CC 2.1.128 Release: New Built-in Background Agent, C# Beta Support, and Model Deprecations
Claude Code (CC) 2.1.128 ships with +1406 tokens, focusing on agent prompt restructures, API reference updates, and model deprecations.
New Agent Instructions: Background Jobs & Onboarding
The old background-job behavior system prompt is replaced with built-in background-agent instructions. Key behaviors:
- Progress narration during background execution
- Tool-result restatement after each step
- Delegation of noisy investigation subtasks
- Explicit status signals:
result:,needs input:, orfailed:
New onboarding-guide closing instructions upload the finalized ONBOARDING.md via ShareOnboardingGuide, handle existing-guide and unavailable-tool cases, and return the team share link.
New Tool Description: RemoteTrigger
The RemoteTrigger tool provides a claude.ai remote-trigger API for listing, reading, creating, updating, and running scheduled remote agent routines — without exposing OAuth tokens.
C# Beta Support
The Claude API reference now documents beta C# tool-runner and Managed Agents support via BetaToolRunner and client.Beta.Agents/Sessions/Environments.
Go & Java SDK Updates
- Go: Adds typed model constants, updates adaptive thinking syntax, and documents the beta advisor tool parameter.
- Java: SDK version updated from 2.17.0 to 2.27.0; added beta advisor tool guidance.
Model Catalog Changes
Claude Sonnet 4 and Claude Opus 4 are deprecated. Recommended replacements:
- Opus 4 → Opus 4.7 or Sonnet 4.6
- Older Sonnet models → Sonnet 4.6
The skill guide Building LLM-powered applications with Claude refreshes the current-model table to Opus 4.7, Opus 4.6, Sonnet 4.6, and Haiku 4.5.
Other Notable Changes
- Removed: Session memory update instructions and the structured
summary.mdsession memory template. - Agent thread notes: Instructs agent threads to return reports/summaries/findings directly in the final message instead of writing
.mdfiles. - Edit tool: Hardcodes the Read-output line-number prefix format as "line number + tab" in indentation-preservation guidance.
- ReadFile tool: Always appends the additional read note placeholder at the end of empty-file warnings.
- Claude API SDK references: Added structured refusal stop-details guidance across Python, TypeScript, C#, Go, Java, PHP, Ruby; added programmatic API error type guidance for Java, PHP, Ruby.
- Model migration guide: Adds Opus 4.7 as the recommended target and adds a tuning check to parse tool inputs as JSON instead of matching serialized raw strings.
📖 Read the full source: r/ClaudeAI
👀 See Also
Claude Pro User Reports 5-Hour Usage Window Burned on Single Prompt with No Output
A Claude Pro user reports that a single prompt consumed their entire 5-hour usage window, returning only planning text and no deliverable. The incident highlights issues with token consumption during internal reasoning and lack of safeguards.
Anthropic Pauses Claude Agent SDK Credit Change After User Feedback
Anthropic emailed users today to say they are pausing the planned change that would move Agent SDK, claude-p, and third-party apps to a dedicated monthly credit instead of drawing from subscription rate limits.
Bloomberg Reports on AI Coding Agents and Productivity Concerns in 2026
A Bloomberg article from February 2026 discusses AI coding agents like Claude Code and reports on a 'productivity panic' in the tech industry. The article received 44 points and 14 comments on Hacker News.
Claude Set a Real Alarm on Android via Intent System — No Hacking, But Transparency Issues Remain
Claude AI used Android's normal intent system to create a native alarm in the Samsung Clock app. The user initially feared a breach, but it's standard app-to-app communication. The lack of upfront disclosure about device-level actions raises transparency concerns.