Claude Code

Claude Code is Anthropic’s coding agent: a terminal-first AI tool that writes, reviews, and executes code by using tools autonomously. Created by Boris Cherny as a solo hack in 2024; released externally in February 2025; by 2026 accounts for approximately 4% of all public GitHub commits.

Origins and design philosophy

Claude Code grew out of Anthropic’s internal model development roadmap: coding → tool use → computer use. This sequence was chosen deliberately — coding is the domain where agentic capability can be studied most rigorously, and where safety can be verified most precisely.

The terminal interface was not a deliberate design choice. It was the fastest way to build alone. The team later considered other form factors but found the terminal was the only interface that could keep pace with rapid model improvement.

The first internal demo received two likes. External release in February 2025 was not immediately a hit; adoption grew slowly until the first sharp inflection with Opus 4 / Sonnet 4 in May 2025.

Core design inversion

Most LLM products treat the model as a component inside a larger system with pre-specified tool sequences. Claude Code inverted this:

“The product is the model.”

Minimal scaffolding. Minimal pre-specified tool order. The model receives tools and a goal, and decides how to use them. This is the product expression of Latent Demand form 2 (model latent demand) and Bitter Lesson — scaffolding buys at most 10–20% improvement and is typically wiped out by the next model.

Growth and impact

4% of all public GitHub commits attributed to Claude Code (Semi-Analysis, 2026) [?source]
Private repository usage estimated meaningfully higher
Daily active users have continued to accelerate (doubled in the month before the Feb 2026 interview)
At Anthropic: ~200% productivity increase (measured in PRs) despite ~4× engineering headcount growth

Features and form factors

Available across: terminal (all platforms), desktop app (code tab), iOS/Android, Slack integration, GitHub integration, IDE extensions, web.

Key features:

Plan mode — injects “please don’t write any code yet” into the prompt; model plans in dialogue before executing.
Auto-accept edits — after plan approval, the model executes without confirmation checkpoints.
Multi-Claude-ing — running multiple sessions in parallel across different tasks simultaneously.
Claude-reviewed PRs — at Anthropic, Claude reviews 100% of pull requests; human review follows.

Cowork

Claude Code’s underlying agent also powers Cowork — Anthropic’s desktop-native product for non-engineering tasks (email, project management, web forms, calendar). Cowork was built in 10 days using Claude Code itself. It ships with a sandboxed VM for safety and a Chrome integration for browser-based automation.

The same Claude Code agent runs in Cowork; the difference is packaging and the target user (non-engineers).

Safety model

Claude Code was used internally at Anthropic for 4–5 months before external release — specifically to study agentic safety in the wild, since it was the first coding agent to be broadly deployed. Anthropic open-sourced its agent sandbox (compatible with any agent) as part of a “race to the top” strategy.

The three-layer safety model Boris describes:

Alignment + Mechanistic Interpretability (training-time)
Evals (laboratory)
In-the-wild behaviour (deployment)

Practical tips (Boris Cherny’s own usage)

Use Opus 4.6 with max effort — usually not more expensive due to fewer correction loops.
Start in plan mode (~80% of tasks); auto-accept after plan is agreed.
Try all form factors; the same agent runs everywhere.
Run multiple Claudes in parallel.