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Comparison · 2 models · Updated Oct 4, 2026

GPT-5.5 Instant vs Claude Sonnet 4

Too close to call on our weighted score (Claude Sonnet 4 51, GPT-5.5 Instant 51). The right pick depends on what you value most.

  1. OpenAI

    GPT-5.5 Instant

    Released May 5, 2026

    51/100
    • ECI142.5
    • Price$5.00 / $30.00
    • Context400K
    Full specs Remove GPT-5.5 Instant

  2. Anthropic

    Claude Sonnet 4

    Released May 22, 2025

    51/100
    • ECI141.7
    • Price$3.00 / $15.00
    • Context200K
    Full specs Remove Claude Sonnet 4

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01 — Verdict

Too close to call

It is close. Our weighted score puts them within a point (Claude Sonnet 4 51/100, GPT-5.5 Instant 51/100), so choose by what matters most for your work: GPT-5.5 Instant for raw capability and Claude Sonnet 4 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityGPT-5.5 InstantCapabilities Index (ECI): GPT-5.5 Instant 142.5 · Claude Sonnet 4 141.7
  • Lowest priceClaude Sonnet 4Claude Sonnet 4 $6.00 · GPT-5.5 Instant $11.25 per 1M tokens (3:1 blend)
  • Longest contextGPT-5.5 InstantGPT-5.5 Instant 400,000 · Claude Sonnet 4 200,000 tokens
  • Widest inputsSame inputsGPT-5.5 Instant: Text, Images, PDFs · Claude Sonnet 4: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.5 InstantClaude Sonnet 4
CapabilityCapabilities Index (ECI)50%6968
Price25%013
Inputs & features15%8070
Context window10%4432
Overall100%51/10051/100
02 — Side by side

Every spec in one table

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

GPT-5.5 Instant vs Claude Sonnet 4 specifications side by side
SpecificationGPT-5.5 InstantOpenAIClaude Sonnet 4Anthropic
Capability
Capabilities Index (ECI)142.5 (best)141.7
ECI rank#89 of 148 (best)#94 of 148
GPQA DiamondGraduate-level science questions82.5% (best)79.2%
FrontierMath Tiers 1–3Research-level mathematics26.3%—
OTIS Mock AIME 2024–2025Competition mathematics68.1%71.1% (best)
Price per million tokens
Input$5.00$3.00 (best)
Output$30.00$15.00 (best)
Cached input——
Blended (3:1)$11.25$6.00 (best)
Long-context rateSame rateSame rate
Price sourceMedian of 3 providersMedian of 9 providers
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
ReasoningYesYes
Tool callingYesYes
Structured outputYesNo
Availability
WeightsProprietaryProprietary
API model ID——
API providers39 (best)
ReleasedMay 5, 2026May 22, 2025
Knowledge cutoffDec 1, 2025Mar 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.

  • GPT-5.5 Instant$110.00
  • Claude Sonnet 4$60.00
04 — Questions

Which should you choose?

Which is better: GPT-5.5 Instant or Claude Sonnet 4?

It is close. Our weighted score puts them within a point (Claude Sonnet 4 51/100, GPT-5.5 Instant 51/100), so choose by what matters most for your work: GPT-5.5 Instant for raw capability and Claude Sonnet 4 on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.5 Instant or Claude Sonnet 4?

Claude Sonnet 4 is cheaper at $3.00 input / $15.00 output per million tokens (median across 9 API providers). GPT-5.5 Instant costs $5.00 input / $30.00 output per million tokens (median across 3 API providers). At a typical mix of three input tokens to one output token, that is $6.00 per million tokens for Claude Sonnet 4 versus $11.25 for GPT-5.5 Instant (1.9× as much).

Which scores higher on benchmarks?

GPT-5.5 Instant scores higher on the Capabilities Index (ECI): GPT-5.5 Instant 142.5 (#89 of 148) and Claude Sonnet 4 141.7 (#94 of 148). The confidence ranges of the top two overlap (140.0–145.3 vs 139.2–142.9), so treat the gap as small. On individual benchmarks: GPQA Diamond — GPT-5.5 Instant 82.5%, Claude Sonnet 4 79.2%; OTIS Mock AIME 2024–2025 — Claude Sonnet 4 71.1%, GPT-5.5 Instant 68.1%.

Which is better for coding?

There are no published SWE-bench Verified results for GPT-5.5 Instant and Claude Sonnet 4 yet, so there is no like-for-like coding score. On overall capability, GPT-5.5 Instant 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?

GPT-5.5 Instant has the largest context window at 400,000 tokens, against 200,000 for Claude Sonnet 4. Maximum output per response: GPT-5.5 Instant up to 128,000, Claude Sonnet 4 up to 64,000 tokens.

Which can read images, PDFs, audio or video?

GPT-5.5 Instant accepts text, images and PDFs; Claude Sonnet 4 accepts text, images and PDFs. They handle the same number of input types.

Are any of these open source?

No. GPT-5.5 Instant and Claude Sonnet 4 are proprietary and only available through APIs and apps.

Which is newer?

GPT-5.5 Instant is the newest, released May 5, 2026. Claude Sonnet 4 came out May 22, 2025. Knowledge cutoff: GPT-5.5 Instant Dec 1, 2025, Claude Sonnet 4 Mar 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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