Anthropic leak: Claude Opus 5.1 / Sonnet 5.1 testers spot "Fable-class" checkpoint
Adidotdev · x · 2026-08-26
A third-party tracker reports that Anthropic's internal tester IDs "Marshmallow" and "Melon"—believed to be Claude Opus 5.1 / Sonnet 5.1—got fresh tester reads: Melon now looks like an actual Fable-class checkpoint, while Marshmallow reads as a weaker Fable or a strong Opus. Both IDs were pulled a few hours ago.
The account notes this mirrors the pre-Opus-5 pattern (fruitcake-eap and honeycomb-eap, followed by release within weeks). Opus 5 proved the playbook—matching Fable 5 on coding at less than half the cost. Two days ago these were called mid-tier; now one reads Fable-class. If Melon is the real next jump, it pressures Fable 5's pricing. Note: unverified leak.
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