open-sci-ref-1.7b-mixturevitae-wo_ot3-100B-4096

MixtureVitae v1 with only OpenThoughts3 removed, 1.7B / 100B tokens, 4096 ctx

Base model (4k).

Why this model exists

Rebuttal experiment for the NeurIPS 2026 submission Strong Post-Training from Permissive, Reasoning-Dominant, Web-Scale Pretraining, addressing reviewer oxw5:

"The OpenThoughts3 traces used in the Phase 2 reasoning stage were already present in MV pretraining, so the unique gain may reflect amplification of seen data rather than general receptivity, and the ablation removes the whole reasoning subset rather than that overlap."

The published MV-noinstruct ablation removes MixtureVitae's entire instruction/reasoning subset (175.1B tokens, 42% of the corpus), so it cannot isolate the OT3 pretrain/post-train overlap. This model removes only OpenThoughts3 — 18.69B tokens, 4.53% of MV — keeping everything else, including the multilingual shards.

Intended comparison:

Data

MixtureVitae v1 (decontaminated), 93 of 96 shards — drops open_thoughts-0/1/2. Weights proportional to shard size, so every kept shard retains its natural share: this is plain MV minus OT3, not a reweighted mixture. 393.92B tokens available; 100B consumed.

Composition: 37 reasoning/instruct (of 40) + 48 non-reasoning + 8 multilingual shards, all GPT-NeoX (uint16, vocab 50304).

Pretraining

1.7B dense, open-sci-ref architecture, GPT-NeoX tokenizer. 100B tokens, 23,842 iters, seq len 4096, RoPE theta 100k, WSD schedule, lr 4e-3, 20% linear cooldown, global batch 1024, warmup 1000. 64 nodes x 4 GH200. Hyperparameters identical to the companion nemotron-hq[-mv_reasoning]-100B-4096 models and to MV-100BT, so all are comparable.

Note: not labelled v0.02 — the published open-sci-ref v0.02 recipe uses global batch 1008 and warmup 25000, and exists only at 300B/1T budgets. This follows the project's 100B convention instead.

Two fixes applied to the released files

• modeling_opensci.py: OpensciModel.forward accepts **kwargs. Recent transformers passes num_items_in_batch from Trainer for loss averaging, and OpensciForCausalLM.forward forwards **kwargs into both self.model(...) and self.loss_function(...). Without this, training raises TypeError: unexpected keyword argument 'num_items_in_batch'.
• config.json: max_position_embeddings cast to int. YaRN writes it as a float (16384.0), and lm-eval uses it as a slice index -> TypeError: slice indices must be integers. Affects the 16k variant.

Language evaluation (open-sci-0.01 suite, lm-eval-harness)

Removing OT3 leaves general language ability intact (+0.52 mean, 8/12 tasks up). That is the point: the base is unchanged, so any Phase-2 difference is attributable to the OT3 overlap rather than to lost general capability. Contrast MV-noinstruct, which removes 42% of the corpus and does degrade.