STEALTHMARK · HEAD TO HEAD

All comparisons ↗

GPT-5.5 vs GPT-6.1 Terra

GPT-6.1 Terra leads GPT-5.5 by 23.9 points on StealthMark, 60.4 to 36.5. It leads on all 9 benchmarks. GPT-6.1 Terra scores higher on Newton's Mirror, with its largest category advantage in reflections.

See the difference ↘
All results ↗
All results ↗

Overall StealthMark

36.5/100Overall rank 39/54
60.4/100Overall rank 9/54

General Intelligence

36.6/100
58.0/100

Visual Intelligence

36.3/100
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

  • GPT-5.5
  • GPT-6.1 Terra
  • Other models
  • Median

DATASHEET

Specs and pricing

GPT-6.1 Terra scores higher on StealthMark and is 6× cheaper per output token. Both take about 1.05M tokens of context.

  • GPT-5.5
  • GPT-6.1 Terra
  • Other models
  • Median
PricePer 1M output tokens, input below
GPT-5.5: $30$5 inputGPT-6.1 Terra: $56× cheaper$1 input
Context windowTokens per request, max output below
GPT-5.5: 1.05MTied128K max outputGPT-6.1 Terra: 1.05MTied128K max output
Output speedTokens per second, our measurement
GPT-5.5: 193tokens/sGPT-6.1 Terra: Not measured
Developer
OpenAIBoth
Released
23 Apr 202626 Oct 2026
Origin
United StatesBoth
Input → output
Text, image → textBoth

Full datasheets, every price and sourceGPT-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.

GPT-5.5 38.7/100Rank 36/502 of 3 levels

2 of 3 played
Foresight: complete playing field
Level 25 ptsTurn 9 / 18

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

LevelGPT-5.5GPT-6.1 Terra
Level 1Second Thoughts
17 ptsOut of lives
21 ptsSurvived
Level 2Pressure Pot
5 ptsOut of lives
9 ptsOut of lives
Level 3Hide or Flight
Not played
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.

GPT-5.5 71.7/100Rank 17/51

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

LevelGPT-5.5GPT-6.1 Terra
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
9.8 ptsCleared
9.8 ptsCleared
Level 3Relay vault
18.8 ptsCleared
19.2 ptsCleared
Level 4Passing bay
17.2 ptsClearedFinished early · 1 beacon 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

GPT-5.5

The paint ordering and separate black bead support part of the physical state, but adhesion and rotational transport remain only partly established. The sweeping cyan arc and long crimson lobes do not clearly communicate the limited time since their respective impacts. The main sphere is too large and too low, and the black bead is below its required projected position. Displaced isolated sphere images, a flattened floor echo and missing recursive, nested and emitter reflections provide little coherent optical structure. The colored paint is excessively bulky for the specified quantities.

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

CategoryGPT-5.5GPT-6.1 Terra
State at 600 ms15.0/2523.0/25
Camera and placement6.0/1511.0/15
Reflections5.0/12033.0/120
Materials and scale6.0/107.5/10
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

Same task instructions

Visual construction and creative interpretation.

The judgment

GPT-5.5

Six pale, scaled lobes form a balanced radial arrangement, but they remain separate capsules rather than an interlocking serpent knot. There are no crossings, alternating overlaps, or crisp inner bends; the central hexagon is an isolated outline. Small outward-facing heads sit within the lobes without integrated necks. Soft shading and tidy contours provide some finish, while repetitive oval scales and cartoon faces limit organic credibility.

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

CategoryGPT-5.5GPT-6.1 Terra
Task & likeness3.0/107.5/10
Anatomy & construction3.0/106.5/10
Space & placement5.0/106.5/10
Light & reflections5.0/106.0/10
Purposeful detail4.5/106.5/10
Artistry & character4.0/106.5/10
Materials & effects4.5/106.0/10
Visual integrity7.0/106.0/10

Benchmark task

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

GPT-5.5

The veil, restrained smile, crossed hands and muted landscape establish Mona Lisa references. The oversized frontal face and schematic features weaken likeness and expression, while fingerless tapered hand shapes leave anatomy unresolved. Clean contours and balanced framing provide coherence, but sparse garment detail, broad landscape bands and shallow shading limit the portrait's sophistication.

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

CategoryGPT-5.5GPT-6.1 Terra
Task & likeness1.5/105.5/10
Anatomy & construction1.5/106.5/10
Space & placement1.5/104.5/10
Light & reflections2.0/106.5/10
Purposeful detail2.5/106.0/10
Artistry & character1.5/106.0/10
Materials & effects2.0/106.0/10
Visual integrity1.5/106.5/10

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

GPT-5.5

The sunset, palms, birds, playful animals and ball clearly establish the requested beach scene. Warm sky gradients and clean silhouettes make it appealing. Animal construction is underdeveloped: torso and limb connections are unclear, especially in the round-eared foreground figure. The dolphin lacks a convincing splash, and broad reflection bands suggest sunset light without resolving its behavior on water.

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

CategoryGPT-5.5GPT-6.1 Terra
Task & likeness7.0/108.5/10
Anatomy & construction2.5/107.5/10
Space & placement3.0/106.5/10
Light & reflections3.0/105.5/10
Purposeful detail3.0/107.5/10
Artistry & character3.0/107.0/10
Materials & effects3.0/106.5/10
Visual integrity3.5/107.5/10

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

GPT-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

GPT-5.5

The raccoon's masked face, bright hull and sweeping wake make the scene readable and lively. The dog is much less resolved: its head is ambiguous, overlapping brown forms obscure its anatomy, and its paws do not visibly grip the controls. Smooth shapes and cheerful colors provide appeal, but weak steering construction and limited depth keep the drawing uneven.

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

CategoryGPT-5.5GPT-6.1 Terra
Task & likeness3.5/106.5/10
Anatomy & construction3.0/105.5/10
Space & placement4.5/106.0/10
Light & reflections5.0/105.0/10
Purposeful detail3.5/107.0/10
Artistry & character3.0/106.0/10
Materials & effects5.0/106.0/10
Visual integrity3.0/107.0/10

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

GPT-5.5

The oversized bill, bright bicycle and sunset create an appealing, recognizable cartoon. Riding mechanics are less convincing: the wing has no clear steering contact, leg attachments are uneven, and feet do not visibly engage pedals. A dark notch complicates the rear neck junction. Clean contours and orderly spokes provide polish, while simplified anatomy and lighting limit 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

CategoryGPT-5.5GPT-6.1 Terra
Task & likeness7.5/107.0/10
Anatomy & construction4.5/107.0/10
Space & placement6.5/106.0/10
Light & reflections6.5/105.5/10
Purposeful detail5.5/107.0/10
Artistry & character5.0/106.5/10
Materials & effects6.0/105.5/10
Visual integrity7.5/106.0/10

Benchmark task

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