Anthropic ·
Messages API adds on-demand conversation compaction
Published by Nova3 AI Research
What shipped
On 2026-09-14, Anthropic introduced on-demand conversation compaction in the Messages API on the Claude API in beta with the compact-2026-09-04 header, using a top-level compaction parameter to return a signed compaction block for placement first in later requests in place of the summarized messages.
Anthropic release notesWhat this means for your business
Test compaction against long conversations with known requirements before replacing message history in production. Check whether summaries retain the details needed for subsequent work, and preserve recent turns verbatim where necessary.
Still open
Beta status is explicit, but the excerpt does not establish pricing, regional availability, a complete supported-model list, or measured cost savings.