STEALTHMARK · HEAD TO HEAD

All comparisons ↗

Claude Sonnet 5.5 vs Step 5 Preview

Claude Sonnet 5.5 leads Step 5 Preview by 31.2 points on StealthMark, 70.2 to 39.0. It leads on all 9 benchmarks. Claude Sonnet 5.5 scores higher on Beach, with its largest category advantage in anatomy & construction.

See the difference ↘
All results ↗
All results ↗

Overall StealthMark

70.2/100Overall rank 3/53
39.0/100Overall rank 36/53

General Intelligence

67.0/100
37.1/100

Visual Intelligence

76.1/100
41.9/100

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

  • Claude Sonnet 5.5

BENCHMARK BY BENCHMARK

Where each model leads

  • Claude Sonnet 5.5
  • Step 5 Preview
  • Other models
  • Median

DATASHEET

Specs and pricing

Both take about 1M tokens of context.

  • Claude Sonnet 5.5
  • Step 5 Preview
  • Other models
  • Median
PricePer 1M output tokens, input below
Claude Sonnet 5.5: $10$2 inputStep 5 Preview: No list price
Context windowTokens per request, max output below
Claude Sonnet 5.5: 1MTied128K max outputStep 5 Preview: 1MTied
Output speedTokens per second, our measurement
Claude Sonnet 5.5: 249tokens/sStep 5 Preview: Not measured
SizeTotal and active parameters
Claude Sonnet 5.5: Not disclosedStep 5 Preview: 600B27B active
Developer
AnthropicStepFun
Released
28 Sep 2026Not published
Origin
United StatesNot published
Input → output
Text, image → textText, 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 sourceClaude Sonnet 5.5 ↗Step 5 Preview ↗

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.

Claude Sonnet 5.5 59.6/100Rank 11/49

Survived 2 of 3
Foresight: complete playing field
Level 310 ptsTurn 20 / 20

Step 5 Preview 59.9/100Rank 42/491 of 3 levels

1 of 3 played
Foresight: complete playing field
Level 122 ptsTurn 28 / 28

Points per level

LevelClaude Sonnet 5.5Step 5 Preview
Level 1Second Thoughts
25 ptsSurvived
22 ptsSurvived
Level 2Pressure Pot
10 ptsOut of lives
Pending
Level 3Hide or Flight
10 ptsSurvived
Pending

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.

Claude Sonnet 5.5 83.9/100Rank 4/50

Cleared 5 of 5
Latch: complete playing field
Level 520.6 ptsTurn 27 / 40

Step 5 Preview 40.7/100Rank 28/50

Cleared 4 of 5
Latch: complete playing field
Level 515 ptsTurn 35 / 40

Points per level

LevelClaude Sonnet 5.5Step 5 Preview
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
10 ptsClearedFinished early · 1 beacon left
9 ptsCleared
Level 3Relay vault
19.2 ptsCleared
18.6 ptsCleared
Level 4Passing bay
18.2 ptsClearedFinished early · 3 beacons left
15.6 ptsClearedFinished early · 3 beacons left
Level 5Second thoughts
20.6 ptsCleared
15 ptsFinished early

Newton's Mirror

Same task instructions

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

The judgment

Claude Sonnet 5.5

The near-field silhouettes, broad perspective and paint contact order are recognizable. Missing outer chains, truncated repetitions and absent ordered imagery within the main and reflected spheres substantially limit the reflection system. Sparse spherical highlights leave much of the curved room and emitter mapping unsupported, despite some plausible planar light sequences.

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

CategoryClaude Sonnet 5.5Step 5 Preview
State at 600 ms24.0/2520.0/25
Camera and placement15.0/1513.5/15
Reflections35.0/12020.0/120
Materials and scale10.0/107.0/10
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

Claude Sonnet 5.5

The centered coral squid has a friendly, composed expression and a balanced flower-like silhouette. Eight thick arms and two slender tentacles remain visibly connected, with no inverted parts. The mantle is elongated rather than compact, and the arm spacing is uneven. Soft shading gives volume, but dense stippling weakens the requested smooth matte finish; the broad background halo makes depth less precise.

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

CategoryClaude Sonnet 5.5Step 5 Preview
Task & likeness8.0/106.0/10
Anatomy & construction8.0/104.5/10
Space & placement8.0/105.0/10
Light & reflections7.5/105.5/10
Purposeful detail8.0/105.5/10
Artistry & character8.0/105.0/10
Materials & effects8.0/106.0/10
Visual integrity8.5/105.0/10

Benchmark task

Claude Sonnet 5.5

A coral squid with spreading arms tests connected anatomy, balanced composition and soft surface shading.

Step 5 Preview

Character scenes test expression, anatomy, materials and coherent visual construction.

Mona Lisa

Different task instructions

Precise visual recall and portrait reconstruction.

The judgment

Claude Sonnet 5.5

The crossed hands, dark dress, restrained smile and winding landscape clearly recall the Mona Lisa. Replication is limited by the frontal symmetry, wide eyes, elongated neck and flattened fingers. Soft facial shading provides volume, but heavy darkness and pervasive crackle obscure forms. The composition is coherent; the landscape and fabric remain visibly schematic.

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

CategoryClaude Sonnet 5.5Step 5 Preview
Task & likeness6.5/104.0/10
Anatomy & construction5.0/104.0/10
Space & placement6.0/104.0/10
Light & reflections6.5/103.5/10
Purposeful detail6.0/104.0/10
Artistry & character6.5/104.0/10
Materials & effects6.0/103.0/10
Visual integrity6.5/103.5/10

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

Claude Sonnet 5.5

A richly designed beach illustration combines radiant sunset bands, intricate palm fans and playful silhouettes within a cohesive purple, coral and turquoise palette. Carefully varied accessories reward close inspection, while overlapping foreground forms and shoreline layers organize the abundant activity. Dense palm strokes compete with focal subjects; animal anatomy, relative scales and reflected silhouettes remain simplified.

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

CategoryClaude Sonnet 5.5Step 5 Preview
Task & likeness9.0/104.0/10
Anatomy & construction8.0/103.0/10
Space & placement8.5/103.5/10
Light & reflections8.5/103.5/10
Purposeful detail9.5/103.0/10
Artistry & character9.5/103.0/10
Materials & effects8.5/103.5/10
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

Claude Sonnet 5.5

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 instructions

Scene composition and interacting subjects.

The judgment

Claude Sonnet 5.5

The raccoon clearly rides on the dog's back while the dog grips the jet ski controls. Expressive faces, vivid colors and a sweeping wake make the scene appealing. Visible limbs connect coherently, but overlapping steering paws and an indistinct control mounting weaken construction. Flat character lighting and simplified water limit depth and material realism.

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

CategoryClaude Sonnet 5.5Step 5 Preview
Task & likeness8.5/104.0/10
Anatomy & construction7.0/104.5/10
Space & placement8.0/103.0/10
Light & reflections6.5/103.5/10
Purposeful detail8.0/104.0/10
Artistry & character7.0/103.5/10
Materials & effects7.5/103.0/10
Visual integrity8.0/103.0/10

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

Claude Sonnet 5.5

The pelican is immediately recognizable, with an expressive face, generous bill and appealing cycling pose. Spokes, chain, feathers and scarf provide purposeful detail. The bicycle largely holds together, though overlapping angular legs obscure the far foot’s pedal contact. Clean outlines and balanced composition succeed; flat surfaces and limited directional lighting constrain depth.

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

CategoryClaude Sonnet 5.5Step 5 Preview
Task & likeness9.0/103.0/10
Anatomy & construction7.5/103.0/10
Space & placement7.5/103.0/10
Light & reflections6.5/103.0/10
Purposeful detail8.0/104.0/10
Artistry & character7.5/103.0/10
Materials & effects6.5/103.0/10
Visual integrity8.0/102.0/10

Benchmark task

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