Claude Code 2.1.220 Defaultly Switches to Opus 5, Nested Subagent Depth Expanded to 3 Layers
On July 24, 2026, Anthropic released the 2.1.220 series updates for Claude Code: version 2.1.219 switched the default model to Claude Opus 5 (1M context window), and expanded the default nested subagent depth from 1 to 3; version 2.1.218 changed `/code-review` to run as a background subagent. An early August evaluation showed that the gap between Opus 5 and GPT-5.6-Sol on Terminal-Bench 2.1 was less than 0.5 percentage points, and the competition for AI programming agents has shifted to focusing on both models and orchestration layers. This article sorts out the version changes based on the official CHANGELOG, and provides configuration instructions for subagent depth limits, concurrency upper limits and other parameters.
Read MoreModel Isn't the Decisive Factor: The Harness Battle for CLI Coding Agents in 2026
In mid-2026, the focus of the CLI coding Agent community shifted from foundation models to Harness—system prompts, retry logic, context compression, and sub-agent orchestration. On Terminal-Bench 2.1, Claude Code and Codex CLI were locked in a tight race with an accuracy rate of around 83%, and the same model could achieve scores differing by several percentage points under different Harness configurations. This paper sorts out the concept of Harness, compares four development routes including Claude Code, Codex CLI, OpenCode and Copilot CLI, and explains why context compression has become an invisible battlefield, to help developers select appropriate solutions according to their scenarios.
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