a judge env")
+        self.llm_judge_client = OpenAI(base_url=env_config.base_url, api_key=openai_api_key)
+        self.model = env_config.model
+
+    def _get_reward(self, action: str) -> float:
+        message = PROMPT + f"\n\nGOLD SOLUTION:\n{self.ground_truth}\n\nPREDICTED SOLUTION:\n{action}\n\nAnswer:"
+
+        try:
+            response = self.llm_judge_client.chat.completions.create(
+                model=self.model, messages=[{"role": "user", "content": message}]
+            )
+            reply = response.choices[0].message.content.strip()
+
+            # Try to parse score from "### Final Score: x"
+            match = re.search(r"### Final Score:\s*([01](?:\.0)?)", reply)
+            if match:
+                return float(match.group(1))
+
+            # Fallback: raw "1" or "0"
+            if reply.strip() in {"1", "0"}:
+                return float(reply.strip())
+
+            print(f"Unrecognized reward output: {reply}")
+            return 0.0
+
+        except Exception as e:
+            print(f"LLM Judge error: {type(e).__name__}: {e}")
+            return 0.0
+
+    def step(self, action: str) -> BaseTextEnvStepOutput:
+        done = True
+        reward = self._get_reward(action)
+
+        return BaseTextEnvStepOutput(observations=[], reward=reward, done=done, metadata={})
diff --git a/skyrl-train/examples/llm_as_a_judge/main_llm_judge.py b/skyrl-train/examples/llm_as_a_judge/main_llm_judge.py
new file mode 100644
index 0000000000..c3e8050d95
--- /dev/null
+++ b/skyrl-train/examples/llm_as_a_judge/main_llm_judge.py
@@ -0,0 +1,36 @@
+"""
+uv run --isolated --extra vllm -m examples.llm_as_a_judge.main_llm_judge
+"""
+
+import ray
+import hydra
+from omegaconf import DictConfig
+from skyrl_train.utils import initialize_ray
+from skyrl_train.entrypoints.main_base import BasePPOExp, config_dir, validate_cfg
+from skyrl_gym.envs import register
+
+
+@ray.remote(num_cpus=1)
+def skyrl_entrypoint(cfg: DictConfig):
+    # Register the llm_as_a_judge environment inside the entrypoint task (no need to modify the skyrl-gym package).
+    register(
+        id="llm_as_a_judge",
+        entry_point="examples.llm_as_a_judge.llm_judge_env:GSM8kLLMJudgeEnv",
+    )
+
+    # make sure that the training loop is not run on the head node.
+    exp = BasePPOExp(cfg)
+    exp.run()
+
+
+@hydra.main(config_path=config_dir, config_name="ppo_base_config", version_base=None)
+def main(cfg: DictConfig) -> None:
+    # validate the arguments
+    validate_cfg(cfg)
+
+    initialize_ray(cfg)
+    ray.get(skyrl_entrypoint.remote(cfg))
+
+
+if __name__ == "__main__":
+    main()
diff --git a/skyrl-train/examples/llm_as_a_judge/run_llm_judge.sh b/skyrl-train/examples/llm_as_a_judge/run_llm_judge.sh
new file mode 100644
index 0000000000..d3a468cbc6
--- /dev/null
+++ b/skyrl-train/examples/llm_as_a_judge/run_llm_judge.sh
@@ -0,0 +1,57 @@
+set -x
+
+# Colocated GRPO training+generation for Qwen2.5-Coder-1.5B-Instruct on GSM8k dataset.
+# Uses 1 node with 4 GPUs.
+# uv run examples/llm_as_a_judge/gsm8k_dataset_judge.py --output_dir $HOME/data/gsm8k_llm_judge
+# add OPENAI_API_KEY and WANDB_API_KEY to .env.llm_judge
+# bash examples/llm_as_a_judge/run_llm_judge.sh
+
+DATA_DIR="$HOME/data/gsm8k_llm_judge"
+CKPT_PATH="$HOME/ckpts/llm_judge"
+
+NUM_GPUS=4
+NUM_INFERENCE_ENGINES=4
+TP_SIZE=1
+LOGGER=wandb
+
+# We use a smaller batch size here for demonstration
+uv run --isolated --extra vllm --env-file .env.llm_judge -m examples.llm_as_a_judge.main_llm_judge \
+  data.train_data="['$DATA_DIR/train.parquet']" \
+  data.val_data="['$DATA_DIR/validation.parquet']" \
+  trainer.algorithm.advantage_estimator="grpo" \
+  trainer.policy.model.path="Qwen/Qwen2.5-1.5B-Instruct" \
+  trainer.placement.colocate_all=true \
+  trainer.strategy=fsdp2 \
+  trainer.placement.policy_num_gpus_per_node=$NUM_GPUS \
+  trainer.placement.ref_num_gpus_per_node=$NUM_GPUS \
+  generator.num_inference_engines=$NUM_INFERENCE_ENGINES \
+  generator.inference_engine_tensor_parallel_size=$TP_SIZE \
+  trainer.epochs=20 \
+  trainer.eval_batch_size=32 \
+  trainer.eval_before_train=false \
+  trainer.eval_interval=5 \
+  trainer.update_epochs_per_batch=1 \
+  trainer.train_batch_size=32 \
+  trainer.policy_mini_batch_size=32 \
+  trainer.micro_forward_batch_size_per_gpu=40 \
+  trainer.micro_train_batch_size_per_gpu=40 \
+  trainer.ckpt_interval=10 \
+  trainer.max_prompt_length=512 \
+  generator.sampling_params.max_generate_length=1024 \
+  trainer.policy.optimizer_config.lr=1.0e-6 \
+  trainer.algorithm.use_kl_loss=true \
+  generator.backend=vllm \
+  generator.run_engines_locally=true \
+  generator.weight_sync_backend=nccl \
+  generator.async_engine=true \
+  generator.batched=true \
+  generator.n_samples_per_prompt=5 \
+  generator.gpu_memory_utilization=0.8 \
+  trainer.logger="$LOGGER" \
+  trainer.project_name="gsm8k" \
+  trainer.run_name="gsm8k_llm_as_a_judge" \
+  trainer.resume_mode=null \
+  trainer.ckpt_path="$HOME/ckpts/gsm8k_1.5B_ckpt" \
+  environment.env_class=llm_as_a_judge \
+  environment.skyrl_gym.llm_as_a_judge.model="gpt-4o-mini" \
+  $@
\ No newline at end of file
diff --git a/skyrl-train/skyrl_train/config/skyrl_gym_config/default.yaml b/skyrl-train/skyrl_train/config/skyrl_gym_config/default.yaml
index 37349addfd..a94985f1e5 100644
--- a/skyrl-train/skyrl_train/config/skyrl_gym_config/default.yaml
+++ b/skyrl-train/skyrl_train/config/skyrl_gym_config/default.yaml
@@ -1,10 +1,16 @@
 # @package environment.skyrl_gym
 # number of background workers for env step calls. Set to 0 to disable background workers.
 max_env_workers: 32
+
 text2sql:
   db_path: "/home/ray/default/sql_data"
+
+llm_as_a_judge:
+  model: "gpt-4o-mini"
+  base_url: null  # or a local endpoint: http://localhost:8000/v1
+
 search:
   log_requests: false
   search_url: "http://127.0.0.1:8000/retrieve"
   topk: 3
-  timeout: 30
\ No newline at end of file
+  timeout: 30