Undominated.ai

Model comparison · accepted catalogue facts 2026-09-23

Claude Fable 5.1 vs GPT-6 Astra

Claude Fable 5.1 has an equal-or-higher measured score and an equal-or-lower estimated price. Switching from GPT-6 Astra loses capability or fails a requirement. Review the migration checks. The reported score intervals do not overlap; this is not a task-specific success guarantee.

Editorial comparison: Cross-provider reasoning shortlist: compare independent scores, context and priced request shapes before a migration. Inclusion does not recommend either model.

Claude Fable 5.1

LMArena general · Elo · higher is better

Scale starts at 1040 Elo

1507.6

Balanced effective USD / 1M tokens · lower is better

$20.00/M

GPT-6 Astra

LMArena general · Elo · higher is better

Scale starts at 1040 Elo

1443.7

Balanced effective USD / 1M tokens · lower is better

$20.00/M

Compare · model decision

Choose two or three models

Inspect the differences, estimate your workload and keep the evidence. All standard catalogue models are available, including unrated ones.

Catalogue facts
2026-09-23

2 / 3 selected · 0 requirements
Open public comparison link
Public workload and requirements

These settings are included in the share link. The fixed-request scenario and private evaluation data below are excluded.

A ↔ B

Claude Fable 5.1 has an equal-or-higher measured score and an equal-or-lower estimated price. Switching from GPT-6 Astra loses capability or fails a requirement. Review the migration checks. The reported score intervals do not overlap; this is not a task-specific success guarantee.

Estimated blend: 75% input, 25% output; 0% cached input. Base context tier. Prompt length selects the billing tier. An unlisted cache-read rate uses that tier’s full input rate in this blend; missing required input or output rates prevent an estimate. The fixed-request estimate below validates actual context and output limits and requires a published cache-read rate when cache hits are assumed.

What changes between these models

Quality first, then estimated price. LMArena scores are human-preference measurements, not a benchmark of your application. A missing score is unrated.

  • Claude Fable 5.1 · Meets the stated model requirements
  • GPT-6 Astra · Meets the stated model requirements
Material differences and unknown evidence. Deltas compare each model with model A. Unknown facts remain visible.
Measured factA Claude Fable 5.1B GPT-6 Astra
LMArena general score (Elo)1,507.61,443.7Δ vs A: -63.9 Elo
Score interval half-width (± Elo)8.1511.64Δ vs A: +3.49 Elo
LMArena document score (Elo)1,512.61,467.5Δ vs A: -45.1 Elo
Base cached-input USD / 1M tokens$0.25$1Δ vs A: +0.75 USD/M
Context window (tokens)1,000,0001,050,000Δ vs A: +50,000 tokens
Input modalitiestext, image, filefile, image, text
Open weightsUnknownUnknown
Recorded licenceUnknownUnknown
Model providerAnthropicOpenAI
Distinct sellers in the catalogue43Δ vs A: -1
Recorded retirement dateUnknownUnknown
9 shared measured facts
Shared measured facts. Deltas compare each model with model A. Unknown facts remain visible.
Measured factA Claude Fable 5.1B GPT-6 Astra
Benchmark reasoning effortmaxmax
Estimated effective USD / 1M tokens$20$20Δ vs A: 0 USD/M
Base input USD / 1M tokens$10$10Δ vs A: 0 USD/M
Base output USD / 1M tokens$50$50Δ vs A: 0 USD/M
Output limit (tokens)128,000128,000Δ vs A: 0 tokens
Tool useSupportedSupportedΔ vs A: 0
ReasoningSupportedSupportedΔ vs A: 0
Serving precision differs across offersNot supportedNot supportedΔ vs A: 0
Retirement evidenceNone announced; not a guaranteeNone announced; not a guarantee

Provider counts and precision flags describe catalogue offers. They do not establish the precision, availability, region, tool behaviour or limits of your chosen endpoint. Open each model’s provider table before switching.

Complete price ladders and billing conditions

Claude Fable 5.1

Rates below are USD per 1M tokens. A threshold selects that whole input/output rate pair.

Input-token thresholdInputOutputCached input
Base, up to and including first threshold$10$50$0.25

GPT-6 Astra

Rates below are USD per 1M tokens. A threshold selects that whole input/output rate pair.

Input-token thresholdInputOutputCached input
Base, up to and including first threshold$10$50$1
> 272,000$20$75$2
Migration preflight · compare each candidate with model A

Keeping Claude Fable 5.1 is a valid decision. No pairwise comparison certifies a drop-in replacement.

Claude Fable 5.1 → GPT-6 Astra

No known model-capability loss

  • Provider endpoint, serving precision, availability and task success need your own verification. Catalogue model capabilities do not certify an endpoint.
Check alternatives to Claude Fable 5.1

Estimate a fixed request shape

Private to this tab unless you save locally or explicitly export private details. These are estimates, not observed invoices. Cross-model token counts and task success are assumptions.

0.1 extra attempts means 10 extra full attempts per 100 requests. Cache writes, tool charges, taxes and unlisted charges are excluded.

  • Claude Fable 5.1Estimated total: $45 1,000 full attempts · base rates
  • GPT-6 AstraEstimated total: $45 1,000 full attempts · base rates
Prompt and output sensitivity · sampled scenarios

Every point recalculates the entire request shape. Tier-boundary samples include one token below, at and above each threshold. Ordering between samples is not guaranteed. Lowest known cost excludes unknown estimates and is not a replacement recommendation.

Vary input; hold output, requests, cache and retries fixed.
Input tokensClaude Fable 5.1GPT-6 AstraCoverage
2,000$45Lowest known$45Lowest knownAll computed
4,096$65.96Lowest known$65.96Lowest knownAll computed
32,768$352.68Lowest known$352.68Lowest knownAll computed
131,072$1,335.72Lowest known$1,335.72Lowest knownAll computed
271,999$2,744.99Lowest known$2,744.99Lowest knownAll computed
272,000$2,745Lowest known$2,745Lowest knownAll computed
272,001$2,745.01Lowest known$5,477.52All computed
Vary output; hold input, requests, cache and retries fixed.
Output tokensClaude Fable 5.1GPT-6 Astra
128$26.4$26.4
2,048$122.4$122.4
8,192$429.6$429.6

Bring your observed evaluation results

JSON is parsed locally. Prompts, filenames, individual responses and extra fields are not retained. Import only aggregate measurements for selected models. Task/version labels do not establish that two evaluations used the same dataset.

Expected format
[{"model":"provider/exact-model-id","task":"support-answer","version":"rubric-1","attempts":100,"successes":84,"costUsd":2.4,"latencyMs":950}]

Use the exact catalogue ID. Replace the example values with observed measurements. Omit costUsd or latencyMs when they are unknown. No public score is inferred from these observations.

Keep the decision and its evidence

A portable record retains selected facts, complete tier ladders, public requirements and the publication manifest. It also embeds the full permitted public catalogue to verify the input artifact checksum. Files are larger for this reason (up to 2 MB); local storage is limited to 12 records. Team review is local to this browser; there is no hosted collaboration.

Saving is opt-in and includes private review fields. Shared comparison links never include them. Version 1 Check references remain separate and are not overwritten or guessed into this format.

Saved local decisions · 0

No version 2 decision records are stored in this browser.

Questions this page answers

Is Claude Fable 5.1 a better-and-cheaper replacement for GPT-6 Astra?

Claude Fable 5.1 has an equal-or-higher measured score and an equal-or-lower estimated price. Switching from GPT-6 Astra loses capability or fails a requirement. Review the migration checks. The reported score intervals do not overlap; this is not a task-specific success guarantee.

What is included in this comparison?

Accepted model capabilities, context and output limits, complete price-tier ladders, independent LMArena measurements and missing evidence. Provider endpoint precision and application success still need verification.

Can I compare a different workload or keep a decision record?

Yes. Change the public workload, prompt length and requirements in the comparison workspace. Fixed-request scenarios, aggregate evaluations and review notes stay local unless explicitly exported.

Evidence & Ask