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Public story · 2026-07-25 · high
A separate index has Fable 5 slightly ahead, and a FrontierCode anomaly puts both scores in doubt.
Why now: The comparison surfaced in Latent Space's July 25 AINews roundup of Artificial Analysis and Epoch benchmark data.
Opus 5 opened a nearly 150 Elo lead over Fable 5 on Artificial Analysis's benchmark, per Latent Space's July 25 AINews roundup. Fable 5 edges it out on a separate index.
That Elo gap came with a 20% cut in cost per task, per Artificial Analysis. For a team picking a default coding model, that's the pitch: less spend, no capability given up. Except the benchmarks don't agree on that last part.
On the Epoch Capabilities Index, Fable 5 leads Opus 5, 161 to 159. Narrow the index to SWE-ECI, the software engineering subset, and the two tie at 161 apiece, per Latent Space's breakdown. General capability tilts to Fable 5. Coding capability is a dead heat.
Then there's the anomaly. Users benchmarking Opus 5 on FrontierCode found medium reasoning effort scoring higher than high effort. That's not supposed to happen if the benchmark tracks a real capability curve. Latent Space flags it as evaluation instability rather than a genuine result, and says it deserves more attention than it's getting.
The two scoring systems don't agree on who's ahead. Fable 5 leads by two points on ECI. They're dead even on SWE-ECI. Opus 5 is well ahead on Elo and cost. That spread is the story, not either headline number. Until someone explains the FrontierCode inversion, the SWE-ECI tie is the number worth trusting if you're picking a model to write code.
Each link below shares sources, entities, or timing with this story.
Claude Code uses Opus / Shared entities / Same source
Linked by a graph relationship (Claude Code uses Opus); both cover ECI, Epoch Capabilities Index, Fable, Opus; cite the same source (Latent Space's AINews breakdown).
Opus built by Anthropic / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover Latent Space, Opus; overlapping topics (analysi, beat, capability, opus, task).
Opus built by Anthropic / Shared entities / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Opus built by Anthropic); both cover Opus, SWE; overlapping topics (cost, opus, task).
Simon Willison uses Fable / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Simon Willison uses Fable); both cover Artificial Analysis, Fable, Opus, SWE; overlapping topics (capability, fable).
Opus built by Anthropic / Shared entities / Shared topic / Earlier coverage / Tension
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Opus; overlapping topics (against, fable).
Opus built by Anthropic / Shared entities / Shared topic / Earlier coverage
Linked by a graph relationship (Opus built by Anthropic); both cover Opus, SWE; overlapping topics (cost, engineering, opus).
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Opus; overlapping topics (beat, fable).
Linked by a graph relationship (Opus built by Anthropic); both cover Fable, Opus; overlapping topics (capability, fable).