Claude Code August 2026: Sonnet 5 Default, Fork Subagents, Dataviz Skill, Auto Draft PRs
Sonnet 5 is now the default Claude Code model with native 1M-token context. Fork-mode subagents are on by default in interactive sessions — a fork subagent inherits the full conversation and prompt cache with no setup required, toggle off with CLAUDE_CODE_FORK_SUBAGENT=0. v2.1.198 shipped two skill-related changes: the /dataviz skill for chart and dashboard design (includes a runnable color-palette validator), and background agents in worktrees now automatically commit, push the branch, and open a draft PR when they finish — no prompt, no pause. Cross-session @ mentions let you ping another Claude session by name mid-conversation.
Sonnet 5 at 1M-token context changes the unit economics of large-codebase work — a full monorepo fits in context without chunking. Fork subagents on by default means parallel agent work stops requiring explicit configuration for the common case. The worktree auto-PR behavior is the most impactful workflow change for teams: background agents now hand off finished work to human review in GitHub without a second command. The /dataviz skill plugs a real gap — chart design has been a persistent weak point for coding agents, and the color-palette validator makes design iteration testable rather than purely visual.
To use fork subagents: nothing to configure — they're on by default. To disable: set CLAUDE_CODE_FORK_SUBAGENT=0. For the /dataviz skill: type /dataviz in any session to activate; it guides chart type selection, color palette, and accessibility. For worktree auto-PR: run `claude agents` in a worktree-based project; the background agent commits and pushes when done and opens a draft PR — check your GitHub notifications. For cross-session mentions: type @ and a session name in your prompt; Claude routes the message via SendMessage.