{"version":"2.1.265","anchor":"model-1m-context-aliases-get-explicit-availability-checks","canonical_anchor":"1m-context-alias-switching-gets-structured-refusal-reasons","heading":"\/model now gives clear reasons when a 1M-context alias can't be used","tier":"use","area":"Models","scope":null,"heads_up":null,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.265\/e\/model-1m-context-aliases-get-explicit-availability-checks","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.265","markdown":"### \/model now gives clear reasons when a 1M-context alias can't be used\n\nSwitching \/model to a 1M-context alias now explains exactly why it's blocked instead of failing generically\n\n**What**\n\nWhen switching to a model alias with a 1M-token context window (a `[1m]`-suffixed alias), Claude Code now checks for three specific problems before switching, each with its own clear error message telling you what to do instead:\n\n- 1M context has been turned off via the `CLAUDE_CODE_DISABLE_1M_CONTEXT` environment variable.\n\n- The target model doesn't support a 1M-token context window.\n\n- The alias has no 1M variant for the current mode.\n\nThese checks run before the older Opus-1M-specific check that previously handled this.\n\n**Why**\n\nPreviously these failures likely surfaced as a generic error; now each case is distinguished with its own message and telemetry reason, making it clear why a 1M-context switch didn't happen and what to try instead.\n\n- Area: Models\n- Names: `\/model`\n- Tier: Use it now\n- Useful: 3\/5\n- Signal: 2\/5"}