The gateway fix is the headline: some proxies and Anthropic-compatible servers refused requests that carried the effort-2025-11-24 beta value or system messages mid-conversation, and Claude Code now retries without them.
The cleanupPeriodDays bug is the one to know about if you keep sessions forever. With a very large value, background cleanup could delete recent files, such as pasted images.
Other changes: the Monitor tool and plugin monitors now work on Bedrock, Vertex and Foundry, and with telemetry turned off. Compaction after a "Prompt is too long" error no longer keeps big blocks of base64 or SVG that made the next request fail too. File read permission prompts now show where a symlink points. On Windows, a PreToolUse or PermissionRequest hook could let a tool call through when Git Bash was missing and the hook command was only quoted strings; that's fixed.
One independent check (AI Dev Pulse, Saturday morning) found 2.1.310 on npm's latest and next tags while stable was still on 2.1.308.