This is a Plain English Papers summary of a research paper called daVinci-Dev: Agent-native Mid-training for Software Engineering. This is a Plain English Papers summary of a research paper called daVinci-Dev: Agent-native Mid-training for Software Engineering daVinci-Dev: Agent-native Mid-training for Software Engineering . Overview Large language models have moved beyond simple code generation to becoming autonomous software agents that navigate and modify entire codebasesThe research introduces agentic mid-training, a method to teach models foundational agent behaviors using realistic development workflows at scaleTwo types of training data drive the approach: contextually-native trajectories that show the complete information agents see, and environmentally-native trajectories from actual executable repositoriesThe models achieve 56.1% and 58.5% resolution rates on SWE-Bench Verified using just 73.1 billion tokens—less than half the tokens used in previous approachesThis work demonstrates that training methods can outperform earlier software engineering mid-training recipes while being more efficient Large language models have moved beyond simple code generation to becoming autonomous software agents that navigate and modify entire codebases The research introduces agentic mid-training, a method to teach models foundational agent behaviors using realistic development workflows at scale agentic mid-training Two types of training data drive the approach: contextually-native trajectories that show the complete information agents see, and environmentally-native trajectories from actual executable repositories The models achieve 56.1% and 58.5% resolution rates on SWE-Bench Verified using just 73.1 billion tokens—less than half the tokens used in previous approaches This work demonstrates that training methods can outperform earlier software engineering mid-training recipes while being more efficient Plain English Explanation Think of training a software engineering agent like teaching someone to work in a real codebase. The old approach was to wait until the very end and use expensive trial-and-error reinforcement learning to fix mistakes. This new research asks: what if we train agents on realistic development scenarios from the start? The key insight is that there's a gap between how training data looks and how agents actually work. Training data sits static on a hard drive. Real agent work is dynamic—the agent runs a test, sees it fail, reads the error message, modifies code, and tries again. That feedback loop matters enormously. The researchers created two complementary types of training trajectories. Contextually-native trajectories work like having a complete transcript of everything an agent observes while solving a problem—every file it reads, every tool it uses, every decision it makes. This gives broad coverage and variety. Environmentally-native trajectories go deeper by collecting data from real executable repositories where observations come from actually running tools and tests, not simulated ones. Contextually-native trajectories Environmentally-native trajectories This approach treats the training phase itself as teaching agents how to behave like agents, rather than waiting until deployment to figure that out. The 32B and 72B parameter models reached 56.1% and 58.5% resolution rates respectively, outperforming previous methods while using significantly fewer training tokens. Key Findings The 32-billion-parameter model achieved a 56.1% resolution rate on SWE-Bench VerifiedThe 72-billion-parameter model reached 58.5% resolution rate on the same benchmarkThe approach used only 73.1 billion tokens during mid-training, less than half what the previous open software engineering mid-training method requiredAgent-native data—combining contextually-native and environmentally-native trajectories—proved superior under two different post-training configurationsThe method outperformed Kimi-Dev despite using substantially fewer resources The 32-billion-parameter model achieved a 56.1% resolution rate on SWE-Bench Verified The 72-billion-parameter model reached 58.5% resolution rate on the same benchmark The approach used only 73.1 billion tokens during mid-training, less than half what the previous open software engineering mid-training method required Agent-native data—combining contextually-native and environmentally-native trajectories—proved superior under two different post-training configurations The method outperformed Kimi-Dev despite using substantially fewer resources Kimi-Dev Technical Explanation The core contribution involves a systematic framework for agentic mid-training that bridges the distribution gap between static training corpora and dynamic agent execution environments. Rather than treating mid-training as a generic language modeling task, the researchers designed data synthesis to capture authentic agentic workflows. agentic mid-training The two-trajectory approach creates complementary supervision signals. Contextually-native trajectories preserve the full information flow an agent experiences during problem-solving, including repository structure, file contents, tool outputs, and reasoning steps. This mirrors what the agent actually observes. Environmentally-native trajectories add depth by sourcing data from executable repositories where the agent's observations come from genuine tool invocations—running tests, executing commands, receiving actual error messages—rather than curated examples. The training methodology works with an aligned base model and agentic scaffold, meaning the researchers used carefully prepared foundational models designed for agent behavior. This dual-trajectory approach reduces the distribution mismatch by training on data that actually reflects how agents operate when deployed in real repositories. foundational models The efficiency gains—using less than half the tokens of previous methods—suggest that the composition and quality of training data matters more than raw quantity. By designing data that matches agent behavior patterns rather than generic code patterns, the training becomes more signal-rich. The evaluation on SWE-Bench Verified demonstrates these gains transfer to challenging real-world software engineering tasks. Critical Analysis The paper focuses heavily on the data synthesis principles but provides limited analysis of failure cases or where the approach breaks down. Understanding which types of problems or repositories remain difficult could guide future work. The comparison primarily centers on a single baseline (Kimi-Dev), so broader comparisons with other mid-training approaches would strengthen the evidence. The reliance on executable repositories for environmentally-native trajectories introduces practical constraints—not all problems may have reliable test suites or executable environments. The paper doesn't address how the approach scales to codebases with weaker observability or test coverage, which represents a significant portion of real-world software projects. Additionally, the token efficiency claim deserves scrutiny. While using 73.1 billion tokens versus more is impressive, the absolute performance gap between this work and post-training-only baselines remains unclear from the abstract. The relationship between mid-training quality and post-training effectiveness—whether better mid-training enables lighter post-training or merely provides marginal gains—needs deeper examination. The agentic scaffold design itself appears central to success but receives minimal description. The generalizability to different scaffold architectures or without scaffolding remains open. Finally, while SWE-Bench Verified provides a rigorous evaluation, the benchmark covers a specific class of problems; performance on other software engineering tasks (code review, documentation generation, refactoring) remains unexplored. Conclusion This research makes a compelling case that agentic mid-training deserves investment despite its computational demands. By treating training data as a faithful representation of how agents operate in real environments, the approach achieves strong performance while actually reducing the total compute spent versus previous methods. The conceptual contribution—recognizing that distribution alignment between training and deployment matters for agents just as much as it does for other machine learning systems—has immediate practical value. agentic mid-training The work opens avenues for more efficient software engineering agent development by shifting resources earlier in the pipeline. Rather than betting everything on expensive reinforcement learning post-training, this method establishes stronger foundations during mid-training where diverse data makes the approach more scalable. For teams building production agents, the efficiency gains suggest that investing in higher-quality agent-native training data yields better returns than simply training larger models or running longer post-training cycles. software engineering agent development If you like these kinds of analyses, join AIModels.fyi or follow us on Twitter. If you like these kinds of analyses, join AIModels.fyi or follow us on Twitter. 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