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abstract indexed · arXiv 2610.22019 · updated 2026-10-18

Priming Base Models for Agentic Post-Training: An Open Midtraining Recipe

First page of Priming Base Models for Agentic Post-Training: An Open Midtraining Recipe
From the original paper · arXiv 2610.22019Page 1. Select the image to read the PDF.

The method inserts a midtraining stage between pretraining and post-training, replacing the practice of going directly from short-context pretraining to synthetic SFT and long RL stages. It costs hundreds of billions of tokens of training at 256K context on large frontier-scale base models, which requires cluster-scale compute and curated repository-scale data pipelines far beyond a single 24 GB GPU or a limited API budget. It can fail because base-model proxy metrics did not correlate with post-training outcomes, so recipe validation requires repeated fixed SFT runs, and gains may not transfer to smaller or differently pretrained models.

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Compare against

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  3. Run the baseline and the proposed change on identical inputs. Keep other settings fixed and repeat paired runs to expose variation.
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What to measure

Correct patches, regression failures, human repair time, and total cost per accepted change.

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Why it was shortlisted

The technical change, research area, and reason it entered the archive.

recommendation
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research area
coding agents
technical change
Long-context agentic midtraining before post-training
published
2026-10-15

The recipe requires cluster-scale midtraining compute and proprietary-scale data mixtures that a constrained team cannot execute, so it is relevant as context on how frontier coding agents are built but not adoptable or testable at small scale.

About the technical core

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Claims and evidence

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  1. claim 01Paperraft inference
    Read the brief interpretation

    The method inserts a midtraining stage between pretraining and post-training, replacing the practice of going directly from short-context pretraining to synthetic SFT and long RL stages. It costs hundreds of billions of tokens of training at 256K context on large frontier-scale base models, which requires cluster-scale compute and curated repository-scale data pipelines far beyond a single 24 GB GPU or a limited API budget. It can fail because base-model proxy metrics did not correlate with post-training outcomes, so recipe validation requires repeated fixed SFT runs, and gains may not transfer to smaller or differently pretrained models.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source
  2. claim 02Paperraft inference

    On Nemotron 3.5 Lightning, 500B midtraining tokens raise SWE-bench Verified from 60.7 to 64.5 and SWE-bench Multilingual from 55.8 to 62.8 after identical SFT; on Nemotron 3.5 Super, 280B tokens raise DeepSWE from 11.7 to 15.7.

    This is a Paperraft inference. It is not pinned to a verified PDF passage.

    Inspect the source

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quality

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compute and memory

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latency

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operations

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software compatibility

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security

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data and training

Still unknown

What data preparation or training is required, and is it included in the cost?

reproducibility

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Continue the investigation

A reading guide for coding agents.

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What to inspect

Does the evaluation use held-out repositories and tests the agent cannot modify?

Plan a fair comparison

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Questions for adoption

How many tasks pass independent tests, and what is the cost per accepted change?

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Inside the paper

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Provisional research brief updated 2026-10-18. Paperraft has not reproduced this experiment.

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arXiv 2610.22019

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