Model comparison

Claude Fable 5 vs GPT-5.3-Codex

Anthropic against OpenAI, compared on context, price, and verified benchmark results.

Catalog record checked September 3, 2026Individual provider fields may changeEvidence confidence: High — see receipts below

Anthropic

Claude Fable 5

Frontier

OpenAI

GPT-5.3-Codex

Frontier

AI model capability comparison
Specification	Claude Fable 5	GPT-5.3-Codex
Provider	Anthropic	OpenAI
Tier	Frontier	Frontier
Context window	Winner: 1M	400K
Max output	128K	128K
Input / 1M tokens	$10	Winner: $1.75
Output / 1M tokens	$50	Winner: $14
Weights	Closed	Closed
Parameters	Not disclosedUnverified	Not disclosedUnverified
Reasoning levels	adaptive	none, low, medium, high, xhigh, max
Modalities	text, image	text, image
API model id	claude-fable-5	gpt-5.3-codex
Released	June 9, 2026	February 5, 2026
Artificial Analysis Intelligence Index (2026-08-14)	62	Not verifiedUnverified
Artificial Analysis Intelligence Index [high] (2026-08-14)	Not verifiedUnverified	52

Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Bold indicates the better figure where one is objectively better. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

2026-08-14: Artificial AnalysisComposite index blending reasoning, knowledge, and coding evals into one 0–100 score. Comparability: directly comparable — AA occasionally rebaselines the index scale between snapshots — a score captured on one date is only comparable to same-snapshot scores (check measuredAt).

Pricing tiers: Claude Fable 5: Standard $10/$50 per MTok; cache reads 10% of base input. Sibling Claude Mythos 5 is invite-only cyber-defense. Access briefly suspended 2026-06-12, redeployed 2026-07-01. · GPT-5.3-Codex: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent.

FrontierRecord checked September 3, 2026

Claude Fable 5

Claude Fable 5 is Anthropic's next-generation intelligence model for long-running agents, topped LiveBench until the 5.1 refresh.

Best for

Long-running agents
Frontier reasoning
Enterprise work

Watch out

Most expensive Anthropic tier at $10/$50; verify the cost is justified by the task.

FrontierRecord checked September 3, 2026

GPT-5.3-Codex

GPT-5.3-Codex is OpenAI's coding-specialised model powering the Codex agent at $1.75/$14.

Best for

Autonomous coding
Repo-scale refactors
Test generation

Watch out

Tuned for coding, not general chat; use GPT-5.6 for broad reasoning.

When the cheaper one wins

GPT-5.3-Codex is cheaper on output at $14 per million tokens against $50 for Claude Fable 5 — about 3.6×. Use the cheaper tier for classification, extraction, summarisation, and any task where the expensive model’s extra score does not change the accepted output. The expensive one only pays if your hardest task actually fails on the cheap tier. These are standard-tier API rates, excluding batch and cache discounts.

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Evidence confidence: High

How strong and complete the evidence behind this comparison is — not a prediction of which model is better.

Pricing verified on both sides — Input and output rates are verified for both models.
4/5 core specs verified on both sides — Not published for at least one side: parameter count.
1 shared named benchmark with differing scores — Measured on: Artificial Analysis Intelligence Index.
Verified within the last 90 days — Newest catalog check was 8 days ago.
Both models carry source citations — Each side has at least two catalog sources on record.

Source receipts

Each catalog figure was checked against the provider or an independent second source on the date shown.

Claude Fable 5: Anthropic — Claude Fable 5 (accessed 2026-08-29)
Claude Fable 5: Anthropic news — Claude Fable 5 (accessed 2026-08-29)
GPT-5.3-Codex: OpenAI — Introducing GPT-5.3-Codex (accessed 2026-08-29)
GPT-5.3-Codex: OpenAI API pricing (gpt-5.3-codex $1.75/$14) (accessed 2026-08-29)

Related comparisons

Diving deeper on one model? Claude Fable 5 · GPT-5.3-Codex

Common questions

Claude Fable 5 vs GPT-5.3-Codex

Answered from the verified figures on this page rather than general guidance.

Is Claude Fable 5 or GPT-5.3-Codex cheaper for input?

GPT-5.3-Codex is cheaper at $1.75 per million input tokens, against $10 for Claude Fable 5 — roughly 5.7× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Fable 5 has tiered pricing: Standard $10/$50 per MTok; cache reads 10% of base input. Sibling Claude Mythos 5 is invite-only cyber-defense. Access briefly suspended 2026-06-12, redeployed 2026-07-01. GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent.

Is Claude Fable 5 or GPT-5.3-Codex cheaper for output?

GPT-5.3-Codex is cheaper at $14 per million output tokens, against $50 for Claude Fable 5 — roughly 3.6× the price. Output tokens usually dominate a real bill, so weigh the output rate more heavily than the input rate. These are base rates; Claude Fable 5 has tiered pricing: Standard $10/$50 per MTok; cache reads 10% of base input. Sibling Claude Mythos 5 is invite-only cyber-defense. Access briefly suspended 2026-06-12, redeployed 2026-07-01. GPT-5.3-Codex has tiered pricing: Standard $1.75/$14 per MTok; cached input $0.175/MTok; Fast mode $3.50/$28. Purpose-built for the Codex agent.

Which has the larger context window, Claude Fable 5 or GPT-5.3-Codex?

Claude Fable 5 accepts 1M tokens against 400K for GPT-5.3-Codex. This only matters if you routinely send very long documents or large codebases.

Do Claude Fable 5 and GPT-5.3-Codex support the same reasoning levels?

Claude Fable 5 exposes adaptive, while GPT-5.3-Codex exposes none, low, medium, high, xhigh, max.

Should I use Claude Fable 5 or GPT-5.3-Codex?

Both sit in the frontier tier, so the choice usually comes down to price and context rather than capability. Claude Fable 5 suits long-running agents; GPT-5.3-Codex suits autonomous coding.

Next step

Choosing between them

The verified figures that separate this pair, computed from the catalog rather than restated boilerplate.

Input price: GPT-5.3-Codex costs $1.75 per 1M tokens versus $10 for Claude Fable 5 — a 5.7x difference at the headline tier.
Context: Claude Fable 5 takes 1M against 400K for GPT-5.3-Codex — only decisive if your prompts approach the smaller window.

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