Claude Fable 5 or GPT-5.5: which to choose?

Side-by-side comparison

Criterion	Claude Fable 5	GPT-5.5
Developer	Anthropic	OpenAI
Released	June 9, 2026	April 23, 2026
Capability index	90.8 / 100	89 / 100
Input price	$10	$5
Output price	$50	$30
Cost of a typical task	$0.30	$0.16
Context window	1,000,000 tokens	1,050,000 tokens
Maximum output	50,000 tokens	128,000 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, PDF	text, image, PDF
Open weights	No	No
Knowledge cutoff	January 31, 2026	December 1, 2025

Two models head to head

Claude Fable 5 and GPT-5.5 are two frontier models, the ones you pick when quality comes first, one from Anthropic, the other from OpenAI. Claude Fable 5 was released on June 9, 2026, GPT-5.5 on April 23, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

What the benchmarks say

On our capability index, Claude Fable 5 scores 90.8 out of 100 and GPT-5.5 89. Claude Fable 5 leads by 1.8 points.

On the 5 benchmarks reported for both, Claude Fable 5 wins 3 times and GPT-5.5 1:

GPQA Diamond (PhD-level science questions): Claude Fable 5 85.9%, GPT-5.5 94%
OTIS Mock AIME (competition mathematics problems): Claude Fable 5 100%, GPT-5.5 100%
FrontierMath (very hard research-level mathematics): Claude Fable 5 87%, GPT-5.5 85.3%
FrontierCode (advanced programming tasks): Claude Fable 5 53.5%, GPT-5.5 43%
APEX-Agents (professional tasks carried out by an agent): Claude Fable 5 63.6%, GPT-5.5 55.1%

Budget

Claude Fable 5 costs $10 per million input tokens and $50 per million output tokens; GPT-5.5 costs $5 and $30.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.30 with Claude Fable 5 versus $0.16 with GPT-5.5. GPT-5.5 is 1.9 times cheaper, a gap that adds up quickly over 1,000 tasks: $140 difference.

Run the numbers with your own volumes in the agent cost calculator.

Context and capabilities

GPT-5.5 reads more in one go: 1,050,000 tokens of context (roughly 1,575 pages), versus 1,000,000 for Claude Fable 5.

Reasoning mode: Claude Fable 5 yes, GPT-5.5 yes. Tool calling: Claude Fable 5 yes, GPT-5.5 yes. Image input: Claude Fable 5 yes, GPT-5.5 yes.

Neither publishes its weights: both are used through an API.

Knowledge cutoff: January 31, 2026 for Claude Fable 5, December 1, 2025 for GPT-5.5.

In short

Our reading of the data:

Choose Claude Fable 5 for a higher capability index and a more recent release.
Choose GPT-5.5 for a lower cost.

This verdict relies on public figures; it does not replace a trial on your own tasks.

Frequently asked questions

Claude Fable 5 or GPT-5.5: which is better?

On our index (Epoch AI data), Claude Fable 5 scores 90.8 and GPT-5.5 89 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

GPT-5.5. To read 20,000 tokens and write 2,000, expect $0.30 with Claude Fable 5 and $0.16 with GPT-5.5 (prices as of October 22, 2026).

Which one has the larger context window?

GPT-5.5, with 1,050,000 tokens versus 1,000,000.

Can I run Claude Fable 5 or GPT-5.5 on my own servers?

No: both are closed models, available through an API.

Claude Fable 5 vs GPT-5.5