STEALTHMARK · HEAD TO HEAD

All comparisons ↗

GPT-6.1 Terra vs Callstack Apex

GPT-6.1 Terra leads Callstack Apex by 10.9 points on StealthMark, 60.4 to 49.5. It leads on 5 of the 8 benchmarks with results for both, including Latch, and Callstack Apex on 3. GPT-6.1 Terra scores higher on Newton's Mirror, with its largest category advantage in reflections.

See the difference ↘
All results ↗
Model guide ↗

Overall StealthMark

60.4/100Overall rank 9/54
49.5/100Overall rank 19/54

General Intelligence

58.0/100
40.4/100

Visual Intelligence

64.9/100
59.6/100

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-6.1 Terra
  • Callstack Apex
  • Other models
  • Median

DATASHEET

Specs and pricing

GPT-6.1 Terra scores higher on StealthMark and takes 4× more context. Callstack Apex is 1.7× cheaper per output token.

  • GPT-6.1 Terra
  • Callstack Apex
  • Other models
  • Median
PricePer 1M output tokens, input below
GPT-6.1 Terra: $5$1 inputCallstack Apex: $31.7× cheaper$0.50 input
Context windowTokens per request, max output below
GPT-6.1 Terra: 1.05M4× larger128K max outputCallstack Apex: 256K
Output speedTokens per second, our measurement
GPT-6.1 Terra: Not measuredCallstack Apex: 255tokens/s
Developer
OpenAICallstack
Released
26 Oct 20261 Oct 2026
Origin
United StatesPoland
Input → output
Text, image → textText → text
Architecture
Not publishedQwen foundation with Callstack domain post-training for React and React Native

Full datasheets, every price and sourceGPT-6.1 Terra ↗Callstack 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 62.0/100Rank 9/50

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

Points per level

LevelGPT-6.1 TerraCallstack Apex
Level 1Second Thoughts
21 ptsSurvived
No run
Level 2Pressure Pot
9 ptsOut of lives
No run
Level 3Hide or Flight
15 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 77.7/100Rank 12/51

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

Callstack Apex 100.0/100Rank 43/511 of 5 levels

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

Points per level

LevelGPT-6.1 TerraCallstack Apex
Level 1Hold the door
5.2 ptsCleared
5.2 ptsCleared
Level 2Crossfeed
9.8 ptsCleared
Pending
Level 3Relay vault
19.2 ptsCleared
Pending
Level 4Passing bay
17.8 ptsClearedFinished early · 3 beacons left
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

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.

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 TerraCallstack Apex
State at 600 ms23.0/2520.0/25
Camera and placement11.0/1513.0/15
Reflections33.0/12010.0/120
Materials and scale7.5/107.0/10
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

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.

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 TerraCallstack Apex
Task & likeness7.5/108.5/10
Anatomy & construction6.5/107.0/10
Space & placement6.5/107.5/10
Light & reflections6.0/107.5/10
Purposeful detail6.5/107.5/10
Artistry & character6.5/107.0/10
Materials & effects6.0/107.0/10
Visual integrity6.0/107.5/10

Benchmark task

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.

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

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.

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 TerraCallstack Apex
Task & likeness5.5/103.5/10
Anatomy & construction6.5/104.0/10
Space & placement4.5/104.5/10
Light & reflections6.5/106.0/10
Purposeful detail6.0/104.5/10
Artistry & character6.0/104.5/10
Materials & effects6.0/105.5/10
Visual integrity6.5/105.5/10

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

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.

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 TerraCallstack Apex
Task & likeness8.5/108.5/10
Anatomy & construction7.5/104.5/10
Space & placement6.5/107.5/10
Light & reflections5.5/105.5/10
Purposeful detail7.5/107.5/10
Artistry & character7.0/106.5/10
Materials & effects6.5/107.0/10
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

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

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.

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 TerraCallstack Apex
Task & likeness6.5/109.0/10
Anatomy & construction5.5/107.0/10
Space & placement6.0/107.5/10
Light & reflections5.0/107.0/10
Purposeful detail7.0/108.5/10
Artistry & character6.0/107.5/10
Materials & effects6.0/107.0/10
Visual integrity7.0/108.0/10

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

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.

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 TerraCallstack Apex
Task & likeness7.0/108.5/10
Anatomy & construction7.0/106.5/10
Space & placement6.0/107.5/10
Light & reflections5.5/107.5/10
Purposeful detail7.0/108.0/10
Artistry & character6.5/108.0/10
Materials & effects5.5/107.5/10
Visual integrity6.0/108.0/10

Benchmark task

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