Reasoning
Like-for-like- Claude Fable 5.1
- 90.0
- Claude Opus 4.8
- 72.1
- Weighted basis
- 1 vs 1 rows
- Reading
- Claude Fable 5.1 leads
Claude Fable 5.1 vs Claude Opus 4.8
Updated September 1, 2026. Public scores include evidence status and uncertainty. They are not guarantees for a specific workload.
Decision reading
Claude Fable 5.1 has the higher public score estimate, 82.74 versus 75.96, but the 90% score intervals overlap. Treat that as a lead, not a settled winner.
8 results are shared. Category rows based on different benchmark sets are marked directional and do not name a winner.
Which one for your work
Recommendations appear only when a shared evidence basis or an explicit operating constraint supports the call. Secondary and unsupported use cases stay disclosed below the initial list.
Chat turn cost
1K fresh input + 500 output tokens
Claude Opus 4.8
Claude Opus 4.8 has the lower estimated token cost for this stated workload. Costs use the listed standard API rates.
Confidence: listed-rates
Cache-heavy agent loop cost
200K cached + 20K fresh input + 10K output tokens
Claude Fable 5.1
Claude Fable 5.1 has the lower estimated token cost for this stated workload. Claude Opus 4.8 has no published cached-input rate, so cached tokens use its listed input rate.
Confidence: rate-fallback
Show secondary and unsupported calls
Repository review cost
50K fresh input + 3K output tokens
Claude Opus 4.8
Claude Opus 4.8 has the lower estimated token cost for this stated workload. Costs use the listed standard API rates.
Confidence: listed-rates
Coding work
Code generation, repair, and software-engineering tasks
Not enough matched evidence
The category averages use different weighted benchmark sets, so they are directional rather than like-for-like.
Confidence: limited
Agentic work
Tool use, computer use, and multi-step task completion
Not enough matched evidence
No shared weighted benchmark basis supports a winner.
Confidence: limited
Long documents
Prompts that approach the documented context limit
No clear pick
The documented context windows are equal.
Confidence: documented
What is actually comparable
Shared results can support a head-to-head reading. Results present for only one model describe coverage, not superiority.
10 Claude Fable 5.1 only
8 Shared
25 Claude Opus 4.8 only
- Shared results
- 8
- Claude Fable 5.1 only
- 10
- Claude Opus 4.8 only
- 25
- Like-for-like categories
- 1 / 8
2 categories use different evidence sets. Those rows remain visible for coverage context but do not name a winner.
Category results, on a stated basis
Each row states whether both averages use the same weighted benchmark set. Directional and not-comparable rows remain visible, but they never receive a winner in this template.
Coding
Directional only- Claude Fable 5.1
- 81.2
- Claude Opus 4.8
- 81.1
- Weighted basis
- 1 vs 2 rows
- Reading
- Directional only
Knowledge
Directional only- Claude Fable 5.1
- 65.0
- Claude Opus 4.8
- 62.7
- Weighted basis
- 1 vs 2 rows
- Reading
- Directional only
Agentic
Not comparable- Claude Fable 5.1
- Not measured
- Claude Opus 4.8
- 80.3
- Weighted basis
- 0 vs 3 rows
- Reading
- Not comparable
Math
Not comparable- Claude Fable 5.1
- Not measured
- Claude Opus 4.8
- 53.9
- Weighted basis
- 0 vs 3 rows
- Reading
- Not comparable
Multilingual
Not comparable- Claude Fable 5.1
- Not measured
- Claude Opus 4.8
- Not measured
- Weighted basis
- 0 vs 0 rows
- Reading
- Not comparable
Multimodal
Not comparable- Claude Fable 5.1
- Not measured
- Claude Opus 4.8
- 77.0
- Weighted basis
- 0 vs 2 rows
- Reading
- Not comparable
Instruction following
Not comparable- Claude Fable 5.1
- Not measured
- Claude Opus 4.8
- Not measured
- Weighted basis
- 0 vs 0 rows
- Reading
- Not comparable
| Category | Claude Fable 5.1 | Claude Opus 4.8 | Weighted basis | Reading |
|---|---|---|---|---|
| Reasoning | 90.0 | 72.1 | Like-for-like1 vs 1 rows | Claude Fable 5.1 leads |
| Coding | 81.2 | 81.1 | Directional only1 vs 2 rows | Directional only |
| Knowledge | 65.0 | 62.7 | Directional only1 vs 2 rows | Directional only |
| Agentic | Not measured | 80.3 | Not comparable0 vs 3 rows | Not comparable |
| Math | Not measured | 53.9 | Not comparable0 vs 3 rows | Not comparable |
| Multilingual | Not measured | Not measured | Not comparable0 vs 0 rows | Not comparable |
| Multimodal | Not measured | 77.0 | Not comparable0 vs 2 rows | Not comparable |
| Instruction following | Not measured | Not measured | Not comparable0 vs 0 rows | Not comparable |
Shape of the matched evidence
Only shared public evidence is shown. Sparse evidence stays a ruled list rather than being closed into a radar shape.
Too few matched category axes support a radar. The ruled list below shows only shared benchmark results; positions use each benchmark’s normalized display scale when available.
ARC-AGI-2
Reasoning
Claude Fable 5.1: 90%Claude Opus 4.8: 72.1%Normalized gap 17.9Claude Fable 5.1 source Claude Opus 4.8 sourceSWE-bench Pro
Coding
Claude Fable 5.1: 81.2%Claude Opus 4.8: 69.2%Normalized gap 12.0Claude Fable 5.1 source Claude Opus 4.8 sourceHLE
Knowledge
Claude Fable 5.1: 65%Claude Opus 4.8: 57.9%Normalized gap 7.1Claude Fable 5.1 source Claude Opus 4.8 source
What each workload costs
Three fixed token mixes turn per-token rates into comparable decisions. Each scenario states context fit and whether cached input had to fall back to the published list-input rate.
Chat turn
1K fresh input + 500 output tokens
- Claude Fable 5.1
- $0.035
- Fits in one request
- Claude Opus 4.8
- $0.0175
- Fits in one request
Claude Opus 4.8 has the lower modeled cost
Costs use the listed standard API rates.
Repository review
50K fresh input + 3K output tokens
- Claude Fable 5.1
- $0.65
- Fits in one request
- Claude Opus 4.8
- $0.325
- Fits in one request
Claude Opus 4.8 has the lower modeled cost
Costs use the listed standard API rates.
Cache-heavy agent loop
200K cached + 20K fresh input + 10K output tokens
- Claude Fable 5.1
- $0.75
- Fits in one request
- Claude Opus 4.8
- $1.35
- Fits in one request
- Cached input priced at the published list-input rate
Claude Fable 5.1 has the lower modeled cost
Claude Opus 4.8 has no published cached-input rate, so cached tokens use its listed input rate.
Specification differences
Sourced differences are shown directly. Missing facts stay explicit instead of being inferred from a model name or family.
SpecificationClaude Fable 5.1Claude Opus 4.8
Context window
Maximum documented context; output-token limits may be lower.
Claude Fable 5.1
Claude Opus 4.8
API model ID
Claude Fable 5.1
claude-fable-5-1
Anthropic Fable 5.1 and Mythos 5.1 launchClaude Opus 4.8
claude-opus-4-8
Anthropic model overviewCached-input rate
A missing cached-input rate falls back to the listed input rate only in the stated workload estimate.
Claude Fable 5.1
$0.25 per 1M cached input tokens
Anthropic Fable 5.1 launchClaude Opus 4.8
Not published
Documented inputs
Claude Fable 5.1
Not sourced
Claude Opus 4.8
text, image
Anthropic model overviewDocumented outputs
Claude Fable 5.1
Not sourced
Claude Opus 4.8
Provider availability
Claude Fable 5.1
Generally Available · Claude API, Claude products, AWS, Google Cloud, Microsoft Azure
Anthropic Fable 5.1 and Mythos 5.1 launchClaude Opus 4.8
Generally Available · Claude API
Anthropic model overviewReasoning profile
Claude Fable 5.1
Reasoning
Claude Opus 4.8
Reasoning
Weight access
Claude Fable 5.1
Proprietary
Claude Opus 4.8
Proprietary
License
Claude Fable 5.1
Proprietary
Claude Opus 4.8
Proprietary
Release date
Claude Fable 5.1
2026-09-01
Claude Opus 4.8
2026-05-28
If you already use one of these models
- Deployment change
- Both entries list Anthropic as the provider. Confirm endpoint, model ID, limits, and feature support before switching.
- Quality signal
- Claude Fable 5.1 has the higher public score estimate, 82.74 versus 75.96, but the 90% score intervals overlap.
- Workload cost
- Repository review: $0.65 vs $0.325. Cache-heavy agent loop: $0.75 vs $1.35.
- Context tradeoff
- Both models list 1M.
Run the same representative tasks against both endpoints before changing production traffic.
Benchmark evidence
The full public result ledger is available for audit without forcing a wide desktop table onto a phone.
Browse raw public benchmark evidence43 rows
Agentic
Terminal-Bench 4.0
Claude Fable 5.155.80%SourceClaude Opus 4.8—Not directly comparable
Terminal-Bench-Science 0.1
Claude Fable 5.152.6%SourceClaude Opus 4.8—Not directly comparable
OSWorld 2.0
Claude Fable 5.141.7%SourceClaude Opus 4.820.6%SourceClaude Fable 5.1 leads this result
AutomationBench
Claude Fable 5.131.4%SourceClaude Opus 4.8—Not directly comparable
Toolathlon-Verified
Claude Fable 5.177.8%SourceClaude Opus 4.8—Not directly comparable
Toolathlon Verified Pass@3
Claude Fable 5.181.5%SourceClaude Opus 4.8—Not directly comparable
Toolathlon Verified Pass³
Claude Fable 5.173.1%SourceClaude Opus 4.8—Not directly comparable
Toolathlon Verified avg. turns
Claude Fable 5.123.7 turnsSourceClaude Opus 4.8—Not directly comparable
Terminal-Bench 3.0
Claude Fable 5.1—Claude Opus 4.821.1%SourceNot directly comparable
Terminal-Bench 2.0
Claude Fable 5.1—Claude Opus 4.874.6%SourceNot directly comparable
BrowseComp
Claude Fable 5.1—Claude Opus 4.884.3%SourceNot directly comparable
DeepSearchQA
Claude Fable 5.1—Claude Opus 4.893.1%SourceNot directly comparable
OSWorld-Verified
Claude Fable 5.1—Claude Opus 4.883.4%SourceNot directly comparable
Finance Agent v2
Claude Fable 5.1—Claude Opus 4.853.9%SourceNot directly comparable
MCP Atlas
Claude Fable 5.1—Claude Opus 4.882.2%SourceNot directly comparable
Toolathlon
Claude Fable 5.1—Claude Opus 4.859.9%SourceNot directly comparable
Gert Labs
Claude Fable 5.1—Claude Opus 4.872.97%SourceNot directly comparable
ResearchClawBench
Claude Fable 5.1—Claude Opus 4.821.1%SourceNot directly comparable
Coding
SWE-bench Pro
Claude Fable 5.181.2%SourceClaude Opus 4.869.2%SourceClaude Fable 5.1 leads this result
SWE Multilingual
Claude Fable 5.189.1%SourceClaude Opus 4.884.4%SourceClaude Fable 5.1 leads this result
SWE Multimodal
Claude Fable 5.154.7%SourceClaude Opus 4.838.4%SourceClaude Fable 5.1 leads this result
deepSwe
Claude Fable 5.167.4%SourceClaude Opus 4.8—Not directly comparable
ProgramBench
Claude Fable 5.187.6%SourceClaude Opus 4.8—Not directly comparable
cursorBench32
Shared sourceClaude Fable 5.173.4%Claude Opus 4.862.3%Claude Fable 5.1 leads this result
SWE-bench Verified
Claude Fable 5.1—Claude Opus 4.888.6%SourceNot directly comparable
Terminal-Bench 2.0
Claude Fable 5.1—Claude Opus 4.874.6%SourceNot directly comparable
cursorBench31
Claude Fable 5.1—Claude Opus 4.858.4%SourceNot directly comparable
FrontierCode 1.1 Main
Claude Fable 5.1—Claude Opus 4.846.5%SourceNot directly comparable
Reasoning
Knowledge
HLE
Claude Fable 5.165%SourceClaude Opus 4.857.9%SourceClaude Fable 5.1 leads this result
HLE w/o tools
Claude Fable 5.160.9%SourceClaude Opus 4.849.8%SourceClaude Fable 5.1 leads this result
GPQA
Claude Fable 5.1—Claude Opus 4.893.6%SourceNot directly comparable
GPQA-D
Claude Fable 5.1—Claude Opus 4.893.6%SourceNot directly comparable
Math
Multilingual
INCLUDE
Claude Fable 5.1—Claude Opus 4.887.6%SourceNot directly comparable
Multimodal
OfficeQA Pro
Claude Fable 5.1—Claude Opus 4.866.2%SourceNot directly comparable
ScreenSpot Pro
Claude Fable 5.1—Claude Opus 4.887.9%SourceNot directly comparable
CharXiv
Claude Fable 5.1—Claude Opus 4.889.9%SourceNot directly comparable
CharXiv w/o tools
Claude Fable 5.1—Claude Opus 4.880.5%SourceNot directly comparable
Frequently asked questions
Which is better, Claude Fable 5.1 or Claude Opus 4.8?
Claude Fable 5.1 has the higher public score estimate, 82.74 versus 75.96, but the 90% score intervals overlap. The higher estimate is not a decisive winner because the uncertainty ranges overlap.
Which is better for coding, Claude Fable 5.1 or Claude Opus 4.8?
The current coding averages use different weighted benchmark sets, so BenchLM does not name a winner from them. Read the shared benchmark rows directly and test the models on the same task set.
Which is better for agentic tasks, Claude Fable 5.1 or Claude Opus 4.8?
The published evidence does not provide a shared weighted agentic tasks basis for both models, so BenchLM does not name a agentic tasks winner.
Which costs less, Claude Fable 5.1 or Claude Opus 4.8?
For the stated presets, chat costs $0.035 on Claude Fable 5.1 and $0.0175 on Claude Opus 4.8; repository review costs $0.65 and $0.325; the cache-heavy agent loop costs $0.75 and $1.35. Claude Opus 4.8 has no published cached-input rate, so cached tokens use its listed input rate.
Which has the larger context window, Claude Fable 5.1 or Claude Opus 4.8?
Both models list the same context window, 1M.
Related comparisons
Last updated September 1, 2026
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