How do you choose the data mixture for pretraining an LLM, and what does domain reweighting buy you?

The ratio of web, code, books, and math in pretraining quietly decides downstream skills. The signal is knowing how mixtures are chosen, why upsampling helps, and how methods like DoReMi automate it.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.

The ratio of web, code, books, and math in pretraining quietly decides downstream skills. The signal is knowing how mixtures are chosen, why upsampling helps, and how methods like DoReMi automate it.

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