Coding
Like-for-like- Claude Fable 5.1
- 81.2
- GPT-5.5
- 58.6
- Weighted basis
- 1 vs 1 rows
- Reading
- Claude Fable 5.1 leads
Claude Fable 5.1 vs GPT-5.5
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 72.68, but the 90% score intervals overlap. Treat that as a lead, not a settled winner.
6 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.
Coding work
Code generation, repair, and software-engineering tasks
Claude Fable 5.1
Claude Fable 5.1 leads on the same 1 weighted benchmark row.
Confidence: limited
Chat turn cost
1K fresh input + 500 output tokens
GPT-5.5
GPT-5.5 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
GPT-5.5
GPT-5.5 has the lower estimated token cost for this stated workload. Costs use the listed standard API rates.
Confidence: listed-rates
Show secondary and unsupported calls
Repository review cost
50K fresh input + 3K output tokens
GPT-5.5
GPT-5.5 has the lower estimated token cost for this stated workload. Costs use the listed standard API rates.
Confidence: listed-rates
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.
12 Claude Fable 5.1 only
6 Shared
27 GPT-5.5 only
- Shared results
- 6
- Claude Fable 5.1 only
- 12
- GPT-5.5 only
- 27
- Like-for-like categories
- 2 / 8
1 category uses 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.
Reasoning
Like-for-like- Claude Fable 5.1
- 90.0
- GPT-5.5
- 85.0
- Weighted basis
- 1 vs 1 rows
- Reading
- Claude Fable 5.1 leads
Knowledge
Directional only- Claude Fable 5.1
- 65.0
- GPT-5.5
- 57.8
- Weighted basis
- 1 vs 2 rows
- Reading
- Directional only
Agentic
Not comparable- Claude Fable 5.1
- Not measured
- GPT-5.5
- 81.6
- Weighted basis
- 0 vs 3 rows
- Reading
- Not comparable
Math
Not comparable- Claude Fable 5.1
- Not measured
- GPT-5.5
- 47.6
- Weighted basis
- 0 vs 2 rows
- Reading
- Not comparable
Multilingual
Not comparable- Claude Fable 5.1
- Not measured
- GPT-5.5
- Not measured
- Weighted basis
- 0 vs 0 rows
- Reading
- Not comparable
Multimodal
Not comparable- Claude Fable 5.1
- Not measured
- GPT-5.5
- 70.4
- Weighted basis
- 0 vs 2 rows
- Reading
- Not comparable
Instruction following
Not comparable- Claude Fable 5.1
- Not measured
- GPT-5.5
- Not measured
- Weighted basis
- 0 vs 0 rows
- Reading
- Not comparable
| Category | Claude Fable 5.1 | GPT-5.5 | Weighted basis | Reading |
|---|---|---|---|---|
| Coding | 81.2 | 58.6 | Like-for-like1 vs 1 rows | Claude Fable 5.1 leads |
| Reasoning | 90.0 | 85.0 | Like-for-like1 vs 1 rows | Claude Fable 5.1 leads |
| Knowledge | 65.0 | 57.8 | Directional only1 vs 2 rows | Directional only |
| Agentic | Not measured | 81.6 | Not comparable0 vs 3 rows | Not comparable |
| Math | Not measured | 47.6 | Not comparable0 vs 2 rows | Not comparable |
| Multilingual | Not measured | Not measured | Not comparable0 vs 0 rows | Not comparable |
| Multimodal | Not measured | 70.4 | 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.
SWE-bench Pro
Coding
HLE
Knowledge
ARC-AGI-2
Reasoning
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
- GPT-5.5
- $0.02
- Fits in one request
GPT-5.5 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
- GPT-5.5
- $0.34
- Fits in one request
GPT-5.5 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
- GPT-5.5
- $0.5
- Fits in one request
GPT-5.5 has the lower modeled cost
Costs use the listed standard API rates.
Specification differences
Sourced differences are shown directly. Missing facts stay explicit instead of being inferred from a model name or family.
SpecificationClaude Fable 5.1GPT-5.5
Context window
Maximum documented context; output-token limits may be lower.
Claude Fable 5.1
GPT-5.5
API model ID
Claude Fable 5.1
claude-fable-5-1
Anthropic Fable 5.1 and Mythos 5.1 launchGPT-5.5
gpt-5.5
OpenAI pricingCached-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 launchGPT-5.5
$0.5 per 1M cached input tokens
OpenAI pricingDocumented inputs
Claude Fable 5.1
Not sourced
GPT-5.5
Not sourced
Documented outputs
Claude Fable 5.1
Not sourced
GPT-5.5
Not sourced
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 launchGPT-5.5
Not sourced
Reasoning profile
Claude Fable 5.1
Reasoning
GPT-5.5
Reasoning
Weight access
Claude Fable 5.1
Proprietary
GPT-5.5
Proprietary
License
Claude Fable 5.1
Proprietary
GPT-5.5
Proprietary
Release date
Claude Fable 5.1
2026-09-01
GPT-5.5
2026-04-23
If you already use one of these models
- Deployment change
- The models list different providers, so authentication, endpoint behavior, limits, and feature support may change.
- Quality signal
- Claude Fable 5.1 has the higher public score estimate, 82.74 versus 72.68, but the 90% score intervals overlap.
- Workload cost
- Repository review: $0.65 vs $0.34. Cache-heavy agent loop: $0.75 vs $0.5.
- 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 evidence45 rows
Agentic
Terminal-Bench 4.0
Claude Fable 5.155.80%SourceGPT-5.5—Not directly comparable
Terminal-Bench-Science 0.1
Claude Fable 5.152.6%SourceGPT-5.5—Not directly comparable
OSWorld 2.0
Claude Fable 5.141.7%SourceGPT-5.513.0%SourceClaude Fable 5.1 leads this result
AutomationBench
Claude Fable 5.131.4%SourceGPT-5.5—Not directly comparable
Toolathlon-Verified
Claude Fable 5.177.8%SourceGPT-5.5—Not directly comparable
Toolathlon Verified Pass@3
Claude Fable 5.181.5%SourceGPT-5.5—Not directly comparable
Toolathlon Verified Pass³
Claude Fable 5.173.1%SourceGPT-5.5—Not directly comparable
Toolathlon Verified avg. turns
Claude Fable 5.123.7 turnsSourceGPT-5.5—Not directly comparable
Terminal-Bench 2.0
Claude Fable 5.1—GPT-5.582%SourceNot directly comparable
CyberGym
Claude Fable 5.1—GPT-5.581.8%SourceNot directly comparable
BrowseComp
Claude Fable 5.1—GPT-5.584.4%SourceNot directly comparable
OSWorld-Verified
Claude Fable 5.1—GPT-5.578.7%SourceNot directly comparable
MCP Atlas
Claude Fable 5.1—GPT-5.575.3%SourceNot directly comparable
Toolathlon
Claude Fable 5.1—GPT-5.555.6%SourceNot directly comparable
τ²-bench results
Claude Fable 5.1—GPT-5.598%SourceNot directly comparable
Gert Labs
Claude Fable 5.1—GPT-5.572.93%SourceNot directly comparable
ResearchClawBench
Claude Fable 5.1—GPT-5.517.0%SourceNot directly comparable
JobBench
Claude Fable 5.1—GPT-5.542.7%SourceNot directly comparable
ExploitGym
Claude Fable 5.1—GPT-5.513.4%SourceNot directly comparable
Coding
SWE-bench Pro
Claude Fable 5.181.2%SourceGPT-5.558.6%SourceClaude Fable 5.1 leads this result
SWE Multilingual
Claude Fable 5.189.1%SourceGPT-5.5—Not directly comparable
SWE Multimodal
Claude Fable 5.154.7%SourceGPT-5.5—Not directly comparable
deepSwe
Claude Fable 5.167.4%SourceGPT-5.5—Not directly comparable
ProgramBench
Claude Fable 5.187.6%SourceGPT-5.5—Not directly comparable
cursorBench32
Shared sourceClaude Fable 5.173.4%GPT-5.558.4%Claude Fable 5.1 leads this result
Terminal-Bench 2.0
Claude Fable 5.1—GPT-5.582.0%SourceNot directly comparable
Vibe Code Bench
Claude Fable 5.1—GPT-5.569.85%SourceNot directly comparable
React Native Evals
Claude Fable 5.1—GPT-5.584.7%SourceNot directly comparable
cursorBench31
Claude Fable 5.1—GPT-5.559.2%SourceNot directly comparable
FrontierCode 1.1 Main
Claude Fable 5.1—GPT-5.543.0%SourceNot directly comparable
Reasoning
ARC-AGI-1
Claude Fable 5.197.50%SourceGPT-5.5—Not directly comparable
ARC-AGI-2
Claude Fable 5.190%SourceGPT-5.585%SourceClaude Fable 5.1 leads this result
MRCR v2 64K-128K
Claude Fable 5.1—GPT-5.583.1%SourceNot directly comparable
MRCR v2 128K-256K
Claude Fable 5.1—GPT-5.587.5%SourceNot directly comparable
ARC-AGI-3
Claude Fable 5.1—GPT-5.50.4%SourceNot directly comparable
Knowledge
HLE
Claude Fable 5.165%SourceGPT-5.552.2%SourceClaude Fable 5.1 leads this result
HLE w/o tools
Claude Fable 5.160.9%SourceGPT-5.541.4%SourceClaude Fable 5.1 leads this result
GPQA
Claude Fable 5.1—GPT-5.593.6%SourceNot directly comparable
GPQA-D
Claude Fable 5.1—GPT-5.593.6%SourceNot directly comparable
Math
Multimodal
Frequently asked questions
Which is better, Claude Fable 5.1 or GPT-5.5?
Claude Fable 5.1 has the higher public score estimate, 82.74 versus 72.68, 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 GPT-5.5?
Claude Fable 5.1 leads the like-for-like coding comparison across 1 shared weighted benchmark row.
Which is better for agentic tasks, Claude Fable 5.1 or GPT-5.5?
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 GPT-5.5?
For the stated presets, chat costs $0.035 on Claude Fable 5.1 and $0.02 on GPT-5.5; repository review costs $0.65 and $0.34; the cache-heavy agent loop costs $0.75 and $0.5. Costs use the listed standard API rates.
Which has the larger context window, Claude Fable 5.1 or GPT-5.5?
Both models list the same context window, 1M.
Related comparisons
Last updated September 1, 2026
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