Updates: #API.

[NEW] Claude Fable 5 and Claude Mythos 5 · Anthropic released Claude Fable 5 and Claude Mythos 5 on June 9, 2026. Fable 5 is a Mythos-class model made safe for general use — state-of-the-art on nearly all tested benchmarks, with the `claude-fable-5` model ID. Mythos 5 is identical with cybersecurity safeguards lifted, available in limited release through Project Glasswing. Both support a 1M token context window and up to 128k output tokens by default, priced at $10/$50 per MTok. When a safety classifier declines a request, the Messages API returns stop_reason: "refusal" as an HTTP 200, and the fallbacks parameter (beta) or SDK middleware retries on another Claude model.

[NEW] What's new in Claude Managed Agents — Dreaming, Outcomes, Multiagent, Webhooks · A month after the April 8 beta launch, Managed Agents added two new features and promoted three from research preview to public beta. Dreaming (research preview) curates memory between sessions for self-improvement, and outcomes, multiagent orchestration, memory, and webhooks all ship as public beta.

[NEW] Claude Managed Agents · A new API alongside Messages that provides a pre-built agent harness and managed infrastructure — run Claude agents without building your own loop, sandbox, or tool-execution layer.