STEALTHMARK · HEAD TO HEAD

All comparisons ↗

Claude Sonnet 5.5 vs GPT-6.1 Terra

Claude Sonnet 5.5 leads GPT-6.1 Terra by 9.8 points on StealthMark, 70.2 to 60.4. It leads on 7 of 9 benchmarks, including Latch, and GPT-6.1 Terra on 2, including Foresight. Claude Sonnet 5.5 scores higher on Ground Truth.

See the difference ↘
All results ↗
All results ↗

Overall StealthMark

70.2/100Overall rank 3/54
60.4/100Overall rank 9/54

General Intelligence

67.0/100
58.0/100

Visual Intelligence

76.1/100
64.9/100

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
  • GPT-6.1 Terra
  • Other models
  • Median

DATASHEET

Specs and pricing

Claude Sonnet 5.5 scores higher on StealthMark. GPT-6.1 Terra is 2× cheaper per output token. Both take about 1M tokens of context.

  • Claude Sonnet 5.5
  • GPT-6.1 Terra
  • Other models
  • Median
PricePer 1M output tokens, input below
Claude Sonnet 5.5: $10$2 inputGPT-6.1 Terra: $52× cheaper$1 input
Context windowTokens per request, max output below
Claude Sonnet 5.5: 1MTied128K max outputGPT-6.1 Terra: 1.05MTied128K max output
Output speedTokens per second, our measurement
Claude Sonnet 5.5: 249tokens/sGPT-6.1 Terra: Not measured
Developer
AnthropicOpenAI
Released
28 Sep 202626 Oct 2026
Origin
United StatesBoth
Input → output
Text, image → textBoth

Full datasheets, every price and sourceClaude Sonnet 5.5 ↗GPT-6.1 Terra ↗

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 12/50

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

GPT-6.1 Terra 62.0/100Rank 9/50

Survived 2 of 3
Foresight: complete playing field
Level 315 ptsTurn 20 / 20

Points per level

LevelClaude Sonnet 5.5GPT-6.1 Terra
Level 1Second Thoughts
25 ptsSurvived
21 ptsSurvived
Level 2Pressure Pot
10 ptsOut of lives
9 ptsOut of lives
Level 3Hide or Flight
10 ptsSurvived
15 ptsSurvived

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 4/51

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

GPT-6.1 Terra 77.7/100Rank 12/51

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

Points per level

LevelClaude Sonnet 5.5GPT-6.1 Terra
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
10 ptsClearedFinished early · 1 beacon left
9.8 ptsCleared
Level 3Relay vault
19.2 ptsCleared
19.2 ptsCleared
Level 4Passing bay
18.2 ptsClearedFinished early · 3 beacons left
17.8 ptsClearedFinished early · 3 beacons left
Level 5Second thoughts
20.6 ptsCleared
20.6 ptsCleared

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.

GPT-6.1 Terra

The sphere, airborne black and first reflected silhouettes preserve important geometry within the portrait frame. Paint deformation, contact order and forward transport are supported, with a small crimson endpoint overshoot. Major optical omissions dominate: short finite reflection sequences and smooth bands replace extensive, spatially ordered mirror imagery. Dark gloss and crisp upper emitter shapes provide partial material credit.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
State at 600 ms24.0/2523.0/25
Camera and placement15.0/1511.0/15
Reflections35.0/12033.0/120
Materials and scale10.0/107.5/10
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.

GPT-6.1 Terra

A balanced serpent emblem with six attached outward heads, delicate scales and softly rounded bodies. Its compact silhouette reads clearly, but central routing does not establish every alternating crossing or crisp inward corner. Repetitive texture, limited facial anatomy and weak contact shadows constrain its organic character.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
Task & likeness8.0/107.5/10
Anatomy & construction8.0/106.5/10
Space & placement8.0/106.5/10
Light & reflections7.5/106.0/10
Purposeful detail8.0/106.5/10
Artistry & character8.0/106.5/10
Materials & effects8.0/106.0/10
Visual integrity8.5/106.0/10

Benchmark task

Claude Sonnet 5.5

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

GPT-6.1 Terra

A pale serpent woven into an interlocking knot tests connected anatomy, repeated structure and readable overlaps. Organic surface detail must work with the overall geometry.

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.

GPT-6.1 Terra

A recognizable interpretation with developed facial shading, shaped sleeve folds and purposeful small features. These strengths support modest upward calibration, while the frontal torso, elongated proportions, schematic finger joints and unresolved seated support keep replication and construction uneven.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
Task & likeness6.5/105.5/10
Anatomy & construction5.0/106.5/10
Space & placement6.0/104.5/10
Light & reflections6.5/106.5/10
Purposeful detail6.0/106.0/10
Artistry & character6.5/106.0/10
Materials & effects6.0/106.0/10
Visual integrity6.5/106.5/10

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.

GPT-6.1 Terra

A coherent sunset illustration with clear prompt fulfillment, controlled framing and varied, purposeful small details. Simplified joints, frontal staging, flattened animal forms and weakly directional shadows limit its anatomical, spatial and physical sophistication.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
Task & likeness9.0/108.5/10
Anatomy & construction8.0/107.5/10
Space & placement8.5/106.5/10
Light & reflections8.5/105.5/10
Purposeful detail9.5/107.5/10
Artistry & character9.5/107.0/10
Materials & effects8.5/106.5/10
Visual integrity8.0/107.5/10

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.

GPT-6.1 Terra

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.

GPT-6.1 Terra

A coherent cartoon with expressive animals, readable steering and a clear wake. Fine facial and hull details reward inspection. The main limits are the boatlike craft, simplified joints, weakly braced frontal raccoon and minimal directional lighting or material depth.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
Task & likeness8.5/106.5/10
Anatomy & construction7.0/105.5/10
Space & placement8.0/106.0/10
Light & reflections6.5/105.0/10
Purposeful detail8.0/107.0/10
Artistry & character7.0/106.0/10
Materials & effects7.5/106.0/10
Visual integrity8.0/107.0/10

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.

GPT-6.1 Terra

A coherent pelican cyclist with expressive proportions, purposeful feather detail and developed bicycle machinery. Continuous body contours, aligned wheels and readable pedal contacts support the scene. Simplified articulation, shallow modelling and an unresolved steering connection limit construction and placement.

Score breakdown

CategoryClaude Sonnet 5.5GPT-6.1 Terra
Task & likeness9.0/107.0/10
Anatomy & construction7.5/107.0/10
Space & placement7.5/106.0/10
Light & reflections6.5/105.5/10
Purposeful detail8.0/107.0/10
Artistry & character7.5/106.5/10
Materials & effects6.5/105.5/10
Visual integrity8.0/106.0/10

Benchmark task

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