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Comparison · 2 models · Updated Oct 4, 2026

Claude Sonnet 5.5 vs GPT-5.3 Codex

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

  1. 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

  2. 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

  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 inputsClaude Sonnet 5.5: Text, Images, PDFs · GPT-5.3 Codex: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightClaude Sonnet 5.5GPT-5.3 Codex
CapabilityCapabilities Index (ECI)50%9787
Price25%2118
Inputs & features15%8080
Context window10%6044
Overall100%72/10064/100
02 — Side by side

Every spec in one table

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

Claude Sonnet 5.5 vs GPT-5.3 Codex specifications side by side
SpecificationClaude Sonnet 5.5AnthropicGPT-5.3 CodexOpenAI
Capability
Capabilities Index (ECI)165.2 (best)156.8
ECI rank#3 of 148 (best)#18 of 148
GPQA DiamondGraduate-level science questions95.6%—
FrontierMath Tiers 1–3Research-level mathematics88.8%—
OTIS Mock AIME 2024–2025Competition mathematics100%—
SWE-bench VerifiedFixing real GitHub issues—74.8%
SimpleQA VerifiedShort factual questions46.5%—
Price per million tokens
Input$2.00$1.75 (best)
Output$10.00 (best)$14.00
Cached input$0.20$0.175 (best)
Blended (3:1)$4.00 (best)$4.81
Long-context rateSame rateSame rate
Price sourceOfficial Anthropic APIOfficial OpenAI API
Limits
Context window1,000,000 tokens (best)400,000 tokens
Max output128,000 tokens128,000 tokens
Inputs and features
TextYesYes
ImagesYesYes
PDFsYesYes
AudioNoNo
VideoNoNo
ReasoningYeslow · medium · high · xhigh · maxYeslow · medium · high · xhigh
Tool callingYesYes
Structured outputYesYes
Availability
WeightsProprietaryProprietary
API model IDclaude-sonnet-5-5gpt-5.3-codex
API providers23 (best)19
ReleasedSep 28, 2026Feb 5, 2026
Knowledge cutoffJun 2026Aug 31, 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.

  • Claude Sonnet 5.5$40.00
  • GPT-5.3 Codex$45.50
04 — Questions

Which should you choose?

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

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, Claude Sonnet 5.5 or GPT-5.3 Codex?

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: Claude Sonnet 5.5 up to 128,000, GPT-5.3 Codex up to 128,000 tokens.

Which can read images, PDFs, audio or video?

Claude Sonnet 5.5 accepts text, images and PDFs; GPT-5.3 Codex accepts text, images and PDFs. They handle the same number of input types.

Are any of these open source?

No. Claude Sonnet 5.5 and GPT-5.3 Codex 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: Claude Sonnet 5.5 Jun 2026, GPT-5.3 Codex Aug 31, 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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