Grok Build is xAI's Rust coding agent — 845K LOC, 8 parallel sub-agents, Arena Mode. May 2026 beta, July open-sourced (Apache 2.0) — but the direct trigger for open-sourcing was a privacy incident: it silently uploaded entire repos (including SSH keys, .env files) to Google Cloud Storage at a 27,800x traffic ratio. The exfiltration code remains in the binary, disabled only by a server-side flag.
In August 2026, it's not just five frameworks moving. Beyond OMP 2, Pi v2, Opencode 2, dsh, and Claude Code, three model makers — Google (Antigravity CLI), Meta (Muse Code), and xAI (Grok Build) — are building coding agents directly. Add Amp, Cline 2.0, and the Codex CLI Rust rewrite, and eight-plus frameworks are undergoing architecture-level changes simultaneously. Factor in 110+ total CLI tools, and H2 2026 is a divergence period for harness methodology. This article analyzes four architectural approaches, one shared direction, and one emerging trust crisis.