Model comparison

Claude Fable 5.1 vs Claude Opus 5

Two Anthropic tiers compared on the figures that decide which one a workload actually needs.

Recorded profile verification October 1, 2026Individual provider fields may changeEvidence confidence: Medium — see receipts below

Anthropic

Claude Fable 5.1

Frontier

Anthropic

Claude Opus 5

Frontier

AI model capability comparison
Specification	Claude Fable 5.1	Claude Opus 5
Provider
Provider	Anthropic	Anthropic
Tier
Tier	Frontier	Frontier
Context window
Context window	1M	1M
Max output
Max output	128K	128K
Input / 1M tokens
Input / 1M tokens	$10	Winner: $5
Output / 1M tokens
Output / 1M tokens	$50	Winner: $25
Weights
Weights	Closed	Closed
Parameters
Parameters	Not verifiedUnverified	Not verifiedUnverified
Reasoning levels
Reasoning levels	low, medium, high, xhigh, max	low, medium, high, xhigh, max
Modalities
Modalities	text, image	text, image
API model id
API model id	claude-fable-5-1	claude-opus-5
Released
Released	September 1, 2026	July 24, 2026
Artificial Analysis Intelligence Index [max] · source date Claude Fable 5.1: 2026-10-01
Artificial Analysis Intelligence Index [max] · source date Claude Fable 5.1: 2026-10-01	53	Not verifiedUnverified
Humanity's Last Exam · source date Claude Fable 5.1: 2026-09-01, Claude Opus 5: 2026-09-01 (comparability not verified)
Humanity's Last Exam · source date Claude Fable 5.1: 2026-09-01, Claude Opus 5: 2026-09-01 (comparability not verified)	65	63.6
Terminal-Bench 2.1 · source date Claude Fable 5.1: 2026-09-26
Terminal-Bench 2.1 · source date Claude Fable 5.1: 2026-09-26	91.4	Not verifiedUnverified
Terminal-Bench 2.1 · source date Claude Opus 5: 2026-09-02
Terminal-Bench 2.1 · source date Claude Opus 5: 2026-09-02	Not verifiedUnverified	89.1
DeepSWE 1.1 · source date Claude Fable 5.1: 2026-09-03
DeepSWE 1.1 · source date Claude Fable 5.1: 2026-09-03	67.4	Not verifiedUnverified

Dates beside benchmark scores refer to the linked source’s publication or capture date unless that source explicitly states when it measured the result. A shared URL alone does not establish comparable runs; unverified setups are marked. Prices are USD per million tokens at standard rates, excluding batch and caching discounts. Values we could not confirm from the provider are shown as “Not verified” rather than estimated.

Benchmark receipts

Where each score comes from, and how far it can be compared across models.

Source date2026-10-01
Artificial Analysis (Claude Fable 5.1 (max with fallback))
Composite index blending reasoning, knowledge, and coding evals into one 0–100 score.
Comparable with caveatOnly same-version scores are comparable. v4.3.2 was rebaselined (the top score fell from 66 on v4.1.1 to ~58), so v4.1.1 figures must not be compared with v4.3.2 figures — check the cited source and its date.
Source date2026-09-26
Artificial Analysis Terminal-Bench 2.1 (independent, Terminus 2, max effort)
Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.
Source date2026-09-03
OpenAI GPT-6 Astra launch table quoting a cross-provider result; not a direct Datacurve row (Cross-provider quotation; Fable harness, effort and experiment date unverified)
Agentic software engineering: pass@1 on real repo tasks with reported cost per completed task.
Directly comparable
Source date2026-09-02
Google Gemini 3.8 Flash evaluation table quoting public leaderboard / Artificial Analysis, Terminus 2; not a Google-run Opus evaluation (Cross-provider quotation; common effort and experiment date unverified)
Agentic terminal work: multi-step tasks executed in a sandboxed shell environment.
Comparable with caveatNot comparable with Terminal-Bench 3.0 or 4.0 (different task sets) or v1; harness configuration (container, time limits) also shifts results.
Source date2026-09-01
Anthropic Fable 5.1 comparison table (vendor, with tools; 56.6 no tools)
Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.
Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.
Source date2026-09-01
Anthropic Fable 5.1 announcement (vendor, with tools; 60.9 no tools) — Anthropic's later Opus 5.5 table lists 65.6; conflict preserved
Frontier-knowledge ceiling: extremely hard multi-domain questions written to be near-impossible without deep expertise.
Comparable with caveatSubset/tool configurations (text-only vs with-tools) differ between vendors and materially change scores; must match configuration to compare.

Pricing tiers

Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027.

Claude Opus 5: Standard $5/$25 per MTok with no long-context surcharge. Cache reads $0.50; 5-minute writes $6.25 and 1-hour writes $10. Batch $2.50/$12.50. First-party Fast research preview $10/$50, unavailable with Batch. US-only inference adds 10% where supported. Batch 300K output requires output-300k-2026-03-24; standard stays 128K. Knowledge cutoff May 2026; retirement not sooner than July 24, 2027.

FrontierRecord checked October 1, 2026

Claude Fable 5.1

Claude Fable 5.1 is Anthropic's model for the most demanding reasoning and long-horizon agentic work at $10/$50 — Anthropic now recommends Opus 5.5 as the default for most workloads.

Best for

Frontier agents
Hardest reasoning work
Fable 5 workloads at the same price

Watch out

Standard token rates are 2.5x Opus 5.5's. Forced tool use errors; thinking blocks are model/conversation-bound, so editing earlier turns or switching models can invalidate them. Display updates and per-message effort are beta. Match benchmark settings and evaluate pinned workloads before migrating.

FrontierRecord checked October 1, 2026

Claude Opus 5

Claude Opus 5 is Anthropic's July 2026 agentic-coding model, now 'Active (legacy)'. Its successor Opus 5.5 has lower base input/output prices ($4/$20 vs $5/$25 per million tokens); performance depends on the workload and evaluation settings.

Best for

Complex agentic coding
Enterprise work
Long-context analysis

Watch out

Active legacy, superseded by Opus 5.5. Test migration: Opus 5.5 makes adaptive thinking always on, rejects forced tool use and the older computer-use tool, and changes thinking-block/progress behavior. Partner cloud lifecycles and prices can differ.

When the cheaper one wins

Claude Opus 5 is cheaper on output at $25 per million tokens against $50 for Claude Fable 5.1 — about 2.0×. 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. This compares standard short-context token rates, not total cost per accepted task. Include input, cache, context tiers, schedules, retries and review in your pilot.

Run the model picker

Evidence confidence: Medium

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.
No directly aligned benchmark setup — No benchmark has matching cited sources, source dates, units, effort and recorded run details on both models.
Verified within the last 90 days — Older of the two catalog checks was 25 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 5.1: Claude model overview — whole-profile source check October 1 (accessed 2026-10-01)
Claude Fable 5.1: Claude current API pricing, caching and inference geography (accessed 2026-10-01)
Claude Fable 5.1: Anthropic pricing — Fable 5.1/Mythos 5.1 $10/$50 (accessed 2026-09-03)
Claude Fable 5.1: Anthropic models overview — Fable 5.1 (1M context, 128K output) (accessed 2026-09-03)
Claude Fable 5.1: Anthropic — Claude Fable and Mythos 5.1 announcement (accessed 2026-09-26)
Claude Fable 5.1: Anthropic models overview — Opus 5.5 default; Fable 5.1 for demanding reasoning (accessed 2026-09-26)
Claude Fable 5.1: Anthropic effort documentation (Fable 5.1 selectable effort) (accessed 2026-10-01)
Claude Opus 5: Claude model overview — whole-profile source check October 1 (accessed 2026-10-01)
Claude Opus 5: Claude current API pricing, caching and inference geography (accessed 2026-10-01)
Claude Opus 5: Anthropic — Claude Opus 5 (accessed 2026-08-29)
Claude Opus 5: Anthropic news — Claude Opus 5 (accessed 2026-08-29)
Claude Opus 5: Anthropic — Claude Opus 5.5 (Opus 5 successor) (accessed 2026-09-26)
Claude Opus 5: Anthropic selectable effort levels (separate from adaptive thinking mode) (accessed 2026-10-01)

Related comparisons

Diving deeper on one model? Claude Fable 5.1 · Claude Opus 5

Common questions

Claude Fable 5.1 vs Claude Opus 5

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

Is Claude Fable 5.1 or Claude Opus 5 cheaper for input?

Claude Opus 5 is cheaper at $5 per million input tokens, against $10 for Claude Fable 5.1 — roughly 2.0× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027. Claude Opus 5: Standard $5/$25 per MTok with no long-context surcharge. Cache reads $0.50; 5-minute writes $6.25 and 1-hour writes $10. Batch $2.50/$12.50. First-party Fast research preview $10/$50, unavailable with Batch. US-only inference adds 10% where supported. Batch 300K output requires output-300k-2026-03-24; standard stays 128K. Knowledge cutoff May 2026; retirement not sooner than July 24, 2027.

Is Claude Fable 5.1 or Claude Opus 5 cheaper for output?

Claude Opus 5 is cheaper at $25 per million output tokens, against $50 for Claude Fable 5.1 — roughly 2.0× the price. Estimate both input and output token volume for your workload. These are base rates; Claude Fable 5.1: Standard $10/$50 per MTok with no long-context surcharge. Cache reads $0.25, versus Fable 5's $1; 5-minute writes $12.50 and 1-hour writes $20. Batch $5/$25. US-only inference adds 10% where supported. Adaptive thinking is always on, default effort high; knowledge cutoff Jun 2026. Retirement not sooner than September 1, 2027. Claude Opus 5: Standard $5/$25 per MTok with no long-context surcharge. Cache reads $0.50; 5-minute writes $6.25 and 1-hour writes $10. Batch $2.50/$12.50. First-party Fast research preview $10/$50, unavailable with Batch. US-only inference adds 10% where supported. Batch 300K output requires output-300k-2026-03-24; standard stays 128K. Knowledge cutoff May 2026; retirement not sooner than July 24, 2027.

Which has the larger context window, Claude Fable 5.1 or Claude Opus 5?

Both accept about 1M tokens of context, so document length will not decide between them.

Do Claude Fable 5.1 and Claude Opus 5 support the same reasoning levels?

Both expose these named effort settings: "low", "medium", "high", "xhigh", "max". The same labels do not guarantee equal compute budgets or behavior across providers. Compare quality, latency and cost on your own tasks.

Should I use Claude Fable 5.1 or Claude Opus 5?

Both are classified in our frontier tier; this editorial grouping does not imply equal capability. Claude Fable 5.1 is a candidate for frontier agents; Claude Opus 5 is a candidate for complex agentic coding. Compare accuracy, tool reliability, latency and cost on representative tasks.

Next step

Choosing between them

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

Input price: Claude Opus 5 costs $5 per 1M tokens versus $10 for Claude Fable 5.1 — a 2x difference at the headline tier.

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