Claude Developer Platform, on-demand conversation compaction in the Messages API repo
On September 14, 2026, the Claude Messages API added on-demand conversation compaction, in beta under the compact-2026-09-04 header. Sending a top-level compaction parameter returns a signed summary block covering the messages sent so far, kept recent turns stay word for word, and the compaction can run in the background. On models with preserved thinking, the thinking in kept turns can stay valid.
What it does for you: This is a native, Anthropic-signed alternative to what Axion's context-mode plugin does by hand today: shrinking a long agent session before it runs out of context. Because compaction runs on demand and in the background, a long Hermes or Axion run could compact mid-task instead of hitting a hard context wall, which is exactly the failure mode that broke the scout newsletter itself in August 2026.
In practice: A first-party fix for a problem YY has already paid for in dead runs, worth a real trial rather than a shelf item.
For: Both runtimes. It is a plain Claude API parameter, callable from Claude Code, from a raw SDK script, or from Hermes wherever it calls the Messages API directly.
Verdict: build now. Low integration cost, official and signed, and it targets the same context exhaustion failure this very skill was rebuilt to avoid.
Build #1 Claude Developer Platform, on-demand conversation compaction in the Messages API: use the ai-implementation-build-intake skill to build this safely. Source: https://docs.claude.com/en/release-notes/overview.md. Save canonical skill/agent under AXION\Skills and AXION\Agents.
Source · Shipped September 14, 2026, beta header compact-2026-09-04, one top-level compaction parameter on the Messages API.