Claude Sonnet 5.5 turns up in a third-party client's registry, and Anthropic has said nothing

Anthropic has not announced Claude Sonnet 5.5, and as of September 28 there is no pricing, model card or benchmark set for it. What exists is a string. On September 27 the leak account Lumina (@LuminaBench) posted that the API-style identifier "claude-sonnet-5-5" already sits in the model registry of Factory Droid 0.228.0, a third-party coding client, behind a feature flag, while Factory's public model list still stops at Claude Sonnet 5. The same thread says Sonnet 5.5 is in greyscale testing. That is a staging signal inside someone else's client, not a release.

What the Droid registry string actually shows

Lumina's post is precise about where the string lives and loose about what it means: the slug "is already in the latest Droid 0.228.0 model registry behind a feature flag," while Factory's public model list "still only shows Sonnet 5." A second post in the thread reads out the details packed around it, with her own warning attached: "Don't read into the credits as pricing btw."

• Context window: 872K tokens
• Maximum output: 128K tokens
• Reasoning levels: standard low -> max
• Placement: flagged in Droid 0.228.0, next to the live claude-opus-5-5 slug

Those numbers come from a registry frame inside a third-party app, not from Anthropic. Registry dumps are noisy and carry placeholders; the explainx.ai write-up published that day says plainly it did not decompile Droid 0.228.0 itself. A partner expecting an endpoint soon is not an endpoint that answers.

Greyscale, DevDay and a screenshot

The distribution half of the leak is thinner than the naming half. Lumina says Sonnet 5.5 "is in greyscale testing"; in practice that means routing a slice of traffic or allow-listing accounts, and the replies claiming some Claude Code users already reach it are the same anecdote that trails every Claude rollout. Nobody outside those buckets can check it. On r/singularity the story arrived as an image post whose title claimed a "last-minute upgrade" and a release "expected Monday" — screenshot assertions in a thread of roughly 400 upvotes and 60 comments, not reporting. The Monday-or-Tuesday timing talk tied to OpenAI DevDay is narrative with nothing behind it. What is evidenced is one string in one client build; what is claimed is routing, quality and a date.

What would settle it

Anthropic's September 22 Opus 5.5 launch said Sonnet 5.5 and Haiku 5.5 would follow "in the coming weeks," a line Reuters also reported. That is the only official timeline. Sonnet 5.5 becomes real when Anthropic publishes a model ID and pricing in its docs, a model card with benchmarks, and per-task cost tests hold up on Claude Code at a real cache-hit rate. Until then claude-sonnet-5 remains the workhorse documented since June, next to claude-opus-5-5 from this month's launch.