Claude Code v2.1.261 repo
Anthropic's September 2026 Claude Code release train. v2.1.257 (September 1) set Claude Fable 5.1 as the default model with expanded context. v2.1.260 (September 3) added a side by side diff panel for uncommitted changes. v2.1.261 (September 4) set Opus 5 as the default for seat based Enterprise subscriptions and shipped new policy and skill diagnostics. The same window also carries four subagent reliability fixes: a SendMessage wake routing bug where the resume notification went to the main conversation instead of the resumed subagent, transcript loss on an in process teammate during long API retries, subagents failing to auto continue after a mid stream cut from sleep or a dropped connection, and nested background subagent results not persisting into the parent transcript.
What it does for you: Axion runs entirely on Claude Code, so this is a zero engineering upgrade: pull the update and the diff panel, skill diagnostics, and the subagent fixes apply immediately. The SendMessage wake fix in particular touches the exact resume pattern this session already depends on for handing work back to a subagent, so it directly reduces a class of bug YY has likely hit without a clear cause.
In practice: A workmanlike patch train rather than a headline release, the kind of update that is easy to skim past in a changelog but that quietly fixes the plumbing under long running agent sessions.
For: Claude (Axion). This is the Claude Code binary itself, the harness Axion runs on today. Hermes could pick up the same harness later, so it counts as both stack's likely daily driver rather than a one off tool.
Verdict: build now. No new code or setup, just taking the update, and the subagent fixes address failure modes that map directly onto how this workspace already uses SendMessage and background agents.
Build #1 Claude Code v2.1.261: use the ai-implementation-build-intake skill to build this safely. Source: https://www.havoptic.com/tools/claude-code. Save canonical skill/agent under AXION\Skills and AXION\Agents.
Source · v2.1.257 shipped September 1, 2026, v2.1.260 on September 3, v2.1.261 on September 4, per aggregated changelog trackers citing the official release notes.