Claude Code v2.1.278: auto mode moves to a server-side classifier with no API overhead
Anthropic
Claude Code shipped v2.1.278 (Sept 19): for Claude API/Enterprise users and on Bedrock/Vertex/Foundry/gateways, auto-mode permission decisions now default to a server-side classifier with no token-bill overhead for the sandbox decision (opt out with CLAUDE_CODE_AUTO_MODE_SERVER=0). The preceding v2.1.277 added AGENTS.md support (used when a project has no CLAUDE.md) and hardened subagent output so it can no longer masquerade as session instructions. Plugins now install without running install scripts, and skills/plugins enabled on claude.ai sync into terminal sessions.
Why it matters
Permission-checking moving server-side removes the token cost of local sandbox decisions on every tool call, and AGENTS.md support ends the CLAUDE.md/AGENTS.md split for multi-tool repos.
Importance: 2/5
Notable Claude Code minor release with real behavioral changes