ResearchLLM Verifications Leaderboard

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

Head to head · tested 27 Oct 2026

Claude Opus 5.5 vs GPT-5.3-Codex: accuracy, speed and price

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

AnthropicClaude Opus 5.585.0% score · #1$0.015 per question129 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 Opus 5.5 scored 85.0% 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 1.4× cheaper per question as billed ($0.01 vs $0.015), reasoning tokens included.
  • Claude Opus 5.5 generates text 1.4× faster: 129 tokens per second against 95.
  • GPT-5.3-Codex starts answering sooner: 1.4 s to the first token, against 2.3 s for Claude Opus 5.5.
  • Claude Opus 5.5 accepts more context: 1M tokens against 400k.

Which should you choose?

Choose Claude Opus 5.5 for faster streaming, a 1M-token context window and more hosts to choose from on OpenRouter (5 against 2). Choose GPT-5.3-Codex for the lower cost per correct answer ($0.013 against $0.017) and a quicker first token.

Accuracy gap +2.5 points (z = 0.43). 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 Opus 5.5GPT-5.3-CodexEdge
Verification scoreHigher is better85.0%82.5%Too close to call
Cost per questionLower is better$0.015$0.01GPT-5.3-Codex
Output speedHigher is better12995Claude Opus 5.5
Time to first tokenLower is better2.3 s1.4 sGPT-5.3-Codex
End-to-end response timeLower is better7.6 s5.2 sGPT-5.3-Codex
Tokens per questionLower is better645699Similar
Context windowHigher is better1M400kClaude Opus 5.5

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 Opus 5.5 first, GPT-5.3-Codex second

Verification scorehigher is better
Claude Opus 5.585.0%
GPT-5.3-Codex82.5%
Cost per questionlower is better
Claude Opus 5.5$0.015
GPT-5.3-Codex$0.01
Output speedhigher is better
Claude Opus 5.5129
GPT-5.3-Codex95
Time to first tokenlower is better
Claude Opus 5.52.3 s
GPT-5.3-Codex1.4 s
End-to-end response timelower is better
Claude Opus 5.57.6 s
GPT-5.3-Codex5.2 s
Tokens per questionlower is better
Claude Opus 5.5645
GPT-5.3-Codex699
Context windowhigher is better
Claude Opus 5.51M
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 405BMuse WonderGrok 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 SolGemini 4 ArgonGPT-5.4GPT-6 Lunagpt-oss-120bLlama 4 Maverick

Specifications and pricing

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

SpecificationClaude Opus 5.5GPT-5.3-Codex
CreatorAnthropicOpenAI
Released22 Sept 202624 Feb 2026
Weights——
ReasoningYesYes
Inputtext, image, filetext, image, file
Outputtexttext
Context window1M tokens400k tokens
Knowledge cutoff——
List price in / out per 1M$4 / $20$1.75 / $14
Blended price per 1M (3:1)$8.00$4.81
Cheapest hostAmazon Bedrock · $4 / $20Azure · $1.75 / $14
Hosts on OpenRouter52
Last tested25 Oct 202627 Oct 2026

Compare any two models →

Claude Opus 5.5 vs GPT-5.3-Codex: frequently asked questions

Is Claude Opus 5.5 better than GPT-5.3-Codex?
On accuracy they are statistically tied: Claude Opus 5.5 scored 85.0% 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 Opus 5.5 or GPT-5.3-Codex?
GPT-5.3-Codex is cheaper: $0.01 per question as billed, against $0.015. List prices: Claude Opus 5.5 $4 in / $20 out, GPT-5.3-Codex $1.75 in / $14 out per million tokens.
Which is faster, Claude Opus 5.5 or GPT-5.3-Codex?
Claude Opus 5.5 is faster at 129 output tokens per second, against 95. Time to first token: 2.3 s for Claude Opus 5.5, 1.4 s for GPT-5.3-Codex.
Which has the larger context window, Claude Opus 5.5 or GPT-5.3-Codex?
Claude Opus 5.5, with 1M tokens against 400k.