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Comparison · 2 models · Updated Oct 4, 2026

GPT-5.3 Codex vs Claude Sonnet 5.5

Claude Sonnet 5.5 comes out ahead, 72 to 64 on our weighted score, and it is the cheaper option too.

  1. 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. Our pick

    Anthropic

    Claude Sonnet 5.5

    Released Sep 28, 2026

    72/100
    • ECI165.2
    • Price$2.00 / $10.00
    • Context1M
    Full specs Remove Claude Sonnet 5.5

  3. Add a model

    Make it a three-way comparison.

01 — Verdict

Claude Sonnet 5.5 is our pick

Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against GPT-5.3 Codex (64). It leads on capability, price and context window. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityClaude Sonnet 5.5Capabilities Index (ECI): Claude Sonnet 5.5 165.2 · GPT-5.3 Codex 156.8
  • Lowest priceClaude Sonnet 5.5Claude Sonnet 5.5 $4.00 · GPT-5.3 Codex $4.81 per 1M tokens (3:1 blend)
  • Longest contextClaude Sonnet 5.5Claude Sonnet 5.5 1,000,000 · GPT-5.3 Codex 400,000 tokens
  • Widest inputsSame inputsGPT-5.3 Codex: Text, Images, PDFs · Claude Sonnet 5.5: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.3 CodexClaude Sonnet 5.5
CapabilityCapabilities Index (ECI)50%8797
Price25%1821
Inputs & features15%8080
Context window10%4460
Overall100%64/10072/100
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 Sonnet 5.5 specifications side by side
SpecificationGPT-5.3 CodexOpenAIClaude Sonnet 5.5Anthropic
Capability
Capabilities Index (ECI)156.8165.2 (best)
ECI rank#18 of 148#3 of 148 (best)
GPQA DiamondGraduate-level science questions—95.6%
FrontierMath Tiers 1–3Research-level mathematics—88.8%
OTIS Mock AIME 2024–2025Competition mathematics—100%
SWE-bench VerifiedFixing real GitHub issues74.8%—
SimpleQA VerifiedShort factual questions—46.5%
Price per million tokens
Input$1.75 (best)$2.00
Output$14.00$10.00 (best)
Cached input$0.175 (best)$0.20
Blended (3:1)$4.81$4.00 (best)
Long-context rateSame rateSame rate
Price sourceOfficial OpenAI APIOfficial Anthropic API
Limits
Context window400,000 tokens1,000,000 tokens (best)
Max output128,000 tokens128,000 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoNo
ReasoningYeslow · medium · high · xhighYeslow · medium · high · xhigh · max
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDgpt-5.3-codexclaude-sonnet-5-5
API providers1923 (best)
ReleasedFeb 5, 2026Sep 28, 2026
Knowledge cutoffAug 31, 2025Jun 2026
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 Sonnet 5.5$40.00
04 — Questions

Which should you choose?

Which is better: GPT-5.3 Codex or Claude Sonnet 5.5?

Claude Sonnet 5.5 is the better all-round choice, scoring 72/100 against GPT-5.3 Codex (64). 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 Sonnet 5.5?

Claude Sonnet 5.5 is cheaper at $2.00 input / $10.00 output per million tokens (official Anthropic API price). GPT-5.3 Codex costs $1.75 input / $14.00 output per million tokens (official OpenAI API price). At a typical mix of three input tokens to one output token, that is $4.00 per million tokens for Claude Sonnet 5.5 versus $4.81 for GPT-5.3 Codex (1.2× as much).

Which scores higher on benchmarks?

Claude Sonnet 5.5 scores higher on the Capabilities Index (ECI): Claude Sonnet 5.5 165.2 (#3 of 148) and GPT-5.3 Codex 156.8 (#18 of 148). Their confidence ranges do not overlap (161.8–169.4 vs 153.5–160.8), so the gap is a real one.

Which is better for coding?

There are no published SWE-bench Verified results for Claude Sonnet 5.5 yet, so there is no like-for-like coding score. On overall capability, Claude Sonnet 5.5 leads, which tends to carry over to coding, but test on your own codebase. Both support tool calling for agent workflows.

Which has the bigger context window?

Claude Sonnet 5.5 has the largest context window at 1,000,000 tokens, against 400,000 for GPT-5.3 Codex. Maximum output per response: GPT-5.3 Codex up to 128,000, Claude Sonnet 5.5 up to 128,000 tokens.

Which can read images, PDFs, audio or video?

GPT-5.3 Codex accepts text, images and PDFs; Claude Sonnet 5.5 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 Sonnet 5.5 are proprietary and only available through APIs and apps.

Which is newer?

Claude Sonnet 5.5 is the newest, released Sep 28, 2026. GPT-5.3 Codex came out Feb 5, 2026. Knowledge cutoff: GPT-5.3 Codex Aug 31, 2025, Claude Sonnet 5.5 Jun 2026.

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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