{"version":"2.1.219","anchor":"new-migrating-to-opus-name-migration-guide-with-two-breaking","canonical_anchor":"new-migrating-to-opus-name-migration-guide-with-two-breaking","heading":"New \"Migrating to {{OPUS_NAME}}\" migration guide with two breaking changes","tier":"notice","area":"Skills","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.219\/e\/new-migrating-to-opus-name-migration-guide-with-two-breaking","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.219","markdown":"### New \"Migrating to {{OPUS_NAME}}\" migration guide with two breaking changes\n\nA migration guide now spells out the two thinking-related changes that break existing API request code.\n\n**What**\n\nshared\/model-migration.md gains a section for the new Opus covering the two behaviours that break existing request code.\n\n**Details**\n\n- Breaking change 1: thinking is on by default when `thinking` is omitted, a silent cost and truncation change measured against `max_tokens`.\n- Breaking change 2: `thinking: {type: \"disabled\"}` is accepted only at effort `high` or lower; pairing it with `xhigh` or `max` returns 400, validated per request.\n- Documents disabled-thinking failure modes: tool calls emitted as plain text, and `<thinking>` tag leakage.\n- Also notes a 512-token cache minimum, a separate rate-limit bucket, and adds a [BLOCKS]\/[TUNE] checklist.\n- Older Opus rows in the migration table now all target the new ID.\n\n**Evidence**\n\n`### Breaking change 2: disabling thinking is capped at`\n\n- Area: Skills\n- Tier: You'll notice\n- Useful: 3\/5\n- Signal: 0\/5"}