Show HN: I RL-trained an agent that trains models with RL (for ~$1.3k)

🔓 Everything is open sourced including: the trained agent's weights (LoRA adapter on 🤗 HF), agent harness, task families, reward code, GPU orchestration, tinker RL training scripts, and retro write-ups of every pilot (including the failures). Jump to Getting started ↓

TL;DR:

• I built a pipeline where an AI agent:
  • Is handed a training task ("teach a model to do X")
  • Writes a complete prime-rl training job, including: environment, reward, dataset, hyperparameters.
  • Submits it to real Runpod GPUs for training.
• Leveraging Tinker, I then RL-trained the agent itself, rewarding it when it trained better models.
• Reward climbed from ~0.0 to a ~0.63 peak over 54 training steps. Transferring to a held-out task family it never trained on.

_{An AI in an RL loop, whose action is training AI in an RL loop. (Source: assets/hero.svg.)}

📚 Table of Contents

• 🔁 How it works
  • The episode
• ⚖️ Reward design
• 🧩 Task families
• 📈 Results
  • The reward climbed in two distinct rungs
  • The skill transfers to a held-out task family
  • The agent learned to pick the better base model
• 🖥️ Infrastructure
• 💰 Costs
• 🤗 Model weights
• 🚀 Getting started
• 🔮 Future improvements
• Acknowledgements

🔁 How it works

Two RL loops with two entirely separate training stacks.

Tinker trains the agent. The agent writes verifiers envs, rubrics, and prime-rl configs. prime-rl trains the small model. The inner model's hidden-eval score flows back up as the outer loop's reward.

The episode

_{One episode, end to end. (Source: assets/episode.svg.)}

One episode = one attempt by the trainer agent to produce a valid, high-quality training job for a given task:

1. Task spec — a description of what to train ("teach a small model to resolve multi-hop persona queries"), hard constraint bounds, the eval tool interface, and a handful of dev examples.
2. The agent works — it edits a sandboxed workspace through read_file / write_file / edit_file / list_files, and can call get_baseline_scores to see the untrained base models' scores on the hidden eval.
3. submit_job — triggers a validation probe. Any failures are returned and the agent gets capped retries.
4. Dispatch — a validated job is queued and picked up by a warm pool of Runpod GPU pods, which run GRPO training with prime-rl and score the checkpoint pre/post on the hidden eval.
5. Reward — combines validation efficiency with the trained model's uplift over the best untrained baseline.

The outer loop then RL-trains the agent itself on episode reward, using Tinker. Every outer-loop batch spawns 40 real inner training jobs across up to 16 GPU pods.

⚖️ Reward design

Episode reward is a weighted sum (live weights 0.35 / 0.60 / 0.05):

• Validation — 1.0 for a first-try valid submission, decaying per extra attempt; 0 if the episode never validates. (Separately, the outer loop scores an episode −0.1 when the agent never produces a parseable submission at all. The −1.0 values you'll see in the CSVs are a "no post score" logging sentinel, not a reward.)
• Job quality — a hybrid of the trained model's absolute post-training score and its signed uplift over best_pre, the best untrained model's frozen baseline: 0.25·post + 0.75·uplift_term. A job that dies on the GPU scores 0 here (the episode keeps its validation term).
• Train speed — a small tie-breaker for faster jobs, gated on job success.

_{Note for close readers: the agent-facing prompt (template/INSTRUCTIONS.md) gives the agent a simplified view — the 75/25 uplift/absolute split inside job quality, plus a fewer-attempts nudge — not the full 0.35/0.60/0.05 decomposition. The published adapter was trained against that prompt; the reward actually computed is the one above.}

🧩 Task families

Six families of tasks, deliberately built so that the untrained models struggled without training, and all require multi-step tool use and reasoning:

Five families train the agent; triage is never trained on and serves as the generalisation probe.

📈 Results

Setup: Qwen3.6-35B-A3B trainer agent, LoRA rank 8, lr 4e-5, GRPO with group size 8, up to 16 concurrent GPU pods, ~40 real training jobs per batch. Runs: pilot-7 (10 steps) → 7b (24 steps, warm-started) → 7c (20 steps, warm-started) — 54 steps total.

1. The reward climbed in two distinct rungs

Decomposing the reward shows what was learned, and in what order:

• Rung 1 — process reliability (pilot-7). The entire early gain came from converting validation failures and dead-on-GPU jobs into completed episodes. Job quality stayed flat while total reward rose to ~0.26. Showing GRPO taking the steepest gradient first.
• Rung 2 — making better models (pilot-7b onward). With reliability saturating (~0.75–0.80 validation), job grade rose 0.30 → 0.41 and the hidden-eval post-training score went from ~0.04 noise to a sustained 0.22–0.48. The agent started making better models, not just working ones.

2. The skill transfers to a held-out task family

A task family which the agent never trained on showed performance rises with outer-loop training, then plateaus:

3. The agent learned to pick the better base model & better hyperparams

Early training runs were model-selection blind: 77/79 episodes chose the weaker 0.6B model. After introducing the get_baseline_scores tool and uplift grading, the policy flipped and remained so during training, deepening across the arc: 1.7B share of job-writing episodes went 42% → 95%. It also adopted the exposed [prime_rl] config surface (21% → ~78% of episodes within one warm-start boundary), with a sensible key mix: sampling temperature, optimizer choice, algorithm variant, scheduler, loss.

🖥️ Infrastructure

16x warm GPU pods training at any one time:

Inner loop (the jobs the agent writes):

• Runpod warm-pod fleet — a capped pool (up to 16) of pods, bootstrap-pinned to exact prime-rl + verifiers revisions so every node is a replica; ~2 min from provision to serving. Idle pods are reaped; the queue is file-backed (queued/ → running/ → done/).
• GPU selection is data-driven — a benchmark matrix over GPU × base-model found 2× RTX A5000 wins cost at £0.10/job (~$0.13); preference ladders are walked at provision time to take whatever's in stock.
• What the fleet actually ran on (headline arc, ~1,750 jobs — below the nominal 54 steps × 40 because episodes that fail validation never dispatch a job): A40 64% (340 GPU-train-hours) · RTX 4090 32% (151h) · RTX A6000 3% · RTX A5000 1%. The benchmark cost-winner was rarely in stock, so the ladder spent most of the arc on A40s.
• prime-rl (GRPO) trains the small model; checkpoints are scored pre/post on the hidden eval with vLLM.

Outer loop (training the agent):

• Tinker (Thinking Machines' managed RL API) trains Qwen3.6-35B-A3B with LoRA via tinker-cookbook's importance-sampling GRPO. A control-inversion bridge runs each episode as a background task behind a queue-backed policy, so the cookbook loop drives episodes turn-by-turn while all harness logic (validation retries, nudges, grading) stays unchanged.
• Async off-policy (max_steps_off_policy=2) defeats the straggler barrier — one slow episode no longer gates a whole batch. Zero stale discards across the headline arc.
• Everything is metered. Every LLM call logs tokens and USD; runs/costs.jsonl is a global spend ledger enforced against per-episode budgets.

The whole orchestration runs on a CPU box, rented via Nebius.

💰 Costs

_{Honesty footnote: ~£950 is the headline arc, not the project — the pilots, GPU benchmarking, baseline seeding, and blind alleys that got here (written up in the docs/ retros) cost a few hundred more on top. Benchmark-matrix rows on cold pods ran as high as ~$0.37/job (see benchmarks/REPORT.md); the per-job range above is warm-pool arc jobs. GBP figures at £0.745/$1 (10 Jul 2026).}

🤗 Model weights

The trained trainer agent is on Hugging Face: Danau5tin/ai-trains-ai-trainer.

It's the LoRA adapter (rank 8, ~560MB) from the step-34 checkpoint — the held-out transfer peak in the table above — derived from Qwen/Qwen3.6-35B-A3B and released under Apache-2.0 to match the base model. Load it with PEFT or serve it with vLLM's LoRA support; to run full episodes, drive it through this harness. The model card has usage snippets and honesty notes.

🚀 Getting started

If you'd like to reproduce, or extend. The below will get you there!

# .env at repo root with OPENROUTER_API_KEY=... (and TINKER_API_KEY for outer RL)
uv sync
uv run pytest                                        # fully offline: no network, no keys
uv run at-episode --task examples/tasks/calc_chain_v1_fast.json --model qwen3.6-27b   # run one episode with a frontier agent

Each episode prints reward, token usage, and dollar cost, and writes full artifacts (trajectory, manifest, the agent's workspace) to runs/<run_id>/.

With Runpod + Tinker keys:

uv run at-worker --max-pods 2 --once                 # drain the job queue on real GPUs
uv run python scripts/seed_baselines.py              # freeze eval baselines (required before RL)
uv run python scripts/train_trainer.py smoke=True    # outer RL smoke test

Deeper guides: docs/architecture.md (components and contracts), docs/outer-rl-tinker.md (full RL runbook), docs/gpu-runner-spec.md (compute-provider contract), and the retro series in docs/ — every pilot, including the failures, is written up (pilots 4–5 live inside the eval-integrity retro rather than standalone files).

⚠️ Trust model: agent-written code executes in a timeout-guarded subprocess on the host, not a container. Fine for frontier APIs and your own checkpoints on a template contract; containerise the probe before running untrusted or heavily-RL'd policies.

🔮 Future improvements

• 🔄 Iterative experimentation — today the agent submits one job per episode; the natural next rung is letting it read results and submit follow-up experiments, and / or allowing multiple experiments to be dispatched at the same time, i.e. grading multi-job research taste rather than one-shot job quality.
• 🧠 Richer tasks — only stateless tool-calling envs are exposed today; opening verifiers' other env types would let the trainer agent train stateful coding agents.

Acknowledgements

• Prime-RL: A truly excellent framework for GRPO training. I've used it many times, and the team is great and very helpful!
• Verifiers: A great framework for envs and rubrics.
• Thinking Machines' Tinker: The first time I used it, and it was a great lifestyle choice to not have to manage training infra. Highly recommend.
• Runpod for cheap, scriptable GPU pods.
• The Qwen team for base models small enough to train for pennies and big enough to be worth training.
• The Anthropic team for their incredible coding models (Fable-5 wrote every line of code in this project), and the Claude Code harness.

This project was brilliant fun! An RL loop with an RL loop inside it is confusing, exciting, scary, and points towards a wild future ahead. Thanks for reading!

Dan Austin