Claude Haiku 4.5: Fast, Cheap, and Surprisingly Capable

Claude Haiku 4.5 launched on October 15, 2025, as the smallest and cheapest model in the 4.5 family. Its real impact came from Claude Code's smart model switching feature, which automatically routed simple tasks to Haiku while reserving heavier models for complex work.

Key Specs

What Haiku 4.5 Brought to the Table

Haiku 4.5 was not built to replace Sonnet or Opus. It was built to handle the 30-40% of Claude Code tasks that do not require heavy reasoning, and to handle them fast and cheap.

Smart model switching. This was the headline feature. Claude Code began automatically routing simpler tasks to Haiku 4.5: file reads, quick edits, simple questions, boilerplate generation, and straightforward refactors. Users did not have to manually switch models. The system made the call.

Pro plan availability. Haiku 4.5 was added for Claude Code Pro plan users, making intelligent model routing available without API billing. This expanded the practical value of the Pro subscription significantly.

Speed. Haiku models are fast. For tasks where you are waiting for a quick answer or a simple file edit, the lower latency was noticeable. Responses that took 3-5 seconds on Sonnet came back in under 2 seconds on Haiku.

Cost reduction. For teams paying per token through the API, routing routine operations to Haiku cut daily costs substantially. The savings compounded quickly for teams running Claude Code across multiple developers.

What Haiku 4.5 Is Good At

The model handles routine development tasks well:

• File reading and summarization. Scanning a file and answering questions about its contents.
• Quick edits. Small, targeted changes to existing code.
• Simple questions. "What does this function do?" or "What's the correct import path?"
• Boilerplate generation. Creating standard patterns, test scaffolding, and configuration files.
• Commit messages and documentation. Writing clear, conventional commit messages and inline documentation.

Where Haiku 4.5 Falls Short

Know its limits. Do not rely on Haiku for:

• Complex architecture decisions. Multi-system design requires the reasoning depth of Sonnet 4.5 or Opus.
• Multi-file refactoring. Large-scale changes across many files need a model that can hold more context in its working memory.
• Deep debugging. Tracing subtle bugs through dependency chains demands stronger reasoning.
• Nuanced code review. Catching security issues, performance bottlenecks, and architectural anti-patterns requires more capability.

Smart model switching handles this routing automatically in most cases. But if you are explicitly choosing a model for a complex task, reach for Sonnet or Opus.

How It Compared to Previous Haiku Models

Haiku 4.5 was a significant step up from earlier Haiku releases. Previous Haiku models felt like a different class of tool entirely. Haiku 4.5 closed the gap enough that for simple tasks, most users could not tell the difference between Haiku output and Sonnet output.

The quality floor rose substantially. Earlier Haiku models would occasionally produce obviously wrong or incomplete code. Haiku 4.5 made those failures rare for its intended use cases.

Current Status

Haiku 4.5 remains active and is the current Haiku model available in Claude Code. It is accessible via the haiku alias or its full model ID.

Related Pages

• All Claude Models for the complete model timeline
• Sonnet 4.5 for the mid-tier daily driver
• Opus 4.5 for the top-tier reasoning model
• Model selection guide for strategic model switching
• Usage optimization for managing Claude Code costs