Claude Code Best Practices (Boris Cherny)

Verification: The Quality Multiplier

"Give Claude a way to verify its work. If Claude has that feedback loop, it will 2-3x the quality of the final result." -- Boris Cherny

Always give Claude a way to validate its work:

Complexity	Method	Example
Simple	Bash command	npm run lint, npm run typecheck
Moderate	Test suite	npm test, pytest, go test
Complex	Browser/Simulator	Playwright, Chrome DevTools, mobile emulator

Integration: PostToolUse hooks (auto-format, type-check, lint), PreToolUse on commit (mandatory tests), QA agents (/qa:qa-audit).

Recommended Model

"I use Opus with adaptive thinking for everything." -- Boris Cherny

(Fable 5 sits one tier above Opus 4.8 for the hardest long-horizon work — see the table below.)

Context	Model	Rationale
Most demanding / long-horizon autonomous work	Fable 5 (claude-fable-5)	Anthropic's most capable model — deepest reasoning, long-horizon agentic runs. Reach for it deliberately: ~$10/$50 per MTok (2× Opus 4.8)
Complex tasks (default)	Opus 4.8	Most advanced reasoning, adaptive thinking, 1M context, xhigh effort
Audits, analyses, high-volume agentic work	Sonnet (Sonnet 5)	Near-Opus 4.8 quality at a fraction of the cost — 1M context, $2/$10 per MTok intro through 2026-08-31 (then $3/$15) vs Opus $5/$25. Claude Code's default model since 2026-06-30
Simple tasks	Haiku	Fast for trivial operations

Fable 5 vs Opus 4.8: Opus 4.8 stays the default for complex work. Fable 5 (1M context by default, 128K output, same tokenizer as Opus 4.8) is a costlier escalation — 2× Opus per token — for the hardest long-horizon tasks, not a drop-in replacement.

Sonnet 5 (since 2026-06-30): Claude Code's own default is now Sonnet 5 — the most agentic Sonnet yet, ~Opus 4.8-level on many tasks at roughly a third of the cost, with a native 1M context. The sonnet alias absorbs it automatically (no agent-frontmatter change). This foundation still recommends escalating to Opus 4.8 for complex/critical work (TDD, Audit, architecture) where the quality delta pays off, and reserving Sonnet 5 for audits, analyses, and high-volume agentic passes where its price/perf shines.

✅ Availability (July 2026): Fable 5 is generally available again. It was briefly export-control-suspended on 2026-06-12 (no access for foreign nationals); the directive was lifted on 2026-06-30 and Fable 5 returned to global availability on 2026-07-01 across Claude Platform, Claude.ai, Claude Code and Claude Cowork. (Mythos 5 remains restricted to a subset of US organizations.) Opus 4.8 stays the default not for availability reasons but because Fable 5 is a costlier, deliberate escalation (2× Opus). (Anthropic statement)

Proactively flag the escalation. When a session turns into a long-horizon chantier — a multi-PR migration, a deep audit, or a large refactor that visibly exceeds Opus 4.8's comfort zone — say so and suggest escalating the model to Fable 5 (/model, or relaunch with --model claude-fable-5). It is a deliberate, costlier choice (2× Opus) and there is no fable tier alias, so Claude cannot switch itself mid-session — surface the recommendation and let the user decide. Don't suggest it for routine work where Opus 4.8 is the right default.

Advanced Prompting

Avoid	Prefer
"Fix this bug"	"Fix the null pointer in getUserById when user doesn't exist"
"Make it better"	"Reduce the time complexity from O(n^2) to O(n log n)"
"Add error handling"	"Add try/catch for network errors with retry logic (3 attempts, exponential backoff)"

Techniques: "Grill me on these changes", "Prove to me this works", "Knowing everything you know now, implement the elegant solution".

See docs/guides/PROMPTING-GUIDE.md for the complete guide.

Effort Levels

Match the level of reasoning to the task.

Task	Effort	Why
Exploring code, reading files	low	No need for deep reasoning
Implementing a standard feature	medium	Speed/quality balance
Designing an architecture, audit, complex debug	high	Deep reasoning required
Critical system architecture, advanced security audit	xhigh	Maximum reasoning (Opus 4.8 required)

Command: /effort low, /effort medium, /effort high, /effort xhigh (interactive slider).

Effort tunes reasoning depth on the current model; it is not a model upgrade. For the hardest long-horizon work, escalating the model to Fable 5 (claude-fable-5, ~2× Opus 4.8) is the distinct, costlier lever — see "Recommended Model" above.

Automatic Memory (CLI 2.1.76+)

Claude Code automatically remembers preferences, decisions, and project context in ~/.claude/memory/.

Memorize (auto)	CLAUDE.md (git)	Rules (auto-activated)
Personal preferences	Project conventions	Per-language rules
Architecture decisions	Mandatory workflow	Code patterns
Team context	Documentation references	Verification checklist

Do not duplicate: if it is in CLAUDE.md, no need to memorize it. Use "remember that..." to force an explicit memorization.

Note (since Code with Claude 2026, May 6): Anthropic also ships Auto Dream / Dreaming, a managed memory feature where a background subagent reviews recent transcripts and consolidates the memory directory between sessions. It is complementary to the file-based system above: Auto Memory captures notes during work, Auto Dream cleans them between sessions. See the Claude managed agents blog post and the Dreams API doc.

Parallel Sessions

"The single biggest productivity unlock." -- Boris Cherny

Use git worktrees for 5+ Claude Code sessions in parallel. See the git-worktrees skill for details.

Context Management

Situation	Action	When
Long session, intact context	/compact	Between phases (Explore → Plan → TDD)
Total topic change	/clear	New unrelated task
Normal session	Let it be	Auto-compaction if needed

Quick Recovery

If a refactoring breaks everything: /rewind (or /undo, equivalent alias) returns to the last stable state. Faster than git stash or git checkout. Checkpoints saved automatically before each modification.

Since CLI 2.1.141, the Rewind menu also exposes a "Summarize up to here" entry that compresses earlier turns while keeping the recent ones intact — useful when the issue is context bloat rather than a broken change.

Session Resume

/recap generates a summary of the current session — decisions made, files modified, work state. Useful to resume a session after a break or a /compact.

Situation	Action
Return after a break	/recap to recover the context
After /compact	/recap to verify what was kept
Onboarding on an existing session	claude --resume <id> then /recap

Configurable via /config (enable/disable automatic recap on resume).

Token Optimization

Prompt Caching 1h (CLI 2.1.108+)

The ENABLE_PROMPT_CACHING_1H variable enables a 1-hour prompt cache instead of 5 minutes. Significantly reduces costs for long sessions.

Enable in .claude/settings.local.json:

{
  "env": {
    "ENABLE_PROMPT_CACHING_1H": "1"
  }
}

Compatible with API key, Bedrock, Vertex, and Foundry. Alternative: FORCE_PROMPT_CACHING_5M to force the 5-minute TTL (useful if telemetry is disabled).

Quick Command

/work:work-commit-push-pr "description" -- commit + push + PR in a single command.