STEALTHMARK · HEAD TO HEAD

All comparisons ↗

GPT-6.1 Terra Low vs Callstack Apex

Callstack Apex leads GPT-6.1 Terra Low by 8.2 points on StealthMark, 49.5 to 41.3. It leads on 5 of the 8 benchmarks with results for both and GPT-6.1 Terra Low on 3, including Latch. Pixel Canary scores higher on Ground Truth.

See the difference ↘
All results ↗
Model guide ↗

Overall StealthMark

41.3/100Overall rank 35/55
49.5/100Overall rank 19/55

General Intelligence

34.3/100
40.4/100

Visual Intelligence

53.1/100
59.6/100

BENCHMARK BY BENCHMARK

Where each model leads

  • GPT-6.1 Terra Low
  • Callstack Apex
  • Other models
  • Median

DATASHEET

Specs and pricing

  • GPT-6.1 Terra Low
  • Callstack Apex
  • Other models
  • Median
PricePer 1M output tokens, input below
GPT-6.1 Terra Low: No list priceCallstack Apex: $3$0.50 input
Context windowTokens per request, max output below
GPT-6.1 Terra Low: Not publishedCallstack Apex: 256K
Output speedTokens per second, our measurement
GPT-6.1 Terra Low: Not measuredCallstack Apex: 255tokens/s
Developer
Not publishedCallstack
Released
Not published1 Oct 2026
Origin
Not publishedPoland
Input → output
Not publishedText → text
Architecture
Not publishedQwen foundation with Callstack domain post-training for React and React Native

Full datasheets, every price and sourceCallstack Apex ↗

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-6.1 Terra Low 36.1/100Rank 26/51

Survived 1 of 3
Foresight: complete playing field
Level 39 ptsTurn 20 / 20

Points per level

LevelGPT-6.1 Terra LowCallstack Apex
Level 1Second Thoughts
4 ptsOut of lives
No run
Level 2Pressure Pot
8 ptsOut of lives
No run
Level 3Hide or Flight
9 ptsSurvived
No run

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-6.1 Terra Low 62.4/100Rank 23/52

Cleared 4 of 5
Latch: complete playing field
Level 520.6 ptsTurn 27 / 40

Callstack Apex 100.0/100Rank 44/521 of 5 levels

1 of 5 played
Latch: complete playing field
Level 15.2 ptsTurn 6 / 12

Points per level

LevelGPT-6.1 Terra LowCallstack Apex
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
9.2 ptsCleared
Pending
Level 3Relay vault
18.8 ptsCleared
Pending
Level 4Passing bay
10.2 ptsFinished early
Not played
Level 5Second thoughts
20.6 ptsCleared
Not played

Newton's Mirror

Same task instructions

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

The judgment

GPT-6.1 Terra Low

Deformed colored paint and a separate airborne black body establish readable interaction history. Cyan has travelled too far, framing differs substantially, and the mirror system supplies only elementary bands and oval copies. Missing recursive geometry, nested spherical imagery and emitter mapping remain the dominant weaknesses.

Callstack Apex

The principal sphere placement and paint contact sequence are supported. Isolated sphere and panel images provide limited optical structure, but missing lateral chains and side-floor continuations prevent a coherent repeating mirror room. The main and reflected spheres lack ordered curved nested imagery, while sparse planar emitter images and incomplete spherical emitter mapping leave most of the reflection system unsupported.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
State at 600 ms22.0/2520.0/25
Camera and placement4.0/1513.0/15
Reflections10.0/12010.0/120
Materials and scale6.0/107.0/10
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

GPT-6.1 Terra Low

Six attached outward-facing heads, delicate scales and soft ivory shading establish an orderly decorative motif. Separate paddle-shaped bodies replace the required interlocking loops and leave no enclosed central hexagon. Surface detail provides interest, but repeated simple forms, schematic faces and limited anatomical modeling constrain the result.

Callstack Apex

The cheerful yellow bird, cream eyes, orange features and miniature teal console closely match the brief. Clean block edges, restrained colors and soft shadows create an appealing composition. The body reads more like a gridded disc than a fully cubic sphere, and the outlined left wing has limited volume. The right wing reaches the cyan block, though its grip is ambiguous.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
Task & likeness4.0/108.5/10
Anatomy & construction3.5/107.0/10
Space & placement4.5/107.5/10
Light & reflections5.5/107.5/10
Purposeful detail5.5/107.5/10
Artistry & character5.0/107.0/10
Materials & effects5.5/107.0/10
Visual integrity4.0/107.5/10

Benchmark task

GPT-6.1 Terra Low

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.

Callstack Apex

A rounded bird built from small cubes explores a miniature machine. The scene tests block construction, expressive proportions, contact and soft lighting.

Mona Lisa

Different task instructions

Precise visual recall and portrait reconstruction.

The judgment

GPT-6.1 Terra Low

A recognizable, coherent portrait with purposeful facial detail, warm local volume and layered scenery. The frontal pose, enlarged face, merged hands and shallow clothing construction substantially limit replication and drawing skill. The visible successes support retaining the current assessment.

Callstack Apex

The framed portrait recalls Mona Lisa through dark hair, folded arms and a hazy landscape. Replication is limited by wide, staring eyes, an elongated neck and a downturned mouth. The overlapping hands lack convincing finger and wrist construction. Soft tonal shading suggests volume, but pervasive blur obscures clothing, landscape and anatomical detail.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
Task & likeness5.0/103.5/10
Anatomy & construction4.5/104.0/10
Space & placement5.0/104.5/10
Light & reflections6.0/106.0/10
Purposeful detail5.0/104.5/10
Artistry & character5.5/104.5/10
Materials & effects5.0/105.5/10
Visual integrity6.0/105.5/10

Benchmark task

An SVG interpretation of the Mona Lisa tests facial likeness, anatomy and the composition of a familiar portrait.

Beach

Different task instructions

Creativity, perspective and visual beauty.

The judgment

GPT-6.1 Terra Low

A coherent sunset scene demonstrates the beach, animals, birds and reflections. Flowing silhouettes, warm color transitions and intact attachments are its strongest properties. Simplified anatomy, the turtle's elevated viewing angle and symbolic surface effects constrain drawing complexity and physical depth.

Callstack Apex

A cohesive sunset beach illustration with lively wildlife, playful accents, and an appealing warm-to-purple palette. Palm framing and the aligned sun reflection organize the scene, while connected silhouettes keep the activities readable. Schematic joints, ambiguous dolphin junctions, loosely matched reflections, and repetitive surface marks limit construction, lighting coherence, and material depth.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
Task & likeness8.0/108.5/10
Anatomy & construction5.5/104.5/10
Space & placement5.5/107.5/10
Light & reflections6.5/105.5/10
Purposeful detail6.0/107.5/10
Artistry & character5.0/106.5/10
Materials & effects5.5/107.0/10
Visual integrity7.5/104.0/10

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

GPT-6.1 Terra Low

This benchmark has not been assessed yet.

Callstack Apex

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

Multiple instruction versions

Scene composition and interacting subjects.

The judgment

GPT-6.1 Terra Low

Recognizable animals, a coherent craft and sweeping wake make an appealing cartoon. Basic limb construction, weakly demonstrated raccoon seating and limited shared perspective constrain the scene. Small identifying details work well, while lighting and materials remain broadly graphic.

Callstack Apex

The raccoon clearly rides the dog's back, and the dog's paws reach the jet ski controls. Expressive faces, a sweeping tail and a strong sunset composition give the illustration character. Limbs remain connected, but the dog's foreleg joints and vehicle seating are loosely constructed. Angular splashes convey speed more successfully than convincing water displacement; lighting and reflections remain decorative.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
Task & likeness6.5/109.0/10
Anatomy & construction5.0/107.0/10
Space & placement5.5/107.5/10
Light & reflections4.5/107.0/10
Purposeful detail6.0/108.5/10
Artistry & character5.0/107.5/10
Materials & effects5.0/107.0/10
Visual integrity6.0/108.0/10

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 instructions

Subject construction and spatial relationships.

The judgment

GPT-6.1 Terra Low

A coherent coastal illustration with a distinctive pelican, controlled contours and clearly organised bicycle wheels. Visible saddle support and shaped neck and wing contours earn credit beyond basic geometric construction. Rubbery legs, unresolved pedal contacts and absent steering contact limit the riding action. Lighting and materials remain restrained and spatially shallow.

Callstack Apex

An appealing cartoon with a distinctive pelican, expressive eye, warm bill and carefully drawn bicycle wheels. The wing reaches the handlebar, but the feet do not clearly engage the pedals, weakening the riding mechanics. Layered hills create depth; limited ground shadows weaken contact. Clean curves and purposeful feather details give the illustration polish.

Score breakdown

CategoryGPT-6.1 Terra LowCallstack Apex
Task & likeness7.0/108.5/10
Anatomy & construction5.5/106.5/10
Space & placement6.0/107.5/10
Light & reflections5.5/107.5/10
Purposeful detail6.5/108.0/10
Artistry & character6.0/108.0/10
Materials & effects6.0/107.5/10
Visual integrity6.0/108.0/10

Benchmark task

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