{"version":"2.1.287","anchor":"sdk-frames-carry-thinking-duration-ms","canonical_anchor":"sdk-frames-carry-thinking-duration-ms","heading":"SDK messages can now say how long the model spent thinking","tier":"notice","area":"SDK","url":"https:\/\/changelogs.core-directive.com\/v\/2.1.287\/e\/sdk-frames-carry-thinking-duration-ms","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.287","markdown":"### SDK messages can now say how long the model spent thinking\n\nSDK messages for a streamed thinking block can now carry a `thinking_duration_ms` field with how long it took\n\n**Unclear.** It is not confirmed that every program receiving these messages gets the field.\n\n**What**\n\nThe SDK is the toolkit programs use to run Claude Code and receive its output as a stream of messages. A message holding a single thinking block, the model's step-by-step reasoning streamed as it happens, can now carry an optional `thinking_duration_ms` field. It gives, in milliseconds, how long that block took to stream.\n\n**Why**\n\nApps built on Claude Code can show how long the model thought. The field is marked as internal, so it may not be meant for general use.\n\n- Area: SDK\n- Tier: You'll notice\n- Useful: 4\/5\n- Signal: 2\/5"}