Roboflow
Anthropic

Anthropic: Claude Fable 5.1

Claude Fable 5.1 Overview

Claude Fable 5.1 is a proprietary multimodal model from Anthropic in the Mythos-class tier of the Claude 5 family, positioned above Claude Opus for demanding reasoning and long-horizon agentic work. It accepts text and images as input and returns text, with a one million token context window and a maximum output of 128 thousand tokens. Adaptive thinking is always on, and an effort parameter controls how much reasoning the model applies to a given request. Anthropic reports a reliable knowledge and training data cutoff of June 2026. Claude Fable 5.1 and Claude Mythos 5.1 share the same underlying model; the difference between them is the set of safety classifiers applied to dual-use cybersecurity and biology requests.

On the vision side, Anthropic documents improvements in reading dense charts, financial filings, and tables nested inside PDF documents, which extends the model toward document understanding, chart question answering, and spreadsheet and slide work. Reported evaluations cover agentic scientific research on Terminal-Bench-Science 0.1, agentic coding on Terminal-Bench 4.0, computer use on OSWorld 2.0, and multidisciplinary reasoning on Humanity's Last Exam. Model weights are not published.

Claude Fable 5.1 Interactive Demo

Model settings

Extended thinking

Max output tokens

Default 65,536 · max 65,536

Sign in to adjust thinking and output length per run.

Results appear here. Add an image or pick an example to run Claude Fable 5.1.

Claude Fable 5.1 Details & Performance

Details

Resources

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Vision Tasks

CaptioningChart Question AnsweringClassificationDocument Question AnsweringImage TaggingMulti-Label ClassificationOCRObject DetectionVision LanguageVisual Question Answering

Features

Foundation VisionLLMs with Vision CapabilitiesMultimodal Vision

Usage

Past 30 Days

Performance

Avg. Latency

Claude Fable 5.1 Vision Evals

Vision Evals is Roboflow's ground-truth benchmark: every model runs the same real-world samples across five vision tasks, and answers are scored against ground truth.

Evals updated October 13, 2026Pricing updated October 17, 2026

Overall score#14 of 63
74.7%
Avg cost / sample#62 of 63
$0.039
Avg speed / sample#18 of 63
8.35s
Avg tokens / sample
2.5K

Strengths and weaknesses

Claude Fable 5.1 averages 74.7% across the five Vision Evals tasks, ranking #14 of 63 models overall.

Its weakest relative showing is Counting, ranking #20 of 63 at 69.4%.

At $0.039 per sample it is the 62nd cheapest of the 63 benchmarked models, and its average inference time of 8.3s per sample makes it the 18th fastest.

Performance profile

Field medianClaude Fable 5.1

Field medians: Object Detection 54.4%, Counting 63.5%, Identification 84.4%, OCR 63.6%, Reasoning 57.6%.

Results by task

TaskScoreField (0 to 100)RankCost / sampleSpeed
Object Detection (low)
61.4%
±0.5, Mean of 3 runs, range 61.0 to 62.0
#17 of 63$0.06011.98s
Object Detection (high)
65.0%
±0.4, Mean of 3 runs, range 64.6 to 65.3
#18 of 31$0.07817.13s
Counting (low)
69.4%
±2.7, Mean of 3 runs, range 66.2 to 71.6
#20 of 63$0.0195.75s
Counting (high)
73.0%
±4.7, Mean of 3 runs, range 67.6 to 77.0
#17 of 31$0.0236.53s
Identification (low)
97.9%
±1.6, Mean of 3 runs, range 96.9 to 100.0
#5 of 63$0.0135.01s
Identification (high)
96.9%
±3.1, Mean of 3 runs, range 93.8 to 100.0
#3 of 31$0.0144.95s
OCR (low)
72.9%
#9 of 47$0.0397.94s
Single value
64.3%
Transcription
84.7%
Structured JSON
89.2%
Text localization
46.5%
OCR (high)
75.3%
#10 of 47$0.05110.22s
Single value
69.1%
Transcription
95.2%
Structured JSON
89.5%
Text localization
43.4%
Reasoning (low)
72.0%
±1.3, Mean of 3 runs, range 70.9 to 73.5
#17 of 63$0.0195.94s
Reasoning (high)
73.1%
±2.0, Mean of 3 runs, range 71.5 to 75.5
#20 of 50$0.0288.05s
  • Thinking longer helps: 3.6 points higher on object detection at high effort for 1.3x the cost and 1.4x the latency.
  • Thinking longer helps: 3.6 points higher on counting at high effort for 1.2x the cost and 1.1x the latency.
  • Thinking longer does not help: 1 points lower on identification at high effort for 1.1x the cost and 1x the latency.
  • Thinking longer helps: 2.4 points higher on ocr at high effort for 1.3x the cost and 1.3x the latency.
  • Thinking longer helps: 1.1 points higher on reasoning at high effort for 1.5x the cost and 1.4x the latency.

Price vs. performance

Score vs. cost

Overall benchmark score against estimated cost per sample, on a log scale. Upper-left is the sweet spot: high quality at low cost.

62 models on the current benchmark · scores and efficiency pooled across all five tasks at low effort · Claude Fable 5.1 highlighted

Claude Fable 5.1 scores are the mean of 3 runs per task at both low and high effort; OCR is a single preliminary run · Methodology

View all Vision Evals →

Claude Fable 5.1 Pricing

Claude Fable 5.1 costs $10.00 per 1M input tokens and $50.00 per 1M output tokens.

Input$10.00 / 1M tokens
Output$50.00 / 1M tokens
Cached input$0.250 / 1M tokens

Pricing updated Oct 17, 2026

Alternatives to Claude Fable 5.1

Other models worth comparing for similar use cases.

Anthropic
Claude Opus 5.5
Claude Opus 5.5 is a proprietary multimodal reasoning model from Anthropic and the first entry in the Claude 5.5 family. It accepts interleaved text and image input and returns text, with a one million token context window and up to 128,000 output tokens per response. Adaptive thinking is always enabled on this model and cannot be disabled; thinking depth is instead governed by an effort parameter with five levels, where medium is the default, a change from the high default used by Claude Opus 5 and earlier Opus models. Anthropic reports a knowledge cutoff of June 2026.On the visual side, Anthropic characterizes Opus 5.5 as its strongest Opus release for vision and computer use, describing improved reading of dense documents, charts, screenshots, and diagrams for document extraction and visual analysis tasks. Published results include 89.0% on Chartography with tools and 81.8% on OSWorld 2.0 under partial credit scoring, alongside 48.7% under strict scoring reported in the system card. The accompanying system card states that Opus 5.5 scored higher than Opus 5 on every evaluation in its capability summary, with the largest gains concentrated in agentic coding, visual reasoning, computer use, and long-horizon knowledge work. The model ships with safety classifiers covering biology and cybersecurity that can route blocked requests to earlier Claude models.
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Google
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Other Anthropic Fable models

Other versions in the same family as Claude Fable 5.1.

Claude Fable 5.1 License

Proprietary

Claude Fable 5.1 is proprietary: the weights are not distributed, and the Claude Fable 5.1 license is the vendor's commercial terms of service that you accept when you call the API.

Commercial use
Permitted under the vendor terms, typically metered per token or per request, with the vendor usage policy applying to your inputs and outputs.
Modification
Not available. Claude Fable 5.1 weights are closed, so you can configure prompts and use vendor-hosted fine-tuning where it is offered, but you cannot modify the model itself.
Redistribution
Not permitted. You cannot self-host or resell the model; you build on the hosted API instead.

Vendor terms govern data retention, whether your inputs can be trained on, rate limits, and regional availability, and they can change with notice. Review them if you handle regulated or customer data.

Do I need a commercial license for Claude Fable 5.1?

Proprietary terms are set by the vendor rather than negotiated per project, and no open-source obligation attaches to your code. If you would rather deploy an open model instead of Claude Fable 5.1, Roboflow's licensing page lists the models whose commercial license is included when you deploy on Roboflow.

Do not hesitate to reach out with questions for your commercial project — our team will help you start solving business problems on the first call. See Roboflow commercial licensing for the models included in each plan.

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Frequently Asked Questions About Claude Fable 5.1 Vision

Yes. Claude Fable 5.1 accepts image input and handles OCR, object counting, identification, visual reasoning, and object detection. On Roboflow's Vision Evals its strongest task is Identification at 97.9% (#5 of 63 at low effort). You can test it on your own image in the demo above.

Yes, and it is one of the model's strongest vision skills: it scores 72.9% (#9 of 47 at low effort) on Vision Evals OCR, which covers single readings, full transcriptions, structured JSON, and locating text with boxes. Within that, full transcriptions score 84.7%, and returning the fields of a label or form as JSON scores 89.2%.

It's serviceable. On Vision Evals, Claude Fable 5.1 scores 61.4% mAP@50 on object detection (#17 of 63 at low effort) and 69.4% judge-graded accuracy on object counting.

On our benchmark's task mix, Claude Fable 5.1 averages $0.04 per sample at $10.00 per 1M input and $50.00 per 1M output tokens (#62 of 63 on cost), with an average speed of 8.3s per sample across the benchmark. Actual cost depends on your images and prompts.

On the overall Vision Evals ranking, Claude Fable 5.1 sits #14 of 63 at 74.7%, just behind Gemini 3.1 Pro (76.8%) and just ahead of Muse Spark 1.1 (74.4%). See the full side-by-side: Claude Fable 5.1 vs Gemini 3.1 Pro.