a changelog release, not a launch: it adds `CLAUDE_CODE_SUBAGENT_EFFORT` to set the effort level subagents run at instead of inheriting the session's, pooled group budgets on the Claude apps gateway (one monthly budget a group's members share, on top of each member's own limit), and `CLAUDE_CODE_DISABLE_ULTRATHINK` to turn the `ultrathink` keyword off. It also deprecates fast mode for Opus 4.8 as of October 30, 2026 — fast mode will be removed on November 30, after which fast-mode requests on Opus 4.8 return an error rather than falling back to standard Opus 4.8; the release notes direct users to Opus 5.5 to keep the speedup.