{"version":"2.1.219","anchor":"two-new-api-betas-documented-scalar-fallbacks-default-and-mi","canonical_anchor":"two-new-api-betas-documented-scalar-fallbacks-default-and-mi","heading":"Two new API betas documented: scalar fallbacks: \"default\" and mid-conversation tool changes","tier":"use","area":"Skills","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.219\/e\/two-new-api-betas-documented-scalar-fallbacks-default-and-mi","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.219","markdown":"### Two new API betas documented: scalar `fallbacks: \"default\"` and mid-conversation tool changes\n\nDocs now describe two beta headers for automatic refusal fallbacks and swapping tools mid-conversation.\n\n**What**\n\nThe skill documents two beta headers that did not appear in the previous build's docs.\n\n**Details**\n\n- `fallbacks: \"default\"` sits behind `server-side-fallback-2026-07-01` and lets the server pick the fallback by refusal category; the array form stays on `server-side-fallback-2026-06-01`, and pairing either header with the other form returns 400.\n- A new tool-use-concepts section covers `mid-conversation-tool-changes-2026-07-01`: `tool_addition` and `tool_removal` blocks on a `role: \"system\"` message change the tool set between turns without invalidating the prompt cache.\n- Tools involved must be declared with `\"defer_loading\": True`.\n\n**Evidence**\n\n`mid-conversation-tool-changes-2026-07-01`\n\n- Area: Skills\n- Names: `server-side-fallback-2026-07-01`, `mid-conversation-tool-changes-2026-07-01`, `defer_loading`\n- Tier: Use it now\n- Useful: 3\/5\n- Signal: 0\/5"}