ResearchLLM Verifications Leaderboard

Data as of · 78 models, 80 questions · reviewed by Suhas Bhairav · methodology

Head to head · tested 27 Oct 2026

Claude Fable 5.1 vs GPT-5.3-Codex: accuracy, speed and price

Similar accuracy; GPT-5.3-Codex costs less per question.

AnthropicClaude Fable 5.181.2% score · #5$0.016 per question70 tok/sOpenAIGPT-5.3-Codex82.5% score · #3$0.01 per question95 tok/s

Verdict

Built from the measurements below

  • Accuracy is too close to call: Claude Fable 5.1 scored 81.2% and GPT-5.3-Codex 82.5% on the same 80 questions, a gap within what chance alone could produce.
  • GPT-5.3-Codex is 1.6× cheaper per question as billed ($0.01 vs $0.016), reasoning tokens included.
  • GPT-5.3-Codex generates text 1.4× faster: 95 tokens per second against 70.
  • GPT-5.3-Codex starts answering sooner: 1.4 s to the first token, against 2.1 s for Claude Fable 5.1.
  • Claude Fable 5.1 accepts more context: 1M tokens against 400k.

Which should you choose?

Choose Claude Fable 5.1 for shorter outputs (about 238 tokens per question against 699), a 1M-token context window and more hosts to choose from on OpenRouter (4 against 2). Choose GPT-5.3-Codex for the lower cost per correct answer ($0.013 against $0.02), faster streaming and a quicker first token.

Accuracy gap -1.2 points (z = -0.21). A winner is called only when z is at least 1.96, the usual 95% threshold. Speed, latency and price need a 10% margin.

Head to head

Same questions, same prompt, same API

MeasureClaude Fable 5.1GPT-5.3-CodexEdge
Verification scoreHigher is better81.2%82.5%Too close to call
Cost per questionLower is better$0.016$0.01GPT-5.3-Codex
Output speedHigher is better7095GPT-5.3-Codex
Time to first tokenLower is better2.1 s1.4 sGPT-5.3-Codex
End-to-end response timeLower is better11.0 s5.2 sGPT-5.3-Codex
Tokens per questionLower is better238699Claude Fable 5.1
Context windowHigher is better1M400kClaude Fable 5.1

Side by side

Bars are scaled to the larger of the two values. The winner on each measure is marked in bold.

Every measure

Claude Fable 5.1 first, GPT-5.3-Codex second

Verification scorehigher is better
Claude Fable 5.181.2%
GPT-5.3-Codex82.5%
Cost per questionlower is better
Claude Fable 5.1$0.016
GPT-5.3-Codex$0.01
Output speedhigher is better
Claude Fable 5.170
GPT-5.3-Codex95
Time to first tokenlower is better
Claude Fable 5.12.1 s
GPT-5.3-Codex1.4 s
End-to-end response timelower is better
Claude Fable 5.111.0 s
GPT-5.3-Codex5.2 s
Tokens per questionlower is better
Claude Fable 5.1238
GPT-5.3-Codex699
Context windowhigher is better
Claude Fable 5.11M
GPT-5.3-Codex400k

Score vs. cost per question

Both models in color, every other model in grey

Most attractive quadrant0255075100$0.00001$0.0001$0.001$0.01$0.10Cost per question (USD, log) →Verification score (%) →Qwen3.8 2.4T A95BCommand AReka Flash 3Gemma 4 26B A4BGemma 4 31BQwen3.5 397B A17BHermes 4 405BClaude Fable 5.1Grok 4.7o3gpt-oss-20bMinistral 3 3B 2512Nova Micro 1.0Phi 4Granite 4.2 8BHy3GLM 5.3 FlashSolar Pro 4Trinity Large ThinkingMiniMax M3Mistral Large 4Claude Opus 5.5GPT-6.1 SolGPT-6 Lunagpt-oss-120bLlama 4 MaverickQwen3.8 Max (0902)

Specifications and pricing

From OpenRouter's catalogue, plus the leaderboard's test dates

SpecificationClaude Fable 5.1GPT-5.3-Codex
CreatorAnthropicOpenAI
Released1 Sept 202624 Feb 2026
Weights——
ReasoningYesYes
Inputtext, image, filetext, image, file
Outputtexttext
Context window1M tokens400k tokens
Knowledge cutoff——
List price in / out per 1M$10 / $50$1.75 / $14
Blended price per 1M (3:1)$20.00$4.81
Cheapest hostAzure · $10 / $50Azure · $1.75 / $14
Hosts on OpenRouter42
Last tested27 Oct 202627 Oct 2026

Compare any two models →

Claude Fable 5.1 vs GPT-5.3-Codex: frequently asked questions

Is Claude Fable 5.1 better than GPT-5.3-Codex?
On accuracy they are statistically tied: Claude Fable 5.1 scored 81.2% and GPT-5.3-Codex 82.5% on the same 80 questions from open datasets. Similar accuracy; GPT-5.3-Codex costs less per question.
Which is cheaper, Claude Fable 5.1 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper: $0.01 per question as billed, against $0.016. List prices: Claude Fable 5.1 $10 in / $50 out, GPT-5.3-Codex $1.75 in / $14 out per million tokens.
Which is faster, Claude Fable 5.1 or GPT-5.3-Codex?
GPT-5.3-Codex is faster at 95 output tokens per second, against 70. Time to first token: 2.1 s for Claude Fable 5.1, 1.4 s for GPT-5.3-Codex.
Which has the larger context window, Claude Fable 5.1 or GPT-5.3-Codex?
Claude Fable 5.1, with 1M tokens against 400k.