STEALTHMARK · HEAD TO HEAD

All comparisons ↗

Muse Spark Open vs Callstack Apex

Callstack Apex leads Muse Spark Open by 5.4 points on StealthMark, 49.5 to 44.1. It leads on 5 of the 8 benchmarks with results for both and Muse Spark Open on 3, including Latch. Pixel Canary scores higher on Newton's Mirror, with its largest category advantage in camera and placement.

See the difference ↘
All results ↗
Model guide ↗

Overall StealthMark

44.1/100Overall rank 29/53
49.5/100Overall rank 18/53

General Intelligence

42.6/100
40.4/100

Visual Intelligence

46.6/100
59.6/100

Reasoning efficiency

On every task, result quality and reasoning tokens are each compared with all measured models and weighed equally. Each dot is one model.

Single-step reasoning Result quality weighed against reasoning tokens on a single problem

Multi-step reasoning Result quality weighed against reasoning tokens across connected steps, as in agentic workflows

  • Muse Spark Open

Open or local

BENCHMARK BY BENCHMARK

Where each model leads

  • Muse Spark Open
  • Callstack Apex
  • Other models
  • Median

DATASHEET

Specs and pricing

Muse Spark Open takes 4× more context and runs 41% faster in our speed test. Callstack Apex scores higher on StealthMark and is 42% cheaper per output token.

  • Muse Spark Open
  • Callstack Apex
  • Other models
  • Median
PricePer 1M output tokens, input below
Muse Spark Open: $4.25$1.25 inputCallstack Apex: $342% cheaper$0.50 input
Context windowTokens per request, max output below
Muse Spark Open: 1M4× larger1M max outputCallstack Apex: 256K
Output speedTokens per second, our measurement
Muse Spark Open: 36141% fastertokens/sCallstack Apex: 255tokens/s
SizeTotal and active parameters
Muse Spark Open: 816B42B activeCallstack Apex: Not disclosed
Developer
MetaCallstack
Released
15 Oct 20261 Oct 2026
Origin
United StatesPoland
Input → output
Text, image, audio, video → textText → text
Architecture
Sparse mixture-of-experts Transformer with perception encoders; 62 decoder layers, 256 experts with 8 selected per token, grouped-query attention and sliding-window/full-attention layers.Qwen foundation with Callstack domain post-training for React and React Native

Full datasheets, every price and sourceMuse Spark Open ↗Callstack Apex ↗

Anticipating threats and planning ahead. Collect coins while avoiding ghosts. Ghosts move before the player each turn, and collisions cost a life. 3 levels in sequence, up to 66 turns in total. Earlier moves and outcomes carry forward, testing learning across levels.

Muse Spark Open 29.4/100Rank 34/47

Survived 0 of 3
Foresight: complete playing field
Level 38 ptsTurn 15 / 20

Points per level

LevelMuse Spark OpenCallstack Apex
Level 1Second Thoughts
4 ptsOut of lives
No run
Level 2Pressure Pot
9 ptsOut of lives
No run
Level 3Hide or Flight
8 ptsOut of lives
No run

Cooperative planning and learning from experience. Coordinate two robots to push numbered cores onto matching sockets. Pressure plates hold doors open; moving either robot uses one turn. 5 levels in sequence, up to 152 turns in total. Earlier moves and outcomes carry forward, testing learning across levels.

Muse Spark Open 75.7/100Rank 12/48

Cleared 5 of 5
Latch: complete playing field
Level 519.6 ptsTurn 32 / 40

Callstack Apex 100.0/100Rank 40/481 of 5 levels

1 of 5 played
Latch: complete playing field
Level 15.2 ptsTurn 6 / 12

Points per level

LevelMuse Spark OpenCallstack Apex
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
9.8 ptsCleared
Pending
Level 3Relay vault
19.2 ptsCleared
Pending
Level 4Passing bay
17.8 ptsClearedFinished early · 1 beacon left
Not played
Level 5Second thoughts
19.6 ptsCleared
Not played

Newton's Mirror

Same task instructions

Physics, perspective and recursive reflections, tested together. Explore the test ↗

The judgment

Muse Spark Open

The airborne black blob and deformed paint support the broad contact sequence, although cyan attachment and wheel-directed transport remain partial. The sphere and black blob have substantial framing errors. The dominant limitation is the largely absent mirror system: faint wall circles and isolated highlights provide little evidence of recursive room geometry or curved nested reflections. Oversized compact paint features and diffuse material treatment further limit credit.

Callstack Apex

The principal sphere placement and paint contact sequence are supported. Isolated sphere and panel images provide limited optical structure, but missing lateral chains and side-floor continuations prevent a coherent repeating mirror room. The main and reflected spheres lack ordered curved nested imagery, while sparse planar emitter images and incomplete spherical emitter mapping leave most of the reflection system unsupported.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
State at 600 ms14.0/2520.0/25
Camera and placement6.0/1513.0/15
Reflections8.0/12010.0/120
Materials and scale3.5/107.0/10
Floor-damage reward0.0/100.0/10

Benchmark task

A spinning metal sphere and paint in a mirrored room test physical reasoning, perspective and consistency across repeated reflections.

Selfie

Different task instructions

Visual construction and creative interpretation.

The judgment

Muse Spark Open

The rounded silhouette and asymmetric expression make an appealing baby elephant, supported by a quiet background and grounding shadow. The protective action remains difficult to read: forefeet cannot be confidently traced into a grip, and seed contact is crowded by fine lines. Controlled simple shapes provide charm, but limited anatomical clarity, shading and surface detail leave the execution uneven.

Callstack Apex

The cheerful yellow bird, cream eyes, orange features and miniature teal console closely match the brief. Clean block edges, restrained colors and soft shadows create an appealing composition. The body reads more like a gridded disc than a fully cubic sphere, and the outlined left wing has limited volume. The right wing reaches the cyan block, though its grip is ambiguous.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
Task & likeness5.0/108.5/10
Anatomy & construction4.5/107.0/10
Space & placement6.0/107.5/10
Light & reflections5.0/107.5/10
Purposeful detail6.0/107.5/10
Artistry & character5.0/107.0/10
Materials & effects5.0/107.0/10
Visual integrity6.5/107.5/10

Benchmark task

Muse Spark Open

A small elephant protecting a delicate seed tests expressive anatomy, physical contact and contrasting organic materials.

Callstack Apex

A rounded bird built from small cubes explores a miniature machine. The scene tests block construction, expressive proportions, contact and soft lighting.

Mona Lisa

Same task instructions

Precise visual recall and portrait reconstruction.

The judgment

Muse Spark Open

A recognizable, orderly interpretation with clean major contours, connected body forms and modest facial shading. Wide eyes, frontal symmetry and schematic hands limit likeness and expression. Layered scenery establishes basic depth, but shallow arm overlaps, flat clothing and sparse fine detail keep the execution basic and uneven.

Callstack Apex

The framed portrait recalls Mona Lisa through dark hair, folded arms and a hazy landscape. Replication is limited by wide, staring eyes, an elongated neck and a downturned mouth. The overlapping hands lack convincing finger and wrist construction. Soft tonal shading suggests volume, but pervasive blur obscures clothing, landscape and anatomical detail.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
Task & likeness3.0/103.5/10
Anatomy & construction3.0/104.0/10
Space & placement5.0/104.5/10
Light & reflections4.5/106.0/10
Purposeful detail4.0/104.5/10
Artistry & character3.0/104.5/10
Materials & effects4.0/105.5/10
Visual integrity6.0/105.5/10

Benchmark task

An SVG interpretation of the Mona Lisa tests facial likeness, anatomy and the composition of a familiar portrait.

Beach

Same task instructions

Creativity, perspective and visual beauty.

The judgment

Muse Spark Open

A coherent sunset beach with readable activities, balanced framing and controlled colour transitions. Small accessories add interest, but schematic anatomy, limited surface detail, weak directional shadows and a geometric reflection constrain its finish. Most shapes and overlaps remain clean.

Callstack Apex

A cohesive sunset beach illustration with lively wildlife, playful accents, and an appealing warm-to-purple palette. Palm framing and the aligned sun reflection organize the scene, while connected silhouettes keep the activities readable. Schematic joints, ambiguous dolphin junctions, loosely matched reflections, and repetitive surface marks limit construction, lighting coherence, and material depth.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
Task & likeness8.0/108.5/10
Anatomy & construction6.0/104.5/10
Space & placement6.5/107.5/10
Light & reflections5.5/105.5/10
Purposeful detail6.5/107.5/10
Artistry & character5.5/106.5/10
Materials & effects6.0/107.0/10
Visual integrity8.0/104.0/10

Benchmark task

A busy shoreline at sunset tests scene composition, animal forms and the relationship between light and water reflections.

Ground Truth

Same task instructions

Physical reasoning, light and visual reconstruction.

The judgment

Muse Spark Open

This benchmark has not been assessed yet.

Callstack Apex

This benchmark has not been assessed yet.

Benchmark task

A plank, computer mouse and blueberry in a steel room test physical stability, spatial relationships, materials and lighting.

Raccoon

Multiple instruction versions

Scene composition and interacting subjects.

The judgment

Muse Spark Open

Expressive faces, distinct accessories and clean color separation make the scene appealing and recognizable. Character detail is stronger than the functional construction: steering contact, limb overlaps and seating remain ambiguous. The readable hull and lively spray establish motion, while limited directional shading and simplified surfaces constrain depth and physical coherence.

Callstack Apex

The raccoon clearly rides the dog's back, and the dog's paws reach the jet ski controls. Expressive faces, a sweeping tail and a strong sunset composition give the illustration character. Limbs remain connected, but the dog's foreleg joints and vehicle seating are loosely constructed. Angular splashes convey speed more successfully than convincing water displacement; lighting and reflections remain decorative.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
Task & likeness4.0/109.0/10
Anatomy & construction3.0/107.0/10
Space & placement6.0/107.5/10
Light & reflections4.5/107.0/10
Purposeful detail7.0/108.5/10
Artistry & character3.5/107.5/10
Materials & effects5.0/107.0/10
Visual integrity5.0/108.0/10

Benchmark task

A jet-ski scene pairs a canine driver with a raccoon passenger. It tests the placement and contact of interacting subjects, along with vehicle construction.

Pelican

Same task instructions

Subject construction and spatial relationships.

The judgment

Muse Spark Open

A controlled, appealing cartoon with a recognizable pelican, expressive face and clean curved forms. Feather lines, spokes and bill shading provide useful complexity. Aligned wheels and a ground shadow establish placement, but uncertain pedal contacts and obscured mechanical connections weaken support and riding action. Lighting remains loosely coordinated with the sun.

Callstack Apex

An appealing cartoon with a distinctive pelican, expressive eye, warm bill and carefully drawn bicycle wheels. The wing reaches the handlebar, but the feet do not clearly engage the pedals, weakening the riding mechanics. Layered hills create depth; limited ground shadows weaken contact. Clean curves and purposeful feather details give the illustration polish.

Score breakdown

CategoryMuse Spark OpenCallstack Apex
Task & likeness7.5/108.5/10
Anatomy & construction5.0/106.5/10
Space & placement6.0/107.5/10
Light & reflections5.0/107.5/10
Purposeful detail6.5/108.0/10
Artistry & character5.5/108.0/10
Materials & effects6.0/107.5/10
Visual integrity7.5/108.0/10

Benchmark task

A cycling pelican tests anatomy, riding posture and contact between the bird and the bicycle.