Breaking

Anthropic’s prompt-audit command targets legacy prompts for Claude Opus 5.5 migrations

September 25, 2026 at 14:16 EDT

Foundation Models
AI Agents
Software Dev & Coding

Anthropic’s Claude Code users are circulating a newly relevant one-line workflow: run /claude-api prompt-audit before carrying older prompts, skills or CLAUDE.md files into Claude Opus 5.5. The command has become a practical companion to Anthropic’s Opus 5.5 guidance because the new model is faster and cheaper than Opus 5, but can expose stale prompt patterns that once helped older models.

Sep. 22, 2026 · Anthropic

Prompt cleanup becomes part of Opus 5.5 migration

Claude Code’s /claude-api prompt-audit checks older prompts, skills and request code for patterns that can make Claude Opus 5.5 over-plan, repeat tool calls or hit changed API behavior.

40%

Lower typical Opus 5.5 running cost vs Opus 5

Additional benchmark cost cut after prompt-audit

Token context window for Claude Opus 5.5

Breaking API changes noted for Opus 5 migrations

Benchmark cost cuts stack up

18%Model switch

9%Prompt audit

In Anthropic’s customer-support benchmark, the model change cut costs first; removing legacy prompt anti-patterns added a second measured reduction.

What improves

Developers use the audit to find duplicated reasoning, stale scratchpads, over-prescriptive steps and prompt text that makes newer models repeat tool calls.

What still needs judgment

The audit proposes changes; teams still need to test removals, preserve load-bearing context and calibrate effort for their own workloads.

Migration workflow

Inventory

Prompts, skills, tools and request code

→

Audit

Find dated model patterns

→

Test

Compare behavior and usage

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