Mythos-class Claude Fable 5 arrives on GitLab Duo Agent Platform

Claude Fable 5, a Mythos-class model from Anthropic, was initially announced as available on the GitLab Duo Agent Platform, offering significant advancements over previous models, including improved first-shot correctness, long-horizon autonomy, and higher accuracy in interpreting technical content. It was designed to complete complex, multi-step tasks with fewer iterations and greater reliability, reducing the need for human oversight in AI agent workflows. Notably, Claude Fable 5 excelled in tasks such as multi-file refactors, incident investigations, and infrastructure-as-code definitions, showing enhanced bug-finding capabilities and faster incident resolution. However, as of June 12, 2026, access to Claude Fable 5 has been suspended on the platform due to a U.S. government directive, although other Claude models remain available.

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