SpaceChem Bench: Under the Ice

fusion_2 Medium Fusion Single-reactor Sikutar · SpaceChem Bench report →

Inputs: α Hydrogen (H), β Nitrogen (N). Output: ψ Nitrous Oxide (N2O) ×10. Features: Bonders (4), Fuser.

In SpaceChem Bench, 16 LLMs each had one attempt at this SpaceChem puzzle, with 40 minutes to build a working solution and keep optimizing it, without seeing the community archive. 10 of 16 models solved it. Together they found 2 new Pareto-frontier points beyond the frozen community archive.

10 / 16models solved it
97best LLM cycles (78 community)
2new frontier points

Records

ScoreCommunity bestBest LLMModel
Cycles7897Opus 5.5 · +24%
Reactors11Fable 5.1 Ties record
Symbols1415GPT-6 Astra · +7%

Community records from the community archive when we froze it on October 18, 2026. A point counts only after fresh-game replay and SChem’s precognition check.

Pareto frontier

Pareto explorer

Lower is better ↙
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Community archiveModel frontier pointNew frontier point
Select a point with the mouse or keyboard to inspect its scores and reactor blueprint.

Search over time

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Every model

ModelSolvedBest cyclesBest reactorsBest symbolsNew frontier points
01Gemini 4 ArgonYes1021152
02Opus 5.5Yes97116—
03GPT-6 AstraYes186115—
04GPT-6.1 SolYes187118—
05Sonnet 5.5Yes205131—
06Gemini 3.8 FlashYes238129—
07Haiku 5.5Yes364151—
08Kimi K3.1 ProYes441154—
09Fable 5.1Yes449149—
10Muse Wonder 1.0Yes615146—
11DeepSeek V4.1 FlashNo————
12GLM-5.3No————
13GPT-6 LunaNo————
14Grok 4.7No————
15MiMo-V2.6-ProNo————
16Muse Spark 1.3No————

Best scores can come from different solutions. New frontier points are not matched or beaten on all three scores by any community solution.

Best model solutions

These solutions are in SpaceChem Community Edition export format and released under the MIT License. All of this puzzle’s model solutions are on GitHub and Hugging Face.

Opus 5.5 Fewest cycles

97 cycles · 1 reactor · 42 symbolsfusion_2.97-1-42.txt on GitHub

Layout

α β ψ ω 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 → ↑ → ↑ ← ↑ ↓ ← → ↑ → ↑ ← ↑ ↓ ← S← S→ IN β GRAB GRAB IN β IN β FUSE FUSE B+ B+ IN β B+ IN α CW CW IN β B+ IN β DROP DROP OUT ψ OUT ψ B+ IN α B+ B+ B+

Running in the game

Opus 5.5 solution running on fusion_2 in SpaceChem
SpaceChem Community Edition export (fusion_2.97-1-42.txt)
SOLUTION:Under the Ice,Player,0-0-0
COMPONENT:'drag-fusion-reactor',2,0,''
MEMBER:'instr-start',180,0,128,3,6,0,0
MEMBER:'instr-start',0,0,32,5,3,0,0
MEMBER:'feature-bonder',-1,0,1,1,5,0,0
MEMBER:'feature-bonder',-1,0,1,2,5,0,0
MEMBER:'feature-bonder',-1,0,1,2,4,0,0
MEMBER:'feature-bonder',-1,0,1,2,3,0,0
MEMBER:'feature-fuser',-1,0,1,1,1,0,0
MEMBER:'instr-arrow',0,0,64,1,5,0,0
MEMBER:'instr-arrow',-90,0,64,1,6,0,0
MEMBER:'instr-arrow',0,0,64,2,3,0,0
MEMBER:'instr-arrow',-90,0,64,2,4,0,0
MEMBER:'instr-arrow',180,0,64,3,4,0,0
MEMBER:'instr-arrow',-90,0,64,3,5,0,0
MEMBER:'instr-arrow',90,0,64,6,3,0,0
MEMBER:'instr-arrow',180,0,64,6,6,0,0
MEMBER:'instr-grab',-1,1,128,1,5,0,0
MEMBER:'instr-input',-1,1,128,1,6,0,0
MEMBER:'instr-fuse',-1,0,128,2,3,0,0
MEMBER:'instr-bond',-1,0,128,2,4,0,0
MEMBER:'instr-input',-1,1,128,2,5,0,0
MEMBER:'instr-input',-1,0,128,3,3,0,0
MEMBER:'instr-rotate',-1,0,128,3,4,0,0
MEMBER:'instr-input',-1,1,128,3,5,0,0
MEMBER:'instr-input',-1,1,128,4,3,0,0
MEMBER:'instr-input',-1,1,128,5,3,0,0
MEMBER:'instr-grab',-1,2,128,6,3,0,0
MEMBER:'instr-output',-1,0,128,6,4,0,0
MEMBER:'instr-bond',-1,0,128,6,5,0,0
MEMBER:'instr-arrow',0,0,16,1,5,0,0
MEMBER:'instr-arrow',-90,0,16,1,6,0,0
MEMBER:'instr-arrow',0,0,16,2,3,0,0
MEMBER:'instr-arrow',-90,0,16,2,4,0,0
MEMBER:'instr-arrow',180,0,16,3,4,0,0
MEMBER:'instr-arrow',-90,0,16,3,5,0,0
MEMBER:'instr-arrow',90,0,16,6,3,0,0
MEMBER:'instr-arrow',180,0,16,6,6,0,0
MEMBER:'instr-grab',-1,1,32,1,5,0,0
MEMBER:'instr-input',-1,1,32,1,6,0,0
MEMBER:'instr-fuse',-1,0,32,2,3,0,0
MEMBER:'instr-bond',-1,0,32,2,4,0,0
MEMBER:'instr-bond',-1,0,32,2,5,0,0
MEMBER:'instr-bond',-1,0,32,2,6,0,0
MEMBER:'instr-rotate',-1,0,32,3,4,0,0
MEMBER:'instr-bond',-1,0,32,3,5,0,0
MEMBER:'instr-bond',-1,0,32,5,6,0,0
MEMBER:'instr-grab',-1,2,32,6,3,0,0
MEMBER:'instr-output',-1,0,32,6,4,0,0
MEMBER:'instr-input',-1,0,32,6,5,0,0
MEMBER:'instr-bond',-1,0,32,6,6,0,0

Gemini 4 Argon Fewest reactors★ New frontier point

102 cycles · 1 reactor · 19 symbolsfusion_2.102-1-19.txt on GitHub

Layout

α β ψ ω 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 → ↑ ↓ ← → ← S↓ S← G/D G/D IN β IN β G/D IN α FUSE B+ IN β B+ B+ OUT ψ G/D

Running in the game

Gemini 4 Argon solution running on fusion_2 in SpaceChem
SpaceChem Community Edition export (fusion_2.102-1-19.txt)
SOLUTION:Under the Ice,Player,0-0-0
COMPONENT:'drag-fusion-reactor',2,0,''
MEMBER:'instr-start',90,0,128,2,4,0,0
MEMBER:'instr-start',180,0,32,7,1,0,0
MEMBER:'feature-bonder',-1,0,1,1,5,0,0
MEMBER:'feature-bonder',-1,0,1,1,4,0,0
MEMBER:'feature-bonder',-1,0,1,3,2,0,0
MEMBER:'feature-bonder',-1,0,1,3,3,0,0
MEMBER:'feature-fuser',-1,0,1,1,1,0,0
MEMBER:'instr-arrow',0,0,64,1,1,0,0
MEMBER:'instr-arrow',-90,0,64,1,5,0,0
MEMBER:'instr-arrow',90,0,64,2,1,0,0
MEMBER:'instr-arrow',180,0,64,2,5,0,0
MEMBER:'instr-grab',-1,0,128,1,1,0,0
MEMBER:'instr-input',-1,1,128,1,3,0,0
MEMBER:'instr-input',-1,1,128,1,4,0,0
MEMBER:'instr-grab',-1,0,128,1,5,0,0
MEMBER:'instr-input',-1,0,128,2,1,0,0
MEMBER:'instr-bond',-1,0,128,2,2,0,0
MEMBER:'instr-input',-1,1,128,2,5,0,0
MEMBER:'instr-arrow',0,0,16,1,1,0,0
MEMBER:'instr-arrow',180,0,16,6,1,0,0
MEMBER:'instr-grab',-1,0,32,1,1,0,0
MEMBER:'instr-fuse',-1,0,32,2,1,0,0
MEMBER:'instr-bond',-1,0,32,3,1,0,0
MEMBER:'instr-bond',-1,0,32,4,1,0,0
MEMBER:'instr-output',-1,0,32,5,1,0,0
MEMBER:'instr-grab',-1,0,32,6,1,0,0

Gemini 4 Argon Fewest symbols

175 cycles · 1 reactor · 15 symbolsfusion_2.175-1-15.txt on GitHub

Layout

α β ψ ω 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 → ↑ → ↑ ↓ ← S← S← IN β IN β G/D FUSE IN α IN β G/D OUT ψ B+

Running in the game

Gemini 4 Argon solution running on fusion_2 in SpaceChem
SpaceChem Community Edition export (fusion_2.175-1-15.txt)
SOLUTION:Under the Ice,Player,0-0-0
COMPONENT:'drag-fusion-reactor',2,0,''
MEMBER:'instr-start',180,0,128,3,5,0,0
MEMBER:'instr-start',180,0,32,1,0,0,0
MEMBER:'feature-bonder',-1,0,1,1,5,0,0
MEMBER:'feature-bonder',-1,0,1,1,4,0,0
MEMBER:'feature-bonder',-1,0,1,6,2,0,0
MEMBER:'feature-bonder',-1,0,1,6,3,0,0
MEMBER:'feature-fuser',-1,0,1,1,1,0,0
MEMBER:'instr-arrow',0,0,64,1,2,0,0
MEMBER:'instr-arrow',-90,0,64,1,5,0,0
MEMBER:'instr-arrow',0,0,64,2,1,0,0
MEMBER:'instr-arrow',-90,0,64,2,2,0,0
MEMBER:'instr-arrow',90,0,64,6,1,0,0
MEMBER:'instr-arrow',180,0,64,6,5,0,0
MEMBER:'instr-input',-1,1,128,1,3,0,0
MEMBER:'instr-input',-1,1,128,1,4,0,0
MEMBER:'instr-grab',-1,0,128,1,5,0,0
MEMBER:'instr-fuse',-1,0,128,2,1,0,0
MEMBER:'instr-input',-1,0,128,2,2,0,0
MEMBER:'instr-input',-1,1,128,2,5,0,0
MEMBER:'instr-grab',-1,0,128,6,1,0,0
MEMBER:'instr-output',-1,0,128,6,3,0,0
MEMBER:'instr-bond',-1,0,32,0,0,0,0