STEALTHMARK · HEAD TO HEAD
All comparisons ↗Fledge Alpha vs Step 5 Preview
Step 5 Preview leads Fledge Alpha by 3.2 points on StealthMark, 39.0 to 35.8. Fledge Alpha leads on 5 of the 7 benchmarks with results for both and Step 5 Preview on 2. Step 5 Preview scores higher on Newton's Mirror, with its largest category advantage in reflections.
See the difference ↘Overall StealthMark
General Intelligence
Visual Intelligence
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
- Fledge AlphaMulti-step reasoning not measured
BENCHMARK BY BENCHMARK
Where each model leads
- Fledge Alpha
- Step 5 Preview
- Other models
- Median
Games
SVG
DATASHEET
Specs and pricing
- Fledge Alpha
- Step 5 Preview
- Other models
- Median
- Developer
- Not publishedStepFun
- Input → output
- Not publishedText, image, video → text
- Architecture
- Not publishedSparse mixture-of-experts; 92 layers (88 MoE), 352 routed experts with 8 selected per token plus a shared expert; grouped-query attention with 512-token sliding windows and full attention every fourth layer; 3 multi-token-prediction layers; vision tower for image and video input
Full datasheets, every price and sourceStep 5 Preview ↗
Foresight
Play Foresight yourselfAnticipating 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.
Step 5 Preview 59.9/100Rank 42/491 of 3 levels

Points per level
Latch
Play Latch yourselfCooperative 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.
Fledge AlphaNo run
Step 5 Preview 40.7/100Rank 28/50

Points per level
Newton's Mirror
Same task instructionsPhysics, perspective and recursive reflections, tested together. Explore the test ↗
Fledge Alpha 16.4/100 Rank 41/53

Step 5 Preview 37.9/100 Rank 19/53

The judgment
Fledge Alpha
The candidate communicates a round metallic sphere, three paint colors and a separate airborne black blob. Its hovering support relationship, displaced framing and unresolved paint interaction limit physical credit. Sparse planar light ghosts and a soft sphere highlight provide little evidence for the required wall/floor repetitions and curved nested mirror imagery.
Step 5 Preview
The main sphere, airborne black and small colored features occupy broadly appropriate positions. Most of the defining mirror system is absent, and paint interaction remains only partially supported. The small paint features do not visibly establish a separate volume-scale violation.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| State at 600 ms | 9.0/25 | 20.0/25 |
| Camera and placement | 5.0/15 | 13.5/15 |
| Reflections | 7.5/120 | 20.0/120 |
| Materials and scale | 3.5/10 | 7.0/10 |
| Floor-damage reward | 0.0/10 | 0.0/10 |
Benchmark task
A spinning metal sphere and paint in a mirrored room test physical reasoning, perspective and consistency across repeated reflections.
Selfie
Different task instructionsVisual construction and creative interpretation.
Fledge Alpha 61.1/100 Rank 30/53

Step 5 Preview 52.0/100 Rank 40/53

The judgment
Fledge Alpha
A coherent, appealing mascot with expressive eyes, a cheerful beak and a readable swept-back silhouette. Its larger forward foot and trailing feathers suggest a running stride, but the upright body, stiff legs and minimally articulated feet limit convincing motion. Clean flat shapes suit the brief, while uneven feather junctions and incomplete cream accents reduce polish.
Step 5 Preview
A charming diagonal climber and warm palette communicate the central idea. Simple rounded construction, crowded limb counting, uncertain footholds and an unattached upper shelf limit its physical coherence. Growth bands and the yarn trail add specificity, but the requested material distinctions and unravelled bootie remain underdeveloped.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| Task & likeness | 7.5/10 | 6.0/10 |
| Anatomy & construction | 6.5/10 | 4.5/10 |
| Space & placement | 7.0/10 | 5.0/10 |
| Light & reflections | 5.5/10 | 5.5/10 |
| Purposeful detail | 6.5/10 | 5.5/10 |
| Artistry & character | 4.0/10 | 5.0/10 |
| Materials & effects | 6.0/10 | 6.0/10 |
| Visual integrity | 6.5/10 | 5.0/10 |
Benchmark task
Fledge Alpha
An eager young seabird running toward the viewer tests expressive anatomy, balance and a convincing forward-moving pose.
Step 5 Preview
Character scenes test expression, anatomy, materials and coherent visual construction.
Mona Lisa
Different task instructionsPrecise visual recall and portrait reconstruction.
Fledge Alpha 28.3/100 Rank 35/53

Step 5 Preview 38.4/100 Rank 27/53

The judgment
Fledge Alpha
A recognizable but basic Mona Lisa reinterpretation with a coherent silhouette and subdued palette. Curtain-like hair obscures much of the face, while elongated facial construction and oversized, minimally articulated hands substantially weaken replication. Soft shading supplies modest volume, but anatomy, landscape depth and purposeful detail remain underdeveloped.
Step 5 Preview
A recognizable, coherent simplification with purposeful facial contours and differentiated fingers. These provide more construction and detail than the broad silhouette alone suggests. The oversized face, frontal seated pose, unresolved wrists and sparse landscape still substantially limit likeness, depth and finish.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| Task & likeness | 3.0/10 | 4.0/10 |
| Anatomy & construction | 3.0/10 | 4.0/10 |
| Space & placement | 2.5/10 | 4.0/10 |
| Light & reflections | 2.5/10 | 3.5/10 |
| Purposeful detail | 3.0/10 | 4.0/10 |
| Artistry & character | 3.0/10 | 4.0/10 |
| Materials & effects | 2.5/10 | 3.0/10 |
| Visual integrity | 2.5/10 | 3.5/10 |
Benchmark task
An SVG interpretation of the Mona Lisa tests facial likeness, anatomy and the composition of a familiar portrait.
Beach
Different task instructionsCreativity, perspective and visual beauty.
Fledge Alpha 43.4/100 Rank 45/53

Step 5 Preview 33.5/100 Rank 48/53

The judgment
Fledge Alpha
A cheerful, recognizable sunset beach with a cohesive warm palette and clear accessories. Simple construction, uncertain palm support, an ambiguous upper boundary and schematic reflections limit depth and finish. The scene communicates its subject successfully but lacks the developed forms, lighting and detail of exceptional illustration.
Step 5 Preview
A recognizable sunset beach with clear warm-cool contrast and playful accessories. Basic animal construction, shallow foreground placement and schematic reflections limit spatial and physical credibility. Sparse descriptive detail and abruptly ended sky bands constrain the finish.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| Task & likeness | 7.5/10 | 4.0/10 |
| Anatomy & construction | 4.0/10 | 3.0/10 |
| Space & placement | 5.5/10 | 3.5/10 |
| Light & reflections | 5.0/10 | 3.5/10 |
| Purposeful detail | 3.0/10 | 3.0/10 |
| Artistry & character | 3.0/10 | 3.0/10 |
| Materials & effects | 2.5/10 | 3.5/10 |
| Visual integrity | 4.0/10 | 4.0/10 |
Benchmark task
A busy shoreline at sunset tests scene composition, animal forms and the relationship between light and water reflections.
Ground Truth
Same task instructionsPhysical reasoning, light and visual reconstruction.
Fledge Alpha 36.8/100 Rank 32/53

Step 5 Preview 33.3/100 Rank 35/53

The judgment
Fledge Alpha
This benchmark has not been assessed yet.
Step 5 Preview
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
Same task instructionsScene composition and interacting subjects.
Fledge Alpha 63.4/100 Rank 20/53

Step 5 Preview 37.8/100 Rank 44/53

The judgment
Fledge Alpha
An appealing sunset illustration with recognizable characters and a clear riding action. Color, expression and silhouette are stronger than anatomical construction: overlapping paws obscure support, the dog's steering limb is simplified, and the vehicle controls lack definition. The wake conveys movement, while lighting and water reflections remain decorative.
Step 5 Preview
Recognizable animals, a bright palette and identifying accessories support a basic cartoon. Primitive anatomy, partial seated support, unresolved steering and weak hull-water contact limit the central action. Lighting and spray provide atmosphere without establishing convincing physical depth.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| Task & likeness | 8.5/10 | 4.0/10 |
| Anatomy & construction | 5.5/10 | 4.5/10 |
| Space & placement | 7.5/10 | 3.0/10 |
| Light & reflections | 6.5/10 | 3.5/10 |
| Purposeful detail | 7.0/10 | 4.0/10 |
| Artistry & character | 5.5/10 | 3.5/10 |
| Materials & effects | 7.0/10 | 3.0/10 |
| Visual integrity | 4.5/10 | 3.0/10 |
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
Different task instructionsSubject construction and spatial relationships.
Fledge Alpha 60.5/100 Rank 34/53

Step 5 Preview 30.0/100 Rank 51/53

The judgment
Fledge Alpha
A clear, cheerful illustration with a recognizable pelican, coherent bicycle silhouette and tidy composition. Simplified leg articulation, steering contact, mechanical detail and lighting keep it at a competent illustrative level.
Step 5 Preview
The pelican and bicycle are recognizable, with a pleasant palette and basic diffuse shading. The riding relationship fails physically: the bird is unsupported, the front wheel is unmounted, and pedalling is unresolved. Simple geometric construction and sparse material treatment further limit the drawing.
Score breakdown
| Category | Fledge Alpha | Step 5 Preview |
|---|---|---|
| Task & likeness | 8.0/10 | 3.0/10 |
| Anatomy & construction | 6.0/10 | 3.0/10 |
| Space & placement | 6.5/10 | 3.0/10 |
| Light & reflections | 4.5/10 | 3.0/10 |
| Purposeful detail | 5.5/10 | 4.0/10 |
| Artistry & character | 5.0/10 | 3.0/10 |
| Materials & effects | 5.5/10 | 3.0/10 |
| Visual integrity | 6.5/10 | 2.0/10 |
Benchmark task
A cycling pelican tests anatomy, riding posture and contact between the bird and the bicycle.