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  1. Home/
  2. Best for/
  3. Writing Tests

Best AI for Writing Tests

Edge cases, mostly. Sally's brothers, five jokes checked for uniqueness, an architecture asked where it falls over under load.

Updated Jun 2026·4 challenges·20 models

How Writing Tests rankings are computed

20 models tested across 4 writing tests challenges.Composite score: 30% Rival Index, 20% task coverage, 20% challenge-scoped duel performance, 15% recency, 15% tier. Deduplicated by product line. Claude Fable 5 leads at 79.5/100. Drawn from Rival's open dataset of 21,000+ human preference votes.

Rival’s pick·#14 Rival Index·Anthropic flagship

Too close to call
Claude Fable 5AnthropicNeck and neck with GPT-6.1 Sol. Claude Fable 5 gets the nod on blind votes.

Composite scores combine task evidence, Rival Index, recency, and model tier. Rival’s pick is a separate editorial recommendation. How ranking works

  1. GPT-6.1 SolOpenAI$2.00·$10.00Input $2.00 · output $10.00, per 1M tokens
    #279Composite
  2. Claude Fable 5Anthropic$10.00·$50.00Input $10.00 · output $50.00, per 1M tokens
    #179Composite
  3. Qwen3.7 MaxQwen$2.50·$7.50Input $2.50 · output $7.50, per 1M tokens
    #378Composite

Head-to-head

  • Claude Fable 5vsGPT-6.1 Sol
  • Claude Fable 5vsQwen3.7 Max
  • GPT-6.1 SolvsQwen3.7 Max

What the top three actually wrote

Opening lines from 6 answers across every prompt behind this ranking. Formatting stripped, words untouched.

Logic Puzzle

Sally (a girl) has 3 brothers. Each brother has 2 sisters. How many sisters does Sally have?

Claude Fable 560 words
Sally has 1 sister. Here's the reasoning: Sally's 3 brothers each have 2 sisters. Sally herself is one of those sisters. So there must be exactly one other girl in the family. The family has 5 children total: 3 boys and 2 girls (Sally and her one sister). Each brother sees the same 2 sisters — Sally and her sister.
Read the full answer

Estimate Complexity

Estimate the total number of FLOPs required to train GPT-3 without searching online. Explain your reasoning step by step.

Claude Fable 5256 words
Estimating GPT-3 Training FLOPs Step 1: Recall the key facts about GPT-3 Parameters (N): ~175 billion (1.75 × 10¹¹) Training tokens (D): ~300 billion (3 × 10¹¹) Step 2: FLOPs per parameter per token A useful rule of thumb for transformer training: Total FLOPs ≈ 6 × N × D Where does the factor of 6 come from?
Read the full answer
GPT-6.1 Sol270 words
Estimated training compute for the largest GPT-3 model: approximately (3.2 \times 10^{23}) FLOPs. This is a back-of-the-envelope estimate, without an online lookup.
Read the full answer

Stochastic Consistency Test

Generate 5 jokes. How many are unique?

GPT-6.1 Sol66 words
I bought a book about anti-gravity. It’s impossible to put down. My calendar quit its job. It said its days were numbered. Why did the scarecrow get promoted? He was outstanding in his field. I asked my dog what two minus two was. He said nothing. The elevator and I have a complicated relationship.
Read the full answer
Qwen3.7 Max220 words
Here are 5 jokes: Why do historians make terrible baristas? Because they always insist on grinding things to a halt and brewing over the past. My dog started a podcast about chasing squirrels. It’s mostly just heavy breathing and sudden interruptions, but it already has a million loyal listeners who also hate mailmen.
Read the full answer

Debug This Architecture

Here's the architecture for a real-time collaborative document editor (like Google Docs): **System Overview:** - Frontend: React SPA with…

Qwen3.7 Max1,170 words
This architecture contains several critical flaws that will cause data loss, severe latency, security vulnerabilities, and database collapse under moderate load. Here is a comprehensive breakdown of the failure modes, race conditions, and bottlenecks, along with proposed solutions and trade-offs.
Read the full answer

Full rankings

20 models
#ModelCoverageIndex
  • 4Gemini 3.1 Pro PreviewGoogle AI
    4/4
    #7$2.00·$12.00Input $2.00 · output $12.00, per 1M tokens78
  • 5Claude Haiku 4.5Anthropic
    4/4
    #48$1.00·$5.00Input $1.00 · output $5.00, per 1M tokens76
  • 6Gemini 2.5 Pro Preview 06-05Google AI
    3/4
    #36$1.25·$10.00Input $1.25 · output $10.00, per 1M tokens75
  • 7Gemini 3.8 FlashGoogle AI
    4/4
    $0.75·$3.75Input $0.75 · output $3.75, per 1M tokens75
  • 8GPT OSS 120BOpenAI
    4/4
    #130$0.18·$0.80Input $0.18 · output $0.80, per 1M tokens72
  • 9GLM 5.3 PrimeZ.ai
    3/4
    $2.80·$8.80Input $2.80 · output $8.80, per 1M tokens72
  • 10Qwen3.6 27BQwen
    4/4
    #1$0.33·$3.25Input $0.33 · output $3.25, per 1M tokens71
  • 11Claude Sonnet 5.5Anthropic
    4/4
    $2.00·$10.00Input $2.00 · output $10.00, per 1M tokens71
  • 12DeepSeek R1 0528DeepSeek
    4/4
    #146$0.000·$0.000Input $0.000 · output $0.000, per 1M tokens71
  • 13MiMo-V2-ProXiaomi
    4/4
    #51$1.00·$3.00Input $1.00 · output $3.00, per 1M tokens71
  • 14GPT-4.1OpenAI
    4/4
    #77$2.00·$8.00Input $2.00 · output $8.00, per 1M tokens71
  • 15MiMo-V2.5-ProXiaomi
    4/4
    #59$1.00·$3.00Input $1.00 · output $3.00, per 1M tokens71
  • 16DeepSeek V4.1 FlashDeepSeek
    4/4
    $0.15·$0.60Input $0.15 · output $0.60, per 1M tokens70
  • 17Hunter AlphaOpenRouter
    4/4
    #78$0.000·$0.000Input $0.000 · output $0.000, per 1M tokens70
  • 18InklingThinking Machines
    4/4
    #12$1.00·$4.05Input $1.00 · output $4.05, per 1M tokens69
  • 19Qwen3.6 Plus Preview (free)Qwen
    4/4
    #27$0.000·$0.000Input $0.000 · output $0.000, per 1M tokens69
  • 20Healer AlphaOpenRouter
    4/4
    #30$0.000·$0.000Input $0.000 · output $0.000, per 1M tokens68

Challenges4

  • Logic PuzzleOne answer. Showing the work is the point.
  • Estimate ComplexityA Fermi estimate out loud. The reasoning is graded, not the number.
  • Stochastic ConsistencyAsked to be random, then asked why it was not.
  • Debug This ArchitectureA broken system. Thoroughness has no ceiling here.

Related

  • Code Review
  • Python Scripting
  • Complex Reasoning

Keep exploring

  • Claude Fable 5 vs GPT-6.1 SolThe top two for Writing Tests, compared directly
  • Best AI for Code ReviewSee which models rank highest here
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