Claude Haiku 4.5 vs Sonnet 5 for production automation.

Haiku 4.5 should be tested more often. Teams frequently default to a larger model without checking whether a fast bounded task actually needs it. At scale, that assumption becomes a recurring cost and latency penalty.

Sonnet 5 remains the stronger default when work requires planning, complex reasoning, coding, a large context window, or flexible tool use. The right architecture may use both.

Source note: Specifications come from Anthropic's current model overview and official Haiku 4.5 and Sonnet 5 announcements.

Haiku 4.5 vs Sonnet 5 specifications

Choose Haiku for bounded volume

Good candidates have clear inputs, narrow outputs, deterministic validation, and frequent repetition. Examples include classification, extraction, intent routing, summarization, metadata generation, lightweight support, simple tool calls, and parallel sub-agent tasks.

Haiku's lower latency improves interactive response and tool loops. Its base token cost is half Sonnet's introductory cost and one-third of the announced standard cost. That difference is meaningful at millions of requests, but only if output passes validation.

Choose Sonnet for complexity

Sonnet is better suited when the model must plan, combine many sources, write or reason about code, handle ambiguous requests, call tools across multiple steps, interpret difficult visual inputs, or maintain coherence over a large context.

The 1M context window also supports workloads that cannot fit inside Haiku's 200k limit. Do not treat context capacity as a reason to send every available document; retrieval and context design still affect quality, latency, and cost.

Use Haiku and Sonnet together

A tiered design can classify or process normal cases with Haiku, then escalate validation failures or difficult cases to Sonnet. Haiku can also execute parallel subtasks under a Sonnet orchestrator. This is valuable when the orchestrator needs stronger planning but individual tasks are simple and numerous.

Define escalation with evidence: schema validation failure, missing required facts, conflicting sources, low confidence from an external verifier, high-risk intent, or a task class known to underperform on Haiku. Do not let the model's unsupported self-confidence decide alone.

Cost example

For 20 million input tokens and 5 million output tokens, Haiku's base monthly cost is $45. Sonnet's introductory cost is $90, rising to $135 at announced standard pricing. If Sonnet increases accepted completion enough to save more than $45-$90 in review and rework, it is already the cheaper workflow.

Calculate a different workload with the Claude API cost calculator.

Evaluation plan

1. Separate routine cases from difficult and high-risk cases.
2. Define validation that does not rely only on another model's opinion.
3. Run Haiku and Sonnet on the same representative set.
4. Measure accepted completion, latency, token use, retries, and reviewer time.
5. Test a routed design against single-model baselines.
6. Choose the simplest configuration that meets quality and risk requirements.

Frequently asked questions