← comparisons · head to head
Claude Opus 5.5 vs Claude Fable 5.1
Of the 6 public leaderboards that rate both, Claude Opus 5.5 scores higher on 5 and Claude Fable 5.1 on 1. On the ArtificialWatch Index, which takes the median of each model's percentile across the boards that score it, Claude Opus 5.5 is at 100 and Claude Fable 5.1 at 93.4 (out of 100).
Scores as published by each board; table composed October 8, 2026.
Get the next launch alert, free →
Leaderboard by leaderboard
| Board | Claude Opus 5.5 | Claude Fable 5.1 | Higher |
|---|---|---|---|
| LMArena Elo (community votes) | 1,813 | 1,743.7 | Claude Opus 5.5 |
| LiveBench global average (0-100) | 83.2 | 83.4 | Claude Fable 5.1 |
| SimpleBench AVG@5 % (private set) | 88.4 | 86.6 | Claude Opus 5.5 |
| LLM Stats LLM Stats Score · composite (0-100), their rendered top 15 | 60.4 | 53.5 | Claude Opus 5.5 |
| Vals AI Vals Index accuracy % · weighted finance + coding tasks | 67 | 65.8 | Claude Opus 5.5 |
| Artificial Analysis intelligence index · measured runs only | 57.6 | 53.4 | Claude Opus 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 Opus 5.5 is at 96.9 (#1 of 35) and Claude Fable 5.1 at 88.2 (#3). Claude Opus 5.5 scores higher on all 3 coding boards that rate both.
| Coding board | Claude Opus 5.5 | Claude Fable 5.1 |
|---|---|---|
| LMArena · Coding | 1,549.5 | 1,534 |
| LiveBench · Coding | 80.5 | 76.2 |
| Vals Vibe Code Bench | 90.3 | 90.3 |
Claude Opus 5.5 at a glance
- Developer
- Anthropic
- Status
- Live since September 22, 2026
- API price
- $4 input / $20 output per 1M tokens · Anthropic, claude-opus-5-5
- Context window
- 1M tokens
Live — Sep 22 · $4/$20 per MTok, down from Opus 5 at $5/$25 · 1M ctx / 128K out · adaptive thinking always on, default effort medium · cache reads 5% of base input · Anthropic now says start here for most workloads, and Opus 5 is legacy.
Claude Opus 5.5 ships at $4/$20 - and that is LESS than the Opus 5 it replaces
2026-09-22 · Claude Opus 5.5 is live. Our sweep read the id claude-opus-5-5 at 16:24:44 UTC on September 22 and the alert went out at 16:25:45 - 61 seconds later, to 307 inboxes and one phone. The hunt that caught it was armed the previous day, before the model had a confirmed name, on the version range rather than on the rumour.
Markets put the next Claude Opus at 83% by Thursday — the name going around is 5.5
2026-09-21 · Polymarket's "Next Claude Opus released by...?" book, read directly at 06:49 UTC, September 21: 83% by September 24, 91% by September 27, 95% by September 30. Polymarket's own post about nine hours earlier had Thursday at 72%, so the number has been climbing through the day.
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 5.5 vs Claude Fable 5.1: quick answers
Which is better, Claude Opus 5.5 or Claude Fable 5.1?
It depends on what you measure. Of the 6 public leaderboards that rate both, Claude Opus 5.5 scores higher on 5 and Claude Fable 5.1 on 1. Claude Opus 5.5's widest lead is on LLM Stats; 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 Opus 5.5 is at 100 and Claude Fable 5.1 at 93.4 (out of 100).
Which is newer, Claude Opus 5.5 or Claude Fable 5.1?
Claude Opus 5.5. It went live on September 22, 2026, 21 days after Claude Fable 5.1 (September 1, 2026).
Which is cheaper, Claude Opus 5.5 or Claude Fable 5.1?
Claude Opus 5.5 is cheaper on both input and output. On each vendor's own API, Claude Opus 5.5 is $4 input / $20 output per million tokens and Claude Fable 5.1 is $10 input / $50 output per million tokens. Prices as published in the models.dev catalog, as of 2026-10-08.
Which has the bigger context window, Claude Opus 5.5 or Claude Fable 5.1?
Neither. Both take 1M tokens.
How do Claude Opus 5.5 and Claude Fable 5.1 compare for coding?
On the ArtificialWatch coding index, Claude Opus 5.5 is at 96.9 (#1 of 35) and Claude Fable 5.1 at 88.2 (#3). Claude Opus 5.5 scores higher on all 3 coding boards that rate both.
Who makes Claude Opus 5.5 and Claude Fable 5.1?
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.
More comparisons
Hear the minute the next one drops. Free.
A free Chrome push the moment a new model answers on a public API, an email about 15 minutes later. Texts or a phone call on paid plans.
- Free forever
- No card
- Unsubscribe in one click
Also: the bench index · API pricing · the wire