JetBrains · Released Sep 20, 2026 · observed 26 Oct 2026
Public-source support evidence
We ran the Q4_K_M GGUF on one Mac; see Hardware notes below. Community MLX weights are available; the architecture is listed in llama.cpp and vLLM.
JetBrains/Mellum2.1-12B-A2.5B-Thinking
Mellum2.1-12B-A2.5B-Thinking is a text generation model published by JetBrains on Hugging Face. We have not written a summary yet; see the model card ↗.
View source model ↗SUPPORT EVIDENCE
The model config architecture is listed in this runtime registry. This is family/architecture evidence only; exact checkpoint loading, model-specific configuration, hardware, and generation were not tested.
Checked 2026-10-27 00:08 UTC
Evidence source ↗The exact model and runtime-specific sources were checked; no positive model-level evidence was established.
Checked 2026-10-26 23:48 UTC
Version v0.40.11
Checked source ↗The exact model and runtime-specific sources were checked; no positive model-level evidence was established.
Checked 2026-10-27 00:28 UTC
Checked source ↗A current public MLX upload with an exact base_model match was observed. Upload availability only; this model was not loaded or hardware-tested.
Checked 2026-10-27 00:08 UTC
Evidence source ↗The model config architecture is listed in this runtime registry. This is family/architecture evidence only; exact checkpoint loading, model-specific configuration, hardware, and generation were not tested.
Checked 2026-10-27 00:08 UTC
Evidence source ↗MLX community uploads may target mlx-vlm; an upload observation does not establish mlx-lm compatibility.
MEMORY ESTIMATES
The summary estimate of about 13 GB is the recommended Q4_K_M quant (8.8 GB observed), from file size × 1.2 + 1.5 GB. Each card is the largest observed quant whose estimate fits that capacity.
Which file should I grab?
Q6_K_L · 11.8 GB observed · about 16 GB ↗About 16 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
Q8_0 · 12.9 GB observed · about 18 GB ↗About 18 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Which file should I grab?
BF16 · 24.3 GB observed · about 31 GB ↗About 31 GB using file size × 1.2 + 1.5 GB. Fit is an estimate; compatibility, speed, context length and hardware have not been tested.
Memory estimates are the observed file size plus fixed headroom (20% plus 1.5 GB runtime allowance); real needs also depend on context length, KV cache and runtime settings. Fit is an estimate; it does not establish runtime compatibility, speed, context length, or hardware performance. Text-weights-only estimates do not include a projector or total vision memory where unknown.
Terms: a quant is a lower-precision version of the weights; GGUF is a file format used by llama.cpp and compatible apps; MLX targets Apple silicon; vLLM is a model-serving engine for NVIDIA GPUs; the KV cache is stored attention state that grows with context length. Terms explained ↗
OBSERVED FILES
Sizes and file groups come from the listed uploader repositories. A size is marked as an estimated fit only for a complete observed GGUF quant group.
| Uploader | Format & quant | Observed size | Estimated fit | Files |
|---|---|---|---|---|
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ2_M | 5.4 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ3_M | 7.2 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ3_XS | 6.3 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ3_XXS | 6.3 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ4_NL | 7.7 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · IQ4_XS | 7.0 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q2_K | 5.5 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q3_K_L | 7.1 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q3_K_M | 6.7 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q3_K_S | 6.1 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q4_0 | 7.0 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q4_1 | 7.7 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q4_K_L | 9.2 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q4_K_M | 8.8 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q4_K_S | 7.9 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q5_K_M | 10.0 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q5_K_S | 9.0 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q6_K | 11.5 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q6_K_L | 11.8 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q6_K_S | 11.1 GB | 16 GB, 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · Q8_0 | 12.9 GB | 24 GB, 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| bartowskibartowski/Mellum2.1-12B-A2.5B-Thinking-GGUF ↗Observed 27 Oct 2026 | GGUF · BF16 | 24.3 GB | 32 GB, 64 GB, 128 GB, 192 GB, 256 GB, 512 GBEstimate only; requires the complete GGUF quant group. | 1 file |
| mlx-communitymlx-community/Mellum2.1-12B-A2.5B-Thinking-6bit ↗Observed 27 Oct 2026 | MLX · Quant unknown | Size unknown | UnknownUnknown: completeness or a complete GGUF quant group was not verified. | 2 files |
CURATED TRACKING
No curated issues verified for this snapshot. An empty list does not mean there are no bugs.
HARDWARE NOTES
We ran the Q4_K_M GGUF (8.07 GB, JetBrains/Mellum2.1-12B-A2.5B-Thinking-GGUF) on an Apple M4 Max Mac, 128 GiB unified memory, macOS 27.0.1, Metal with llama.cpp b11912 (upstream, 961c376) on 26 Oct 2026.
Decode: 155.2 tok/s on a short prompt, 151.0 tok/s on a long prompt (medians of 3 runs).
Peak memory: 8.38 GiB (llama-server footprint).
llama-bench: pp512 2,396.7 tok/s, tg128 157.8 tok/s.
Answer checks: 3 of 4 prompts passed (quick pass/fail sanity checks, not a quality benchmark).
Thinking off (enable_thinking=false), so these are no-think chat numbers for a model built for thinking.
One machine, one run set: temperature 0, 8K context, 1 warm-up plus 3 runs per prompt. Short prompt is 24 tokens; long prompt is 1,484 tokens (each model counts with its own tokenizer). Weights were loaded from an external USB drive with mmap off; load time is not published for this run. Your speed will differ with hardware, context length and settings.
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