Claude Fable 5, a new Mythos-class model from Anthropic, is now integrated into the GitLab Duo Agent Platform. This is a significant upgrade, enabling completion of complex, multi-step tasks that previous AIs struggled with, while reducing iteration cycles. Claude Fable 5 enhances features like Duo Agentic Chat and foundational agents with its improved capabilities. It is accessible across all GitLab tiers and deployment models via the AI Gateway. A key advantage is a measurable increase in first-shot accuracy for complex problems, significantly shortening development time. Claude Fable 5 also demonstrates superior interpretation of technical images and screenshots. The model offers long-horizon autonomy, sustaining productive output over extended periods and millions of tokens. This allows agent workflows to run to completion without manual intervention, as Claude Fable 5 can self-correct and manage parallel sub-agents. Engineering leaders will appreciate reduced human oversight costs and the ability to assign more challenging problems. Bug detection and incident resolution are also improved, with deeper code reasoning and more actionable review comments. Users are encouraged to leverage Claude Fable 5 on their most difficult unsolved problems. Claude Fable 5 becomes available on the GitLab Duo Agent Platform starting June 9, 2026.