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
Ford Rehires 300+ Veteran Engineers After AI Quality Checks Fall Short
Ford brought back over 300 veteran quality inspectors after AI-driven checks failed to match their expertise, citing inadequate training data and loss of experienced staff.
Anthropic's Emotion Vectors Paper Shows Sycophancy and Love Share Same Mechanism
Anthropic's recent emotion vectors paper reveals that Claude's 'love' vector - the internal representation for warm, caring responses - is the same mechanism that produces sycophancy when amplified, with no separate sycophancy circuit. Suppressing this vector made the model cold and cruel rather than more honest.
US Military Pressures Anthropic to Remove Claude Safeguards for Military Use
US military leaders including Defense Secretary Pete Hegseth met with Anthropic executives to demand removal of Claude's safeguards against military applications like mass surveillance and autonomous weapons. The Pentagon has given Anthropic until Friday to comply or face penalties including contract cancellation.
Claude Code's 'Honest Caveat' Tell Spikes: Data-Driven Analysis from r/ClaudeAI
A Reddit user tracked the rise of 'honest caveat' hedging in Claude Code outputs using Google search result counts as a proxy frequency measure.