{"version":"2.1.293","anchor":"new-prompt-guidance-block-for-early-stopping-gated-by-tengu","canonical_anchor":"claude-haiku-5-5-model-family-recognised","heading":"Claude Haiku 5.5 added, and the haiku alias points to it on the first-party API","tier":"notice","area":"Effort","scope":"individual","heads_up":true,"url":"https:\/\/changelogs.core-directive.com\/v\/2.1.293\/e\/new-prompt-guidance-block-for-early-stopping-gated-by-tengu","release_url":"https:\/\/changelogs.core-directive.com\/v\/2.1.293","markdown":"### Claude Haiku 5.5 added, and the haiku alias points to it on the first-party API\n\nClaude Haiku 5.5 joins the model list and the haiku alias now resolves to it on Anthropic's API, while Bedrock, Vertex and other providers stay on Haiku 4.5\n\n**Unclear.** Which models receive these instructions is not shown.\n\n**What**\n\nThis build knows about a new model, Claude Haiku 5.5 (`claude-haiku-5-5`). The name appears 16 times in this build and not at all in the previous one.\n\n- The `haiku` alias, the short name that stands for the current Haiku model, now defaults to `claude-haiku-5-5` in place of `claude-haiku-4-5`. A `per_provider` map keeps `bedrock`, `vertex`, `foundry`, `mantle`, `anthropic_aws`, `anthropic_google_cloud` and `gateway` on `claude-haiku-4-5`, so only Anthropic's own API gets the new model.\n\n- The built-in model entry lists a 1M-token context window, 128000 maximum output tokens, default effort `medium`, a Bedrock id, and `claude-haiku-4-5` as the fallback on third-party providers.\n\n- A `haiku_55` pricing tier is added, listed as input 0.1 and output 0.5, with a long-prompt surcharge above 100,000 prompt tokens.\n\n- The short name `haiku-5-5` maps to the model, any id containing `claude-haiku-5-5` is recognised as it, and it gets its own family entry, `haiku55`.\n\n- A new environment variable, `VERTEX_REGION_CLAUDE_HAIKU_5_5`, sets which Google Vertex region this model uses.\n\n- A capability check that treated any model name containing \"haiku\" like `claude-opus-4-6` and `claude-sonnet-4-6` now leaves `claude-haiku-5-5` out of that group.\n\n- The model-list text in the system prompt now says \"The most recent Claude models are the Claude 5 family.\" without \"and Haiku 4.5\", and no longer maps `claude-haiku-4-5` to its dated id.\n\n- New system-prompt guidance tells the model that reasoning effort does not change how much of a request it should finish, and that it should not check in before starting a large task. It applies only to models that pass the `haiku_5_5_early_stopping_guidance` check and when the server-side flag `tengu_idempotent_wolf` is on. The flag defaults to true in the code, and nothing has been read about it.\n\n**Why**\n\nIf you use the `haiku` alias on Anthropic's own API, including for background and side tasks that use it, those requests now go to Haiku 5.5 and are priced as Haiku 5.5. On Bedrock, Vertex, Foundry, Mantle or a gateway nothing moves unless you choose the new model yourself.\n\n- Flag `tengu_idempotent_wolf`: Not enough to say (read for one account on one subscription tier against v2.1.293; this account: no value returned, anonymous baseline: no value returned, compiled default: on) These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.\n- Area: Effort\n- Tier: You'll notice\n- Useful: 5\/5\n- Signal: 4\/5\n- Scope: individual\n- Heads-up: yes"}