Two unannounced Claude models just surfaced in Anthropic's API — and one may already beat Opus 5

Anthropic's next lineup has leaked the old-fashioned way: developers spotted two never-announced models, claude-marshmallow-eap and claude-melon-eap, sitting in the company's API. Multiple developers confirmed both codenames through API access and Discord, and early testers report that Marshmallow's conversational performance already edges out Opus 5 — Anthropic's current flagship, released barely a month ago. Neither model carries a Fable-class designation, so community consensus points to them as the next rungs on the Opus and Sonnet ladders — with TheWinCentral speculating "Marshmallow" is an early Claude Opus 5.1 and "Melon" a Claude Sonnet 5.1.

The "-eap" suffix marks both as Early Access Program builds: internal test stages opened to only a small circle of developers. That framing matters, because codenames that appear in a public API are neither final nor committed — they can be renamed, merged, or cancelled entirely. But the circumstantial evidence for an imminent refresh is strong. Opus 5 shipped July 24 and Sonnet 5 on June 30; a new pair entering EAP barely a month later would push Anthropic's iteration cadence to roughly a major update every two weeks this year. Even the internal naming scheme has shifted — previous leaks used animal codenames like "Fennec" for Sonnet 5.5, while this pair switches to foods, which some read as a sign the models belong to a fresh development branch.

The timing lands at a delicate moment. Rivals are cutting prices to court cost-sensitive enterprise buyers, Anthropic's IPO paperwork is reportedly weeks away, and its own users have been grumbling about silent quality changes — a controversy over Claude Code quietly remapping "high" reasoning effort blew up just yesterday. Leaking your next-generation models into the wild is usually an accident; leaking them this loudly, right before a public listing, looks almost like a rehearsal.

What would it take for you to switch from your current Claude tier — a smarter Marshmallow, or a cheaper Melon? Tell us in the comments.

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Akhetonics says its all-optical CPU reaches a customer in 2026

The Week in AI — October 5–11, 2026

Drone strike shuts a third Yandex data center, taking YandexGPT offline

Agent teams cost up to 5x more, barely score higher