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Reinforcement fine-tuning (RFT) trains a model by having it generate answers, scoring those answers with a grader, and updating the model to make high-scoring answers more likely, rather than teaching it to copy example outputs.
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Aperçu
It matters because it can improve reasoning on tasks where a correct answer is easy to check but hard to demonstrate step by step. Its main risk is reward hacking, where the model learns to please the grader instead of solving the task.
Plongée profonde
Standard supervised fine-tuning shows the model an input and the exact output you want, and trains it to imitate. That works when you can write good target outputs, but it teaches the surface form of answers rather than the process of reaching them. Reinforcement fine-tuning works differently. For each training prompt, the model samples one or more candidate answers. A grader assigns each a score, often between 0 and 1. The training algorithm then adjusts the model so that answers scoring above average become more likely and those below average less likely. Over many rounds, the model keeps the reasoning patterns that earn reward. Graders come in a few kinds. Exact or string-match graders check whether a final answer equals a reference. Programmatic graders run code, such as unit tests or a numerical tolerance check. Model-based graders use another language model with a rubric to judge qualities that are hard to check mechanically. Graders can also give partial credit, which gives the model a smoother signal. RFT suits tasks with verifiable or reliably gradable answers where experts agree on what is correct: classification with defined labels, maths, code, structured extraction, and some specialised judgement tasks. It is a poor fit where quality is subjective and graders disagree. OpenAI previewed a reinforcement fine-tuning service in December 2024, and reasoning models more broadly have been trained with reinforcement learning on verifiable rewards. The central failure mode is reward hacking. The model optimises the grader, not your intent. If a grader only checks the final line, the model may produce a correct-looking final line with broken reasoning. If a model grader likes length or confident wording, outputs drift toward those traits. A common misconception is that a higher training reward means a better model; it only means a better score from that grader.
Impact stratégique
Coût et budget
Les décisions en matière d'architecture déterminent les performances et les coûts d'exploitation pendant des années.
Décisions plus claires
La formation technique aide les équipes à choisir la bonne pile, pas seulement la plus récente.
Contrôle qualité
De meilleurs choix d’ingénierie réduisent les incidents de fiabilité en production.
The Future of Reinforcement Fine-Tuning with Graders
Reinforcement learning on gradable tasks has become an important part of how reasoning models are trained, and hosted services are making RFT available to smaller teams. Progress is likely to depend less on the training algorithm and more on grader quality, since a model can only become as good as the signal it is optimised against. Research into more robust graders, multiple independent graders and better detection of reward hacking is active. For most organisations, the practical question will remain whether they can define correctness clearly enough to grade it.
Mise en œuvre dans le monde réel
A tax software team trains a model to classify expense items into the correct category code, with a grader that checks the predicted code against a labelled answer.
A company building a coding assistant rewards generated functions by running them against unit tests, so the reward reflects whether the code actually works.
A medical research group trains a model to rank likely genes given a list of symptoms, with a grader that gives partial credit when the correct gene appears near the top of the ranking.
A team uses a model-based grader to score customer email replies for accuracy and tone, then discovers the policy has learned to add flattering phrases the grader over-rewards.
Risques et garde-fous
L’optimisation d’un benchmark peut masquer des faiblesses plus larges du système.
Les coûts d’infrastructure et de maintenance sont souvent sous-estimés.
Les lacunes en matière de sécurité et d’observabilité peuvent se creuser à mesure que les systèmes deviennent plus complexes.
Feuille de route de mise en œuvre
Définissez les objectifs de latence, de qualité et de coût avant la mise en œuvre.
Benchmark dans des conditions de charge et de données réalistes.
Surveillance des instruments pour détecter les erreurs, la dérive et l'impact sur l'utilisateur.
Préparez les chemins de restauration et de réponse aux incidents avant la mise à l’échelle.
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Questions fréquemment posées
What is Reinforcement Fine-Tuning with Graders?
Reinforcement fine-tuning (RFT) trains a model by having it generate answers, scoring those answers with a grader, and updating the model to make high-scoring answers more likely, rather than teaching it to copy example outputs. It matters because it can improve reasoning on tasks where a correct answer is easy to check but hard to demonstrate step by step. Its main risk is reward hacking, where the model learns to please the grader instead of solving the task.
How does reinforcement fine-tuning differ from supervised fine-tuning?
Supervised fine-tuning imitates targets; RFT samples answers, scores them with a grader and reinforces high-scoring ones.
Which grader type would you use to check that generated code actually works?
Programmatic graders can execute code against tests, directly measuring whether it works.
Which task is the poorest fit for RFT according to the guide?
RFT needs a reliable grade. When experts disagree about what is correct, the reward signal is noisy.
In Reinforcement Fine-Tuning with Graders: what is reward hacking?
Reward hacking happens when optimisation exploits weaknesses in the grader, raising scores without improving true quality.
Why do prompts where every sample gets the same score provide little learning signal in group-relative methods like GRPO?
GRPO uses relative scores within a group as the advantage. If all scores match, there is no difference to learn from.
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