Engineering guides and deep dives on Claude - short how-tos and long-form breakdowns.
"Compacted while idle, before the prompt cache expired" means Claude Code summarized a 200k+ session you walked away from. Set "idleCompaction": false (v2.1.290+) or take control with the API's compaction parameter.
Opus 5.5 and Sonnet 5.5 break old request code: disabled thinking, forced tool_choice and the old computer-use tool now return a 400. Per-model checklist.
Anthropic's 5.5 guides name four prompt habits that now backfire. /doctor prompt-audit found none in my repo - it found subagents for another workspace.
A rule in Claude Code's auto memory held 3/3 runs until the user contradicted it, then failed 0/3 - the same score the identical rule got in CLAUDE.md.
Opus 5 keeps the $5/$25 price of Opus 4.8 with near-Fable agentic quality - within 0.5% of Fable on CursorBench at half the cost per task.
OS-level Bash sandboxing cut Anthropic's permission prompts ~84%, but /sandbox only wraps Bash. Pick the right isolation tier and deny credential reads.
Channels are MCP servers that push Telegram, Discord, iMessage, or webhook events into your open Claude Code session. Needs v2.1.80+ and an allowlist.
A practical map of Claude Code’s shortcuts, prefixes, session commands, and CLI flags - ordered like a real terminal cheatsheet.
Claude Code ships 46 built-in tools and only 14 ask for permission: the read/mutate split, daily gotchas, and ToolName(specifier) rules to restrict them.
Fable 5 is GA at $10/$50 per million tokens with a 1M context - and refusals arrive as HTTP 200, so integrations need refusal handling and a fallback.
/goal sets a completion condition; Claude keeps going until a separate fast model (Haiku by default) confirms it from the transcript. Needs v2.1.139+.
Plan mode makes Claude Code read and plan without editing until you approve (Shift+Tab). It blocks the edit tools - but shell commands can still write.
Claude Code runs a gather→act→verify loop that fills context before you type. Compaction, /clear, and subagents are the official levers for what sticks.
Fable 5.1 for the hardest reasoning, Opus 5.5 to orchestrate at $4/$20, Sonnet 5.5 as the default worker, Haiku 4.5 for parallel grunt work. Pick by job.
Sonnet 5 is the default on Free and Pro at $2/$10 per million tokens - close to Opus 4.8 on Anthropic's launch benchmarks at 40% of the Opus input price.
Claude Code runs up to a 1M-token window, but a bigger window doesn't fix a cluttered one - every turn replays history and quality drops before the cap.
A bloated CLAUDE.md gets filtered out as noise. Keep it to universal instructions and move everything else behind progressive disclosure.