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Claude Fable 5.1 vs Claude Opus 4.8
Claude Fable 5.1 scores higher than Claude Opus 4.8 on all 5 public leaderboards that rate both. 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 95 and Claude Opus 4.8 at 47.8 (out of 100).
Scores as published by each board; table composed September 24, 2026.
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Leaderboard by leaderboard
| Board | Claude Fable 5.1 | Claude Opus 4.8 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,754.7 | 1,555.2 | Claude Fable 5.1 |
| LiveBench global average (0-100) | 83.4 | 76.2 | Claude Fable 5.1 |
| SimpleBench AVG@5 % (private set) | 86.6 | 64.8 | Claude Fable 5.1 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 68.8 | 60.9 | Claude Fable 5.1 |
| Artificial Analysis intelligence index · measured runs only | 53.4 | 41.8 | Claude Fable 5.1 |
Raw scores are each board's own scale, so compare within a row, not across rows. Full table: the bench index.
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 Opus 4.8 at a glance
- Developer
- Anthropic
- Status
- Live since May 27, 2026
- API price
- $5 input / $25 output per 1M tokens · Anthropic, claude-opus-4-8
- Context window
- 1M tokens
Live.
Claude Fable 5.1 vs Claude Opus 4.8: quick answers
Which is better, Claude Fable 5.1 or Claude Opus 4.8?
It depends on what you measure. Claude Fable 5.1 scores higher than Claude Opus 4.8 on all 5 public leaderboards that rate both. Claude Fable 5.1's widest lead is on LiveBench. 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 95 and Claude Opus 4.8 at 47.8 (out of 100).
Which is newer, Claude Fable 5.1 or Claude Opus 4.8?
Claude Fable 5.1. It went live on September 1, 2026, 97 days after Claude Opus 4.8 (May 27, 2026).
Which is cheaper, Claude Fable 5.1 or Claude Opus 4.8?
Claude Opus 4.8 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 Opus 4.8 is $5 input / $25 output per million tokens. Prices as published in the models.dev catalog, as of 2026-09-24.
Which has the bigger context window, Claude Fable 5.1 or Claude Opus 4.8?
Neither. Both take 1M tokens.
Who makes Claude Fable 5.1 and Claude Opus 4.8?
Both are from Anthropic.
Where do these numbers come from?
Each score is the leaderboard's own published figure, read by ArtificialWatch (table composed September 24, 2026). Boards measure different things, so raw scores are only comparable within a row.
More comparisons
Watch free: Chrome push the moment a new model answers on a public API, an email about 15 minutes later. Also: the bench index · API pricing · the wire