STEALTHMARK · HEAD TO HEAD

All comparisons ↗

Claude Fable 5.1 vs GPT-6.1 Terra

Claude Fable 5.1 leads GPT-6.1 Terra by 2.6 points on StealthMark, 63.0 to 60.4. It leads on 7 of 9 benchmarks, including Latch, and GPT-6.1 Terra on 2, including Foresight. Claude Fable 5.1 scores higher on Newton's Mirror, with its largest category advantage in reflections.

See the difference ↘
All results ↗
All results ↗

Overall StealthMark

63.0/100Overall rank 7/54
60.4/100Overall rank 9/54

General Intelligence

60.6/100
58.0/100

Visual Intelligence

67.1/100
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

BENCHMARK BY BENCHMARK

Where each model leads

  • Claude Fable 5.1
  • GPT-6.1 Terra
  • Other models
  • Median

DATASHEET

Specs and pricing

Claude Fable 5.1 scores higher on StealthMark. GPT-6.1 Terra is 10× cheaper per output token. Both take about 1M tokens of context.

  • Claude Fable 5.1
  • GPT-6.1 Terra
  • Other models
  • Median
PricePer 1M output tokens, input below
Claude Fable 5.1: $50$10 inputGPT-6.1 Terra: $510× cheaper$1 input
Context windowTokens per request, max output below
Claude Fable 5.1: 1MTied128K max outputGPT-6.1 Terra: 1.05MTied128K max output
Output speedTokens per second, our measurement
Claude Fable 5.1: 122tokens/sGPT-6.1 Terra: Not measured
Developer
AnthropicOpenAI
Released
1 Sep 202626 Oct 2026
Origin
United StatesBoth
Input → output
Text, image → textBoth

Full datasheets, every price and sourceClaude Fable 5.1 ↗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 Fable 5.1 34.2/100Rank 39/502 of 3 levels

2 of 3 played
Foresight: complete playing field
Level 38 ptsTurn 17 / 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 Fable 5.1GPT-6.1 Terra
Level 1Second Thoughts
21 ptsOut of lives
21 ptsSurvived
Level 2Pressure Pot
Pending
9 ptsOut of lives
Level 3Hide or Flight
8 ptsOut of lives
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 Fable 5.1 82.6/100Rank 6/51

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 Fable 5.1GPT-6.1 Terra
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
9.8 ptsCleared
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 Fable 5.1

The broad paint sequence, bilateral near-field sphere arrangement, overlaps and diminishing panel repetitions are recognizable; crimson is slightly too low. Small paint scale and basic shading provide material cues, although the steel response remains soft. Inaccurate light projections, missing outer chains and incomplete nested room imagery remain the principal limitations.

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 Fable 5.1GPT-6.1 Terra
State at 600 ms24.0/2523.0/25
Camera and placement14.0/1511.0/15
Reflections48.0/12033.0/120
Materials and scale7.5/107.5/10
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 Fable 5.1

The coral palette, friendly face, matte shading and cream arch create a coherent emblem. However, the mantle is elongated rather than compact, and the appendages spread mostly sideways and downward instead of forming an evenly spaced, flower-like starburst. Two thin hanging appendages weaken the thick-arm motif. Clean contours and balanced framing support the simple design.

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 Fable 5.1GPT-6.1 Terra
Task & likeness6.5/107.5/10
Anatomy & construction7.0/106.5/10
Space & placement7.5/106.5/10
Light & reflections6.5/106.0/10
Purposeful detail6.0/106.5/10
Artistry & character7.0/106.5/10
Materials & effects6.5/106.0/10
Visual integrity8.0/106.0/10

Benchmark task

Claude Fable 5.1

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

Same task instructions

Precise visual recall and portrait reconstruction.

The judgment

Claude Fable 5.1

The dark clothing, crossed hands and hazy landscape establish the Mona Lisa composition. Replication is limited by the frontal, elongated face, wide eyes and simplified smile. Rounded, parallel fingers and unclear wrist transitions weaken the hands. Warm facial shading gives some volume, but broad garment shapes and scattered crack marks substitute for convincing folds and painterly detail.

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 Fable 5.1GPT-6.1 Terra
Task & likeness5.5/105.5/10
Anatomy & construction6.0/106.5/10
Space & placement6.0/104.5/10
Light & reflections6.0/106.5/10
Purposeful detail5.0/106.0/10
Artistry & character5.5/106.0/10
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 Fable 5.1

The colorful sunset, layered shoreline, animals, kite and beach toys fulfill the lively beach brief. Clean silhouettes and a balanced composition give the illustration character. Construction is simplified: the umbrella resembles a segmented fan, dolphins have weak water interaction, and the sun’s reflection forms a rigid widening wedge. Flat surfaces and sparse contact shadows limit depth.

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 Fable 5.1GPT-6.1 Terra
Task & likeness8.5/108.5/10
Anatomy & construction7.0/107.5/10
Space & placement7.0/106.5/10
Light & reflections7.0/105.5/10
Purposeful detail7.5/107.5/10
Artistry & character7.5/107.0/10
Materials & effects6.5/106.5/10
Visual integrity7.5/107.5/10

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 Fable 5.1

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 Fable 5.1

The raccoon rides on the dog's back, and the dog's extended foreleg reaches the jet ski controls. Expressive faces, a clear silhouette and sweeping spray make the action readable. Limb and handlebar overlaps weaken construction; broad shading provides limited volume, and the glowing sun has little corresponding reflection on the water. Clean vector shapes support an appealing but simplified illustration.

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 Fable 5.1GPT-6.1 Terra
Task & likeness8.5/106.5/10
Anatomy & construction6.5/105.5/10
Space & placement7.0/106.0/10
Light & reflections5.5/105.0/10
Purposeful detail7.0/107.0/10
Artistry & character7.0/106.0/10
Materials & effects6.5/106.0/10
Visual integrity7.5/107.0/10

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 Fable 5.1

The pelican reads clearly, with an expressive face, prominent bill and appealing composition. Both legs connect to the body, but the far foot's pedal contact and the wing's steering grip remain unclear. Wheel alignment and background layers are coherent. Clean contours and feather lines give polish, while schematic machinery, limited surface texture and weak directional lighting constrain the finish.

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 Fable 5.1GPT-6.1 Terra
Task & likeness8.5/107.0/10
Anatomy & construction7.0/107.0/10
Space & placement7.5/106.0/10
Light & reflections6.0/105.5/10
Purposeful detail7.0/107.0/10
Artistry & character7.0/106.5/10
Materials & effects6.0/105.5/10
Visual integrity8.0/106.0/10

Benchmark task

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