●TOOLSWAP — Mid-conversation tool changes are in beta: add or remove tools between turns while keeping the prompt cache intact, on Fable 5, Mythos 5, Opus 4.8, and Opus 5●FALLBACK — The fallbacks parameter gained a default mode that applies Anthropic's recommended fallback models per refusal category, with server-side fallback also in beta●ADDDIR — A new DirectoryAdded hook fires right after /add-dir or the SDK register_repo_root request registers a working directory mid-session●MCPERR — Entries skipped by --mcp-config validation now surface as mcp_server_errors in the headless stream-json init event, and terminal runs print a startup warning●FANOUT — Concurrently running subagents are now capped at 20 by default, and hitting --max-budget-usd denies new spawns while halting the background agents already running●OPUS5 — Claude Opus 5 ships with a 1M-token context window, 128K max output, thinking on by default, and the same pricing as Opus 4.8●TOOLSWAP — Mid-conversation tool changes are in beta: add or remove tools between turns while keeping the prompt cache intact, on Fable 5, Mythos 5, Opus 4.8, and Opus 5●FALLBACK — The fallbacks parameter gained a default mode that applies Anthropic's recommended fallback models per refusal category, with server-side fallback also in beta●ADDDIR — A new DirectoryAdded hook fires right after /add-dir or the SDK register_repo_root request registers a working directory mid-session●MCPERR — Entries skipped by --mcp-config validation now surface as mcp_server_errors in the headless stream-json init event, and terminal runs print a startup warning●FANOUT — Concurrently running subagents are now capped at 20 by default, and hitting --max-budget-usd denies new spawns while halting the background agents already running●OPUS5 — Claude Opus 5 ships with a 1M-token context window, 128K max output, thinking on by default, and the same pricing as Opus 4.8