First-rate technical account by **Jarred Sumner**, creator of **Bun** (JS/TS runtime, >22M downloads/month), on the **complete rewrite of Bun from Zig to Rust in 11 days** (May 3→14, 2026) driven by **Claude** — an exceptional case study in AI-assisted software engineering **at industrial scale**. Motivation: a recurring class of bugs (use-after-free, double-free, leaks) arising from the mix of GC-managed memory (JavaScriptCore) and manual memory (Zig); in **safe Rust**, these bugs become **compile errors** with automatic cleanup (`Drop`/RAII) — "a better feedback loop than a style guide." Rejecting the dogma that "a rewrite is always a bad idea" (a year of bugfix freeze for 3 engineers), Sumner chooses a **mechanical port** (preserve the architecture, minimal behavior change) validated by the **existing test suite, written in TypeScript and therefore language-independent** (60,624 tests, 1.39M `expect()` assertions, 0 tests removed, 6 platforms). The harness: **~50 dynamic workflows** in **Claude Code**, *write → 2+ adversarial reviewers → apply* loops, up to **64 Claude instances in parallel** (4 worktrees × 16), with **PORTING.md** + **LIFETIMES.tsv** generated in preparation. Numbers: **6,502 commits** (peak 695/h, 58/min, ~1,300 lines/min), final diff **+1,009,272 lines**, ~16,000 compile errors treated as a queue, **5.9B uncached input tokens + 690M output ≈ $165,000**. Key methodological levers: **adversarial review** (a second Claude, separate context, sees only the diff, tasked with finding why it's wrong — catches subtle bugs that are *semantically* different but *syntactically* identical) and the principle **"fix the process that generates the code, not the code by hand."** Model used: a pre-release of **Claude Fable 5** (Mythos class). Since the merge: **11 rounds of Claude Code security review**, 24/7 coverage-guided fuzzing (100B executions → ~15 PRs), **4% `unsafe` code** (78% on a single line), **19** known regressions fixed. In production: Claude Code v2.1.181, the first release on Bun-in-Rust, **+10% faster startup on Linux**. Disclosed upfront: **Bun was acquired by Anthropic in December 2025**.
#Bun#Jarred Sumner#Zig-to-Rust rewrite
Jarred Sumner (créateur de Bun ; travaille chez Anthropic depuis le rachat de Bun en décembre 2025)
Fourth installment in the ADLC series: Williams reframes code review as adversarial "prosecution" rather than collaborative evaluation. Charter agents to refute ("find what's wrong"), deploy single-lens reviewers with fresh contexts (correctness, security, contract compliance, spec alignment, test quality), act only on verified findings (reproduced by a failing test), and loop until two consecutive passes yield zero findings. Measure calibration by planting known bugs, mutation-testing style. Exit gate: zero open findings, two dry passes, green tests, empty test diff.
Engineering write-up from Anthropic's **Data Science & Data Engineering** team (Chen Chang, Clement Peng, Justin Leder, Johanne Jiao, Josh Cherry) published on **June 3, 2026** on the Anthropic blog (*Enterprise AI* category, focus on **Claude Code**). **Headline result**: ***"95% of business analytics queries are automated by Claude, with ~95% accuracy in aggregate"*** (up to **~99%** in certain domains). **Core problem**: analytics is **not** code — *"there's often only a single correct answer using a single correct source"* — it requires **mapping a user question to precise, up-to-date entities** in the data model. Three **failure modes**: (1) **concept↔entity ambiguity** (e.g. *"active users"*: which actions? exclude fraudsters? which window?); (2) **staleness** (assets and the agent's knowledge become *"subtly wrong"*); (3) **retrieval failure** (*"80% of failed queries had the information present in the corpus"* but unfindable). **Solution = a 4-layer "agentic analytics stack"**: (L1) **Data foundations** — dimensional modeling, **canonical datasets** *"single source-of-truth"*, metadata *"as a first-class product"*, integrity via CI/CD; (L2) **Sources of truth** in decreasing order of trust — **semantic layer** (the agent is *"structurally required (by skill instruction) to leverage the semantic layer first"*), lineage graph, **query corpus** (distilled into structured docs, **not** raw retrieval), business context (knowledge graph: roadmaps, decision logs, org); (L3) **Skills** — the decisive lever: ***"without skills … didn't exceed 21% … Adding skills gets these numbers consistently above 95%"***; structured **in pairs** (*Knowledge skill* = router to ~30 reference files; *Unbook skill* = senior analyst workflow: clarify → find sources → execute → **adversarial review**); **colocated** maintenance (*"a code-review hook flags any reporting-model change that doesn't touch a skill file"* → **~90% of data PRs include a skill change**); (L4) **Validation** — offline evals (threshold ~90% to launch an agent, target ~100%), **ablation testing** (notable negative result: raw grep across thousands of SQL files → accuracy moves *"less than a point"*), online (adversarial review: **+6% accuracy, +32% tokens, +72% latency**), **provenance footers** (source tier + freshness + ownership), **active correction harvesting** (scheduled agents scanning channels to draft markdown fixes). **Strategic insight**: *"documentation generated, definitions owned by humans"* — letting the LLM **define** metrics was *"net-negative"*. **Minimal starting point**: a handful of canonical datasets + a few dozen evals + a *thin knowledge skill* capture *"most of the upside"*. Strongly converges with [[shihipar-claude-code-lessons-building-skills-2026-06-03]] (skills = folders, Gotchas, hooks), the *systems around the model* doctrine of [[dropbox-okumura-beyond-code-generation-engineering-productivity-ai-agents-2026-05-28]], the **semantic layer / ontology** of talisman-modern-data-101-ontology-pipeline-refresh-2026-05-04 and seale-semantic-agent-model-harness-ontology-data-2026-04-17, the *context development lifecycle* of debois-tessl-context-development-lifecycle-ai-coding-agents-2026-02-19, and the UDA/knowledge graph of netflix-uda-unified-data-architecture-knowledge-graph-2025-06-12.
#self-service analytics#agentic data analytics#Claude Code
**Chen Chang · Clement Peng · Justin Leder · Johanne Jiao · Josh Cherry** — équipe **Data Science & Data Engineering d'Anthropic**. Article publié le **3 juin 2026** sur le blog Anthropic (claude.com/blog) · catégorie *Enterprise AI* · ~5 min de lecture.