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Comparison · 2 models · Updated Oct 4, 2026

GPT-5.3 Codex vs Claude Opus 4.5

GPT-5.3 Codex comes out ahead, 64 to 55 on our weighted score, and it is the cheaper option too.

  1. Our pick

    OpenAI

    GPT-5.3 Codex

    Released Feb 5, 2026

    64/100
    • ECI156.8
    • Price$1.75 / $14.00
    • Context400K
    Full specs Remove GPT-5.3 Codex

  2. Anthropic

    Claude Opus 4.5

    Released Nov 24, 2025

    55/100
    • ECI150.1
    • Price$5.00 / $25.00
    • Context200K
    Full specs Remove Claude Opus 4.5

  3. Add a model

    Make it a three-way comparison.

01 — Verdict

GPT-5.3 Codex is our pick

GPT-5.3 Codex is the better all-round choice, scoring 64/100 against Claude Opus 4.5 (55). It leads on capability, price and context window. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityGPT-5.3 CodexCapabilities Index (ECI): GPT-5.3 Codex 156.8 · Claude Opus 4.5 150.1
  • Lowest priceGPT-5.3 CodexGPT-5.3 Codex $4.81 · Claude Opus 4.5 $10.00 per 1M tokens (3:1 blend)
  • Longest contextGPT-5.3 CodexGPT-5.3 Codex 400,000 · Claude Opus 4.5 200,000 tokens
  • Widest inputsSame inputsGPT-5.3 Codex: Text, Images, PDFs · Claude Opus 4.5: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.3 CodexClaude Opus 4.5
CapabilityCapabilities Index (ECI)50%8778
Price25%182
Inputs & features15%8080
Context window10%4432
Overall100%64/10055/100
02 — Side by side

Every spec in one table

Highlighted cells lead their row. Dashes mean the data is not published.

GPT-5.3 Codex vs Claude Opus 4.5 specifications side by side
SpecificationGPT-5.3 CodexOpenAIClaude Opus 4.5Anthropic
Capability
Capabilities Index (ECI)156.8 (best)150.1
ECI rank#18 of 148 (best)#48 of 148
GPQA DiamondGraduate-level science questions—86.1%
FrontierMath Tiers 1–3Research-level mathematics—34.4%
OTIS Mock AIME 2024–2025Competition mathematics—86.1%
SWE-bench VerifiedFixing real GitHub issues74.8%76.7% (best)
SimpleQA VerifiedShort factual questions—45.7%
Price per million tokens
Input$1.75 (best)$5.00
Output$14.00 (best)$25.00
Cached input$0.175 (best)$0.50
Blended (3:1)$4.81 (best)$10.00
Long-context rateSame rateSame rate
Price sourceOfficial OpenAI APIOfficial Anthropic API
Limits
Context window400,000 tokens (best)200,000 tokens
Max output128,000 tokens (best)64,000 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoNo
ReasoningYeslow · medium · high · xhighYeslow · medium · high
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDgpt-5.3-codexclaude-opus-4-5
API providers1928 (best)
ReleasedFeb 5, 2026Nov 24, 2025
Knowledge cutoffAug 31, 2025May 2025
03 — Cost

What would a month cost?

Enter your expected volume in millions of tokens. List prices only; caching and batch discounts would lower these.

  • GPT-5.3 Codex$45.50
  • Claude Opus 4.5$100.00
04 — Questions

Which should you choose?

Which is better: GPT-5.3 Codex or Claude Opus 4.5?

GPT-5.3 Codex is the better all-round choice, scoring 64/100 against Claude Opus 4.5 (55). It leads on capability, price and context window. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.3 Codex or Claude Opus 4.5?

GPT-5.3 Codex is cheaper at $1.75 input / $14.00 output per million tokens (official OpenAI API price). Claude Opus 4.5 costs $5.00 input / $25.00 output per million tokens (official Anthropic API price). At a typical mix of three input tokens to one output token, that is $4.81 per million tokens for GPT-5.3 Codex versus $10.00 for Claude Opus 4.5 (2.1× as much).

Which scores higher on benchmarks?

GPT-5.3 Codex scores higher on the Capabilities Index (ECI): GPT-5.3 Codex 156.8 (#18 of 148) and Claude Opus 4.5 150.1 (#48 of 148). Their confidence ranges do not overlap (153.5–160.8 vs 147.9–153.0), so the gap is a real one. On individual benchmarks: SWE-bench Verified — Claude Opus 4.5 76.7%, GPT-5.3 Codex 74.8%.

Which is better for coding?

Claude Opus 4.5 resolves more real GitHub issues on SWE-bench Verified: Claude Opus 4.5 76.7% and GPT-5.3 Codex 74.8%. Both support tool calling for agent workflows.

Which has the bigger context window?

GPT-5.3 Codex has the largest context window at 400,000 tokens, against 200,000 for Claude Opus 4.5. Maximum output per response: GPT-5.3 Codex up to 128,000, Claude Opus 4.5 up to 64,000 tokens.

Which can read images, PDFs, audio or video?

GPT-5.3 Codex accepts text, images and PDFs; Claude Opus 4.5 accepts text, images and PDFs. They handle the same number of input types.

Are any of these open source?

No. GPT-5.3 Codex and Claude Opus 4.5 are proprietary and only available through APIs and apps.

Which is newer?

GPT-5.3 Codex is the newest, released Feb 5, 2026. Claude Opus 4.5 came out Nov 24, 2025. Knowledge cutoff: GPT-5.3 Codex Aug 31, 2025, Claude Opus 4.5 May 2025.

How do you decide the winner?

Each model gets a 0–100 score on capability (50%, independent benchmark results); price (25%, blended price per million tokens (3 input : 1 output), log scale); inputs & features (15%, image, PDF, audio and video input, tool calling, structured output and reasoning); context window (10%, maximum tokens per request, log scale). Dimensions missing for any model are dropped and the remaining weights rescaled, so every model is judged on the same evidence. Specs and prices come from public model listings and the labs’ own API pages; capability scores come from independent benchmark runs. Data updated Oct 4, 2026.

05 — Keep comparing

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