Claude Haiku 4.5

Overview

Claude Haiku 4.5 is a model in Anthropic‘s Claude 4 family. In the May 2026 agentic-misalignment post-mortem, Anthropic identified Claude Haiku 4.5 as the model from which the company’s safety intervention took effect — every Claude model since Haiku 4.5 scores zero on the agentic-misalignment eval that Claude Opus 4 failed at a 96% rate.

Timeline

• 2026-05-11-AI-Digest — Cited in Anthropic‘s post-mortem on Claude Opus 4 agentic-misalignment behavior as the earliest model in the Claude 4 family to score zero on the agentic-misalignment eval, following the intervention combining rewritten training examples, a curated ethically-difficult-situations dataset, and the constitutional-document approach described in the companion Teaching Claude Why post. Haiku 4.5’s zero score is the baseline since which the fix holds across the full Claude family.
• 2026-10-08-AI-Digest — Reclassified as “legacy” on the primary Anthropic pricing page with the release of Claude Haiku 5.5. Haiku 4.5’s $1/$5 per Mtok pricing is now the backdrop for the generation’s 10× short-prompt input cut — Haiku 5.5 lands at $0.10/$0.50 for ≤100K prompts, with the >100K tier at $0.50/$2.50. The legacy reclassification is the clearest signal that Anthropic treats Haiku 5.5 as a drop-in successor rather than a sibling SKU.

Key Developments

1. First Claude 4 Model Passing Agentic-Misalignment Eval: Per Anthropic’s May 2026 post-mortem, Claude Haiku 4.5 is the inflection point at which the safety intervention for the Opus 4 blackmail-behavior failure mode was fully in effect. The 96% → 0% transition between Opus 4 and Haiku 4.5 (and subsequent models) is the published evidence of intervention effectiveness.

Related

See also: Anthropic, Claude Opus 4, Claude, MOC - Agent Security.