What changed in Claude, Claude Code and agent tooling. Short, sourced, and read in two minutes.
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Claude Code 2.1.312 shortens the system prompt for custom model names on cloud providers and drops an OpenTelemetry event. Teams on Bedrock, Vertex or Foundry should check both.
Claude Code 2.1.311 changes where Bedrock, Vertex and Foundry model settings come from, and what ultrathink costs. Teams on cloud providers should check both.
A new API version and major SDK and CLI releases arrived on 21 October 2026. Teams that upgrade SDKs get the new version by default, plus breaking changes.
Anthropic launched user profiles on 20 October 2026. Platforms and resellers can tag each request with an end customer, so enforcement need not hit the whole organization.
The 19 October 2026 release adds guided auto mode setup, a settings comparison for Managed Agents, review levels for Code Review, and gateway tool search retry.
Fork subagents now run by default in claude -p and the Agent SDK, and prompt and agent hooks are capped at 12 at a time. Check scripted and CI use.
No access request and no beta header needed for Claude Opus 5.5 fast mode. Opus 5 and Opus 4.8 stay in preview and still need the header.
Trace Messages API requests and Managed Agents sessions in the observability tool you already use. Beta since 14 October, for any team running Claude in production.
Subagents can compact on their own schedule, workflow agents can share one model, and MCP servers get twice the room for tool descriptions.
The new small model has a 1M token context window and adaptive thinking. Several request shapes that worked on Haiku 4.5 now return a 400 error.
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