nkthebass/tinybrainbot-320mV2-instruct

TinyBrainBot 320M V2 — Instruct

A ~326M-parameter decoder-only language model, trained from scratch on ~10B tokens and then supervised-fine-tuned for chat / instruction following. This is the instruct model.

• Base model: tinybrainbot-320mV2-base (full pretraining details there).
• Successor to the 303M V2 instruct.

TL;DR: A compact general-purpose assistant trained from scratch on ~10B tokens, with an added conversational + in-context-recall fine-tune (robust multi-turn chat, diverse instruction phrasings, remembers facts stated earlier in the conversation). It matches/beats Pythia-410M on general benchmarks (on far fewer training tokens) and sweeps GPT-2-124M, follows instructions, and has 2–3-digit arithmetic far stronger than its GSM8K reasoning score would suggest (94–99% on 2–3-digit addition) — though it hits a clear length-generalization wall beyond 3 digits. It is not math-specialized.

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Model details

Parameters	325,899,264 (~326M)
Architecture	Decoder-only transformer, pre-norm, RMSNorm, SwiGLU MLP, RoPE
Hidden size	1024
Layers	26
Attention heads	16 (query) / 4 KV heads (grouped-query attention)
FFN size	2816
Context length	1024
Vocabulary	32,000
Tokenizer	tbb-32k-v2 — 32k BPE (67% English / 20% code / 13% math), with reserved <think>/</think> special tokens
Precision	trained in fp16 with an fp32 master copy (autocast)

Usage

Prompt with the chat format:

<|user|>
{user message}
<|end|>
<|assistant|>
{assistant reply}
<|end|>

Example (greedy):

<|user|>
What is the capital of France?
<|end|>
<|assistant|>
Paris.
<|end|>

The model gives concise direct answers and shows worked steps for arithmetic.

Conversational + recall update

This release adds a conversational + in-context-recall fine-tuning pass on top of the base instruct SFT. It:

• answers open-ended imperatives robustly — list all the planets in the solar system → Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.;
• handles multi-turn chat and in-context recall (state a fact early, ask about it later);
• stays consistent across the F16 GGUF (LM Studio / Ollama / llama.cpp) and the fp16 transformers weights.

(An earlier build gave terse/empty answers to some imperative phrasings through the GGUF export. That was a real tokenization mismatch in the export — not a capacity limit. This release fixes it two ways: the conversational pass makes the model robust to it, and the F16 GGUF now sets tokenizer.ggml.add_space_prefix=false + ships a leading-space chat template so llama.cpp tokenizes the chat format token-for-token identically to the native tokenizer, per llama.cpp #23840.)

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Training procedure

Pretraining (blue, ~10B tokens) → instruct SFT (orange, from step 51k) → conversational + recall SFT (green, steps 52k–55k, final loss ~0.5).

Pretraining (base)

Pretrained from scratch on 10.03B tokens (51,000 steps, WSD schedule, peak LR 6e-4, two-phase broad → quality-anneal, final loss 1.436) across 2× Tesla V100-PCIE-16GB with PyTorch DDP (gloo), fp16 autocast + fused AdamW. Full pretraining details and the 13-source data mix are documented on the base model card.

Supervised fine-tuning (this model)

Hyperparameter	Value
Steps	~1,433 (resumed from base @ 51,000)
Tokens	~94M
LR	1.5e-5, constant
Warmup	100 steps
Global batch	4 micro × 8 grad-accum × 2 GPUs × 1024 seq
Loss masking	assistant-only
Best checkpoint	step 52,000 (selected on eval, not last)

SFT data mix (sampling weights; sum = 9.5; math ≈ 15.8% of the mixture):

Source	Weight
longdef-sft (~16k long / multi-step answers)	2.0
smoltalk	2.0
math-v2 (~70k verified worked examples)	1.5
qa-distill	1.0
lamini-instructions	1.0
soda-dialogues	1.0
greetings	0.5
reasoning-distill	0.5

math-v2 is ~70k programmatically-generated, tolerance-verified arithmetic worked examples (multiplication / division / decimals, with the final answer checked). It appears in both pretraining and SFT — see the note below.

On where the arithmetic comes from: the base and instruct models score almost identically on the GPT-3 Arithmetic suite (aggregate 31.4% vs 31.2%). That base/instruct parity suggests most arithmetic computation was acquired during pretraining, while SFT mainly shaped instruction-following and response format (the one sub-task where SFT clearly helps is composite / order-of-operations, 7.0% vs 3.7%). Pretraining also delivered far more math tokens in absolute terms — on the order of ~215M vs ~15M — despite SFT's higher math proportion.

Conversational + recall fine-tuning (final stage — this release)

A further SFT pass continued from the instruct checkpoint (step 52,000 → 55,000) to make the model a robust multi-turn conversationalist, teach in-context recall, and fix brittle behavior on open-ended instruction phrasings.

Hyperparameter	Value
Steps	3,000 (resumed from instruct @ 52,000)
LR	1.5e-5, constant (WSD, decay-fraction 0)
Global batch	2 micro × 16 grad-accum × 2 GPUs × 1024 seq
Loss masking	assistant-only
Final loss	~0.5

Data mix (sampling weights):

Source	Weight
convo-recall (6k multi-turn in-context-recall dialogues)	2.5
convo-core (4k instruction-phrasing + small-talk)	2.5
smoltalk	1.5
math-v3	0.75
longdef-sft	0.75
greetings	0.5
qa-distill	0.5

convo-recall and convo-core are programmatically generated: convo-recall teaches in-context memory (the user states facts early — name / city / pet / counts — then asks about them later), and convo-core covers diverse instruction verbs ("list all / name / give me / what are the …") over closed sets with correct complete answers, plus natural small-talk. Alongside the conversational gains, this pass makes the model robust to the SPM normalization that the GGUF/HF exports drop — so it now behaves consistently in llama.cpp / LM Studio / Ollama and in transformers, instead of degrading on some phrasings through the export.

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Evaluation

Measured on our own log-likelihood MC harness (lm-eval style, fixed seed). Headline metric = acc_norm for HellaSwag/ARC/OpenBookQA, acc for WinoGrande/MMLU. Reference values are published lm-eval approximations — treat gaps under ~±2 points as ties.

vs the previous 303M instruct (full test sets)

Benchmark	n	320M V2 instruct	303M instruct
HellaSwag	10042	34.5	30.7
ARC-Easy (acc_norm)	2376	49.3	47.6
ARC-Easy (raw acc)	2376	57.0	51.0
ARC-Challenge	1172	27.6	27.6
OpenBookQA	500	31.8	29.0
WinoGrande	1267	53.3	52.2
MMLU	14042	28.0	27.1

→ 5 wins, 1 tie, 0 losses over the previous generation.

vs reference models (headline metric)

Benchmark	320M V2 instruct	GPT-2-124M	Pythia-410M	SmolLM-360M
HellaSwag	34.5	31	34	54
ARC-Easy	49.3 (57 raw)	44	52	70
ARC-Challenge	27.6	22	24	37
OpenBookQA	31.8	29	30	42
WinoGrande	53.3	52	53	57
MMLU	28.0	26	25	34

→ Sweeps GPT-2-124M; ~5 wins + 1 draw vs Pythia-410M. SmolLM-360M (trained on ~600B aggressively-filtered tokens) remains the frontier for this size.

Training efficiency. These results come from ~10B pretraining tokens — roughly an order of magnitude fewer than the Pythia suite's ~300B. The Pythia-410M parity is therefore best read as a token-efficiency result (curated data + quality anneal) rather than a scale win.

Math — computation vs reasoning

The model was trained on arithmetic computation, not word-problem reasoning — the two benchmarks below show that split clearly.

GSM8K (grade-school word problems, full 1319-problem test, zero-shot chain-of-thought):

Model	GSM8K
GPT-2-124M	~0%
320M V2 instruct	0.53%
Pythia-410M	~1–2%
SmolLM2-360M-Instruct	~3–5%

→ At the floor for a general-purpose model of this size and training mix; stronger sub-1B math-specialized models can score substantially higher. GSM8K rewards multi-step semantic reasoning, which this recipe did not target.

GPT-3 Arithmetic (Brown et al. 2020 protocol, exact-match, n=300/sub-task):

Sub-task	Accuracy
2-digit addition	99.0%
3-digit addition	94.0%
2-digit subtraction	49.3%
3-digit subtraction	42.7%
4-digit addition / subtraction	0.3% / 0.3%
5-digit addition / subtraction	0.0% / 0.0%
2-digit multiplication	21.7%
single-digit composite (order of ops)	7.0%
Aggregate (all 10 sub-tasks)	31.4%

→ Strong through 3 digits, then a hard wall. 2–3-digit addition is near-solved (94–99%, with correct carrying), but 4+-digit accuracy collapses to 0%: the model executes a fixed **3-column** addition routine and silently drops the higher place values — a length-generalization limit tied to the training distribution (math-v2 operands are ≤3 digits), not truncation (generations complete normally and end with a stated answer). Subtraction sits ~42–50% — it handles a−b when a>b but drops the sign on negative results. 2-digit multiplication ~22%; single-digit composite (order of operations) ~7%.

How to read this: the GPT-3 Arithmetic suite mainly probes exact symbolic computation and short-range algorithmic generalization; it should not be interpreted as evidence of strong mathematical reasoning (see GSM8K above). The two results together are the point: strong at computing, weak at reasoning.

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Intended use & limitations

Intended use: a capable general chat assistant at ~326M scale, on-device / low-resource deployment, research on small-model SFT, and arithmetic computation.

Limitations:

• Math reasoning (word problems, GSM8K/MATH) is at the floor — the model computes but does not reason through multi-step problems.
• Negative-result subtraction is unreliable (drops the sign).
• WinoGrande and MMLU sit near the random floor — consistent with the capacity and data limits of a ~326M model under this training recipe.
• Trained predominantly on English; 1024-token context; no RLHF/safety tuning — outputs may be incorrect or inappropriate and should not be relied upon unchecked.

Hardware & framework

2× NVIDIA Tesla V100-PCIE-16GB · Windows · PyTorch DDP (gloo) · fp16 autocast (fp32 master) · fused AdamW · custom TinyBrainBot trainer.