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Comparison · 2 models · Updated Oct 4, 2026

GPT-5.3 Codex vs Claude Fable 5

Too close to call on our weighted score (Claude Fable 5 65, GPT-5.3 Codex 64). The right pick depends on what you value most.

  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. Anthropic

    Claude Fable 5

    Released Jun 9, 2026

    65/100
    • ECI162.2
    • Price$10.00 / $50.00
    • Context1M
    Full specs Remove Claude Fable 5

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01 — Verdict

Too close to call

It is close. Our weighted score puts them within a point (Claude Fable 5 65/100, GPT-5.3 Codex 64/100), so choose by what matters most for your work: Claude Fable 5 for raw capability and GPT-5.3 Codex on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

  • CapabilityClaude Fable 5Capabilities Index (ECI): Claude Fable 5 162.2 · GPT-5.3 Codex 156.8
  • Lowest priceGPT-5.3 CodexGPT-5.3 Codex $4.81 · Claude Fable 5 $20.00 per 1M tokens (3:1 blend)
  • Longest contextClaude Fable 5Claude Fable 5 1,000,000 · GPT-5.3 Codex 400,000 tokens
  • Widest inputsSame inputsGPT-5.3 Codex: Text, Images, PDFs · Claude Fable 5: Text, Images, PDFs
  • Self-hostingNo open weightsBoth are available only through APIs
How the score is built
MeasureWeightGPT-5.3 CodexClaude Fable 5
CapabilityCapabilities Index (ECI)50%8794
Price25%180
Inputs & features15%8080
Context window10%4460
Overall100%64/10065/100
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 Fable 5 specifications side by side
SpecificationGPT-5.3 CodexOpenAIClaude Fable 5Anthropic
Capability
Capabilities Index (ECI)156.8162.2 (best)
ECI rank#18 of 148#7 of 148 (best)
GPQA DiamondGraduate-level science questions—85.9%
FrontierMath Tiers 1–3Research-level mathematics—87.0%
OTIS Mock AIME 2024–2025Competition mathematics—100%
SWE-bench VerifiedFixing real GitHub issues74.8%—
SimpleQA VerifiedShort factual questions—70.7%
Price per million tokens
Input$1.75 (best)$10.00
Output$14.00 (best)$50.00
Cached input$0.175 (best)$1.00
Blended (3:1)$4.81 (best)$20.00
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-fable-5
API providers1938 (best)
ReleasedFeb 5, 2026Jun 9, 2026
Knowledge cutoffAug 31, 2025Jan 31, 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 Fable 5$200.00
04 — Questions

Which should you choose?

Which is better: GPT-5.3 Codex or Claude Fable 5?

It is close. Our weighted score puts them within a point (Claude Fable 5 65/100, GPT-5.3 Codex 64/100), so choose by what matters most for your work: Claude Fable 5 for raw capability and GPT-5.3 Codex on price. The score weighs capability 50%, price 25%, inputs & features 15%, context window 10%.

Which is cheaper, GPT-5.3 Codex or Claude Fable 5?

GPT-5.3 Codex is cheaper at $1.75 input / $14.00 output per million tokens (official OpenAI API price). Claude Fable 5 costs $10.00 input / $50.00 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 $20.00 for Claude Fable 5 (4.2× as much).

Which scores higher on benchmarks?

Claude Fable 5 scores higher on the Capabilities Index (ECI): Claude Fable 5 162.2 (#7 of 148) and GPT-5.3 Codex 156.8 (#18 of 148). The confidence ranges of the top two overlap (159.6–166.1 vs 153.5–160.8), so treat the gap as small.

Which is better for coding?

There are no published SWE-bench Verified results for Claude Fable 5 yet, so there is no like-for-like coding score. On overall capability, Claude Fable 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 Fable 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 Fable 5 up to 128,000 tokens.

Which can read images, PDFs, audio or video?

GPT-5.3 Codex accepts text, images and PDFs; Claude Fable 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 Fable 5 are proprietary and only available through APIs and apps.

Which is newer?

Claude Fable 5 is the newest, released Jun 9, 2026. GPT-5.3 Codex came out Feb 5, 2026. Knowledge cutoff: GPT-5.3 Codex Aug 31, 2025, Claude Fable 5 Jan 31, 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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