What is ThinkingCap?
ThinkingCap is BottleCap AI's fine-tune of Qwen3.8-27B for token-efficient reasoning: it cuts thinking tokens by ~37% on average (11–66% depending on benchmark) while holding accuracy near the base model (85.8% vs 86.6% average). It shines on long-context retrieval, where it cuts reasoning by 39% with +2.3pp accuracy.
Original model card: bottlecapai/ThinkingCap-Qwen3.8-27B (Polyform Small Business license).
Given two models sharing an identical architecture:
W_base = Qwen3.8-27B weightsW_think = ThinkingCap weightsΔ = W_think − W_base ← fine-tune signal only, base cancels outΔ ≈ U_r Σ_r V_rᵀ (truncated SVD, rank r = 32)lora_A = Σ_r^½ V_rᵀ , lora_B = U_r Σ_r^½
Pipeline (all computed on CPU in float32, then stored as the GGUF/PEFT adapter):
- Architecture check — both repos expose the same 1,199 tensor names and identical shapes (
qwen3_5_text, 64 layers, hidden 5120, intermediate 17408, MTP head, vocab 248320). No remapping needed.
- Norm scan — Δ computed for all 866 non-visual tensors. 257 tensors had
‖Δ‖ ≥ 0.05; everything else was within fine-tune noise (lm_head and embed_tokens deltas were < 0.001, so embeddings are already covered by Qwen's).
- Exact truncated SVD at uniform rank 32 on those 257 tensors → 257
lora_A/lora_B pairs.
- Reconstruction validation — for a 40-tensor sample, the adapter's implied delta
B@A vs the true delta Δ: mean relative error 0.88.
Important honesty note: this is an approximation
ThinkingCap is a diffuse fine-tune, not a low-rank edit. Even full-rank energy analysis shows:
Table with columns: rank, fraction of Δ energy captured (largest tensor per module)| rank | fraction of Δ energy captured (largest tensor per module) |
|---|
| 16 | 21–29% |
| 32 | 27–33% |
| 64 | 34–37% |
| 128 | 42–44% |
| 256 | 47–48% |
So this LoRA captures the dominant components of the token-efficiency fine-tune (the large singular directions that carry most of the behavioural change), but it is not an exact merge. Expect: noticeably shorter reasoning traces on Qwen3.8-27B, with some loss of ThinkingCap's fine-grained calibration. If you need bit-level fidelity, use the original full model instead.
Table with columns: Target, Tensor count, Δ norm range, energy retained @ r=32| Target | Tensor count | Δ norm range | energy retained @ r=32 |
|---|
mlp.gate_proj | 64 | up to 0.186 | ~29% |
mlp.up_proj | 64 | up to 0.184 | ~27% |
mlp.down_proj | 64 | up to 0.092 | ~16% |
|
Files
Table with columns: File, Format, Notes| File | Format | Notes |
|---|
adapter_model.safetensors | PEFT LoRA | r=32, alpha=32, float32, 257 pairs |
adapter_config.json | JSON | Standard PEFT config, base_model: Qwen/Qwen3.8-27B |
thinkingcap_qwen3.8-27B_svd_lora.gguf | llama.cpp LoRA GGUF | load with --lora against a Qwen3.8-27B GGUF |
extraction_stats.json |
Usage
llama.cpp (GGUF)
llama-cli -m Qwen3.8-27B.gguf \ --lora thinkingcap_qwen3.8-27B_svd_lora.gguf \ -p "..."
Or scaled (0.5 = halfway back toward stock Qwen behaviour):
llama-server -m Qwen3.8-27B.gguf \ --lora-scaled thinkingcap_qwen3.8-27B_svd_lora.gguf:0.5 \ --n-gpu-layers 99 --ctx-size 32768 -fa on
from peft import PeftModelfrom transformers import AutoModelForCausalLM, AutoTokenizer base = "Qwen/Qwen3.8-27B"model = AutoModelForCausalLM.from_pretrained(base, torch_dtype="bfloat16", device_map="auto")model = PeftModel.from_pretrained(model, "hotdogs/thinkingcap_qwen3.8-27B_svd_lora")
License
Derivative of bottlecapai/ThinkingCap-Qwen3.8-27B, which carries the Polyform Small Business License 1.0.0. This adapter is intended for non-commercial research/evaluation use; commercial use should respect the upstream license. Base model Qwen3.8-27B is Apache-2.0.