Fable 5 costs 10 dollars per million input tokens against 5 for Opus 4.8, output is 50 vs 25
SWE-Bench Pro gap is 11.1 points, and FrontierCode more than doubles at 29.3 vs 13.4
Same API surface with one new 400: explicit thinking disabled rejects on Fable 5, omit the field
Cache minimum drops to 2048 tokens on Fable 5 while Opus 4.8 needs 4096 to cache at all
My routing: Fable 5 for long autonomous runs and research, Opus 4.8 stays the daily default
Twice the price for the same request shape. That is the Claude Fable 5 deal on paper, and it makes the model easy to dismiss as an expensive trophy. I have been running Fable 5 and Opus 4.8 side by side since the June 9 launch, and the split is cleaner than I expected. This is the comparison I wanted on day one: numbers, code differences, and the routing rules I actually adopted.
The Score: Benchmarks Side by Side
Start with what doubled and what did not.
Benchmark
Fable 5
Opus 4.8
SWE-Bench Pro (real GitHub tasks)
80.3%
69.2%
FrontierCode (production-standard)
29.3%
13.4%
Core Analytics
first past 90%
10 points lower
Everyday spreadsheet suite
wins at every effort level
25-30% slower
The pattern matters more than any single row. On saturated work, the gap is small: Anthropic's own ViBench numbers show standard vibe-coding requests nearly maxed out, and Opus 4.8 already one-shots those. On hard work, the gap explodes. FrontierCode is the telling row, because 13.4 to 29.3 is not an increment, it is a different tier of task becoming solvable.
Two non-coding results moved me. On long Slay the Spire runs, persistent memory helped Fable 5 three times more than it helped Opus 4.8, and it reached the final act three times more often. That is the long-horizon coherence story in miniature: the model gets more out of its own notes. And on the Hebbia finance benchmark plus document reasoning, Fable 5 posted the highest scores measured, which matches what I see on dense PDF extraction. FrontierBench, built specifically for long-horizon reasoning, completes the sweep with Fable 5 on top.
For the baseline this is being measured against, I broke down the Opus 4.8 release in , Fable 5 just added a tier above it.
Security-adjacent work is the funny one. Fable 5 routes cybersecurity requests (vulnerability discovery, exploit analysis, attack planning) to Opus 4.8 through its safeguard classifiers anyway. The classifiers trigger in under 5 percent of sessions overall, but security work lives inside that 5 percent by definition. If your workload is security review, you would pay Fable prices for Opus answers. Skip the middleman and run Opus 4.8 directly there. And if you are unsure whether your traffic trips the handoff, check the model field on the responses you get back, because the swap is otherwise silent.
Latency-sensitive iteration also stays put, because fast mode only exists on Opus. For tight edit-test loops in Claude Code, Opus 4.8 with fast mode still feels better than Fable 5 at standard speed, and for what day-to-day Opus work looks like, .
My whole dual-model setup, routing hooks included, ships as .
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