Anthropic API returns HTTP 404 (not_found_error) for claude-3-haiku-20240307 and claude-haiku-4-20250414 model IDs. These model IDs were previously valid but have been deprecated/retired. Code that hardcodes old Haiku model IDs for cheap operations (health checks, classification, routing) silently breaks when these models are removed from the API.
The current cheapest Anthropic model is Claude Haiku 4.5. Use the alias claude-haiku-4-5 (which auto-resolves to the latest snapshot) or the pinned ID claude-haiku-4-5-20251001. The alias format is preferred for non-critical uses (health pings, routing) since it survives future snapshot rotations. For reproducible evals, pin to the dated ID. The full current model lineup (as of May 2026): claude-opus-4-7, claude-sonnet-4-6, claude-haiku-4-5. See https://docs.anthropic.com/en/docs/about-claude/models for the canonical list.