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Claude Fable 5.1 vs Claude Sonnet 5.5
Of the 6 public leaderboards that rate both, Claude Fable 5.1 scores higher on 2 and Claude Sonnet 5.5 on 4. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, Claude Fable 5.1 is at 93.4 and Claude Sonnet 5.5 at 90.3 (out of 100).
Scores as published by each board; table composed October 8, 2026.
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Leaderboard by leaderboard
| Board | Claude Fable 5.1 | Claude Sonnet 5.5 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,743.7 | 1,774.3 | Claude Sonnet 5.5 |
| LiveBench global average (0-100) | 83.4 | 77.8 | Claude Fable 5.1 |
| SimpleBench AVG@5 % (private set) | 86.6 | 75.9 | Claude Fable 5.1 |
| LLM Stats LLM Stats Score · composite (0-100), their rendered top 15 | 53.5 | 58.3 | Claude Sonnet 5.5 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 65.8 | 67 | Claude Sonnet 5.5 |
| Artificial Analysis intelligence index · measured runs only | 53.4 | 56 | Claude Sonnet 5.5 |
Raw scores are each board's own scale, so compare within a row, not across rows. Full table: the bench index.
For coding
On the ArtificialWatch coding index, Claude Fable 5.1 is at 88.2 (#3 of 35) and Claude Sonnet 5.5 at 88.2 (#3). Claude Fable 5.1 scores higher on 2 of the 3 coding boards that rate both and Claude Sonnet 5.5 on 1.
| Coding board | Claude Fable 5.1 | Claude Sonnet 5.5 |
|---|---|---|
| LMArena · Coding | 1,534 | 1,531.8 |
| LiveBench · Coding | 76.2 | 73.8 |
| Vals Vibe Code Bench | 90.3 | 92.4 |
Claude Fable 5.1 at a glance
- Developer
- Anthropic
- Status
- Live since September 1, 2026
- API price
- $10 input / $50 output per 1M tokens · Anthropic, claude-fable-5-1
- Context window
- 1M tokens
Live - sticker price held at $10/$50, but cache reads cut 75% to $0.25 = ~25% cheaper typical, up to ~45% agentic · 1M ctx · effort low-max.
Claude Fable 5.1 is live — the sticker price never moved, and the cache read fell 75%
2026-09-01 · Claude Fable 5.1 shipped today, alongside Claude Mythos 5.1. Our radar detected it at 17:52:22 UTC and confirmed it on the next sweep 60 seconds later.
Fable 5.1's August window has closed — the market now prices September at 78%, and one claim in the leak can't be checked at all
2026-08-20 · A claim going round today says Fable 5.1 is in pre-release testing, targeted at September, and running inside Anthropic's own products under the Fable 5 name. One part of that is checkable, one part is checkable and slipping, and one part is — by construction — invisible to anything we can measure.
Claude Sonnet 5.5 at a glance
- Developer
- Anthropic
- Status
- Live since September 28, 2026
- API price
- $2 input / $10 output per 1M tokens · Anthropic, claude-sonnet-5-5
- Context window
- 1M tokens
Live — Sep 28 · $2/$10 per MTok, the same as Sonnet 5 · cache reads $0.20 at launch, halved to $0.10 on Oct 7, writes $2.50 · in the API, the Claude apps, AWS, Google Cloud and Azure the same day · 1M ctx / 128K out · knowledge cutoff Jun 2026 · Artificial Analysis Intelligence Index 56 at max effort, #3 of 216 reasoning models (read Sep 28) · Anthropic's own table: Terminal-Bench 4.0 70.6% (Opus 5.5 66.4%), OSWorld 2.1 80.1% (Opus 5.5 81.8%) · our sweep caught claude-sonnet-5-5 at 17:54 UTC and fired at 17:55.
Claude Sonnet 5.5 ships at Sonnet 5's price, and the first independent number puts it #3 among reasoning models
2026-09-28 · Claude Sonnet 5.5 is live. Our sweep read the id claude-sonnet-5-5 at 17:54:45 UTC on September 28 and the alert went out at 17:55:45, 60 seconds later, to 314 inboxes and one phone. OpenRouter listed it nine minutes after that.
Claude Sonnet 5.5: named by Anthropic, reportedly in partner testing, priced 89% by Sep 30
2026-09-27 · Anthropic has named Claude Sonnet 5.5 but has not dated it. Everything past the name is reported, not confirmed - and the one number that moves every day says it is close.
Claude Fable 5.1 vs Claude Sonnet 5.5: quick answers
Which is better, Claude Fable 5.1 or Claude Sonnet 5.5?
It depends on what you measure. Of the 6 public leaderboards that rate both, Claude Fable 5.1 scores higher on 2 and Claude Sonnet 5.5 on 4. Claude Fable 5.1's widest lead is on LiveBench; Claude Sonnet 5.5's widest lead is on LLM Stats. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, Claude Fable 5.1 is at 93.4 and Claude Sonnet 5.5 at 90.3 (out of 100).
Which is newer, Claude Fable 5.1 or Claude Sonnet 5.5?
Claude Sonnet 5.5. It went live on September 28, 2026, 27 days after Claude Fable 5.1 (September 1, 2026).
Which is cheaper, Claude Fable 5.1 or Claude Sonnet 5.5?
Claude Sonnet 5.5 is cheaper on both input and output. On each vendor's own API, Claude Fable 5.1 is $10 input / $50 output per million tokens and Claude Sonnet 5.5 is $2 input / $10 output per million tokens. Prices as published in the models.dev catalog, as of 2026-10-08.
Which has the bigger context window, Claude Fable 5.1 or Claude Sonnet 5.5?
Neither. Both take 1M tokens.
How do Claude Fable 5.1 and Claude Sonnet 5.5 compare for coding?
On the ArtificialWatch coding index, Claude Fable 5.1 is at 88.2 (#3 of 35) and Claude Sonnet 5.5 at 88.2 (#3). Claude Fable 5.1 scores higher on 2 of the 3 coding boards that rate both and Claude Sonnet 5.5 on 1.
Who makes Claude Fable 5.1 and Claude Sonnet 5.5?
Both are from Anthropic.
Where do these numbers come from?
Each score is the leaderboard's own published figure, read by ArtificialWatch (table composed October 8, 2026). Boards measure different things, so raw scores are only comparable within a row.
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