New model IDs 'claude-fable-5-1' and 'claude-mythos-5-1' detected in Anthropic's Claude Co

EXHIBIT 1101 · FLASH

Sep 1, 2026 18:38 UTC binary @anthropic-ai/claude-code-darwin-arm64

New model IDs 'claude-fable-5-1' and 'claude-mythos-5-1' detected in Anthropic's Claude Code binary, alongside numerous internal and experimental feature flags.

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anthropic's claude-code binary got an update, and it looks like there are mentions of new models: 'claude-fable-5-1' and 'claude-mythos-5-1'. could be internal tests, but interesting to see!

deep dive into the latest claude-code binary update reveals several 'internal' and 'experimental' flags, plus new model ids like 'claude-fable-5-1'. curious what they're brewing internally at anthropic.

⚠️ FROM COMPILED BINARY — lower confidence, verify before posting. (May include bundled-dependency strings, not just first-party changes.) @anthropic-ai/claude-code-darwin-arm64 2.1.252 -> 2.1.257: +26252 strings, -17969 strings, 75 interesting [model_id] (5) + anthropic.claude-fable-5-1 + claude-fable-5-1 + claude-fable-5[1m] + claude-mythos-5-1 + us.anthropic.claude-fable-5-1 [feature_flag] (42) + ${e?Se:"Every message you send is to the user."} Worker results and system notifications are internal signals, not conversation partners \u2014 never thank or acknowledge them. Summarize new information for the user as it arrives. + --experimental-repl-await + .compute.internal + <${j0}>${r.length} background ${o} task(s) from the previous session have no completion record. ${C} They have been marked ${e}. ${I} Task ids in this notification beginning with "${Oe}" are internal scan markers, not tasks.</${j0}> + ExperimentalWarning + GIT_ASKPASSGIT_SSH_COMMANDssh -oStrictHostKeyChecking=accept-newmanifest:npm-package:internal error: entered unreachable code: PackageVersion::dep_group: unknown field@file:version + INTERNAL_IPC_PREFIX + INTERNAL_ONLY_COMMANDS + INTERNAL_PERMISSION_MODES + Internal consistency error: the ExpectCustomAsymmetricMatcher(matcherFn) was garbage collected but it should not have been!Internal consistency error: the ExpectCustomMatcher(matcherFn) is not a function! + Internal error: Unexpected stmt in for loop(()=>{throw new Error("Cannot require module "+ + InternalResolver + InternalSecureContext + Tip: The shorthand "${d.repo}" assumes github.com. `+`For an internal git host (GitHub Enterprise, GitLab Self-Managed or Dedicated, \u2026), use the full repository URL: + Worker.stmt_list set in create()internal error: entered unreachable code: generateCompileResultForCssChunk called on non-CSS chunk + [2J... casethisvoidread => jpegwebpheicaviftiffzlibboolcharflagdest-0.0-infbash ci/beta.bundiffsendpipePORT