●Breaking
claude-fable-5 and claude-mythos-5 Suspended — US Export-Control Directive, Effective June 12
What changed
Three days after launching as Anthropic's most capable public models (June 9),
claude-fable-5 and claude-mythos-5 were disabled globally at Anthropic's infrastructure level. All API requests to either model ID now return HTTP 404 with the error body:{
"type": "error",
"error": {
"type": "not_found_error",
"message": "Claude Fable 5 is not available. Please use Opus 4.8. Learn more: https://www.anthropic.com/news/fable-mythos-access"
}
}
Previously, both models were fully available on the Messages API, Claude Platform on AWS, and GitHub Copilot (Fable 5 GA on Copilot since June 9). Claude Mythos 5 was available only to Project Glasswing participants. The model IDs claude-fable-5 and claude-mythos-5 are now non-functional.
TL;DR
US government export-control directive received June 12 at 5:21 PM ET requires Anthropic to block foreign national access to Fable 5 and Mythos 5; since Anthropic cannot filter by nationality in real time, it suspended both models globally — 404 returned for all callers, no timeline for restoration.
Developer signal
Two immediate actions and one longer-term decision: (1) Change your model ID today — replace
claude-fable-5 with claude-opus-4-8 and claude-mythos-5 with claude-opus-4-8. The 404 is permanent until further notice; there is no retry path. Check: environment variables (ANTHROPIC_DEFAULT_MODEL, ANTHROPIC_DEFAULT_LARGE_MODEL), hardcoded strings in config files, and any auto-mode logic in Claude Code that may have set Fable 5 as the active model. The Claude Code /model command can be used to select a different model interactively. (2) Update any fallbacks configuration — the fallbacks parameter (beta) on the Messages API was specifically documented for Fable 5 to handle stop_reason: "refusal" by re-running on a fallback model. If you configured fallbacks to route Fable 5 refusals to Opus 4.8, that fallback config is now moot but benign; update the primary model field. (3) Note the capability gap — Fable 5 was benchmarked at 95% on SWE-bench Verified vs. Opus 4.8 at 88.6%. Opus 4.8 is the recommended replacement for agentic workloads; Sonnet 4.6 works for lighter tasks with faster latency. The adaptive thinking and 1M context window are available on both. Context: On June 11 (before the suspension), Anthropic reversed a separate controversy: Fable 5 had launched with an undocumented silent fallback — when its safety classifier triggered, it was downgrading to Opus 4.8 without notifying the API caller. After user backlash, Anthropic updated the model to return stop_reason: "refusal" explicitly (matching the cyber/bio/reasoning_extraction categories already documented). This behavioral fix is now moot given the suspension, but it does mean that if and when Fable 5 returns, the explicit refusal path will be active. Important: The directive affects only Fable 5 and Mythos 5. Every other Claude model is fully operational. The June 15 Agent SDK billing split and model retirement (Sonnet 4 / Opus 4) are separate and proceed as announced.Affects you ifYou updated your application to use
model: "claude-fable-5" after its June 9 launch; you use Claude Code with Auto mode (which may have selected Fable 5 as the active model); you have environment variables or config files referencing claude-fable-5; you are a Project Glasswing participant using claude-mythos-5EffortQuick (change model ID in config/code; no other API changes required — the Opus 4.8 parameters and tools API are identical to Fable 5 with the exception of Fable 5's stop_reason: "refusal" now being irrelevant)Anthropic (official statement) | Date: June 12, 2026 (directive received 5:21 PM ET) | Link: https://www.anthropic.com/news/fable-mythos-accesshttps://www.anthropic.com/news/fable-mythos-access — confirmed by GitHub issue #68121 in anthropics/claude-code (opened June 13: "Invalid or Inaccessible Model claude-fable-5")