GPT-5 vs Claude Haiku 4.5 for legal writing: which is better in 2026?

A head-to-head look at GPT-5 and Claude Haiku 4.5 for legal writing. Benchmarks via artificialanalysis.ai, pricing as of May 2026. Compare AI models like these inside Admix.

Quick verdict

For legal writing in May 2026, Claude Haiku 4.5 edges out GPT-5 on the contextWindow metric. Cheap Claude quality for everyday tasks.

Side-by-side specs

Spec	GPT-5	Haiku
Intelligence index	78.4	65.8
Coding index	76.1	66.2
Context window	400K tokens	500K tokens
Speed (tok/s)	142	205
Input $/M	$5.00	$0.80
Output $/M	$20.00	$4.00
Released	Aug 7, 2025	Mar 19, 2026

How they handle legal writing

GPT-5: Top reasoning and math scores. The main caveat is more expensive than mid-tier models.

Claude Haiku 4.5: Cheap Claude quality for everyday tasks. The main caveat is not as strong as opus on agentic coding.

Cost per 1,000 queries

Assuming 1,500 input and 800 output tokens per query:

GPT-5: $23.50 per 1,000 queries
Claude Haiku 4.5: $4.40 per 1,000 queries

Verdict by sub-task

Best raw quality on legal writing:
Best price: Claude Haiku 4.5
Longest context: Claude Haiku 4.5
Fastest: Claude Haiku 4.5

FAQ

Is GPT-5 better than Claude Haiku 4.5 for legal writing?

On May 2026 benchmarks (artificialanalysis.ai), Claude Haiku 4.5 ranks higher than GPT-5 for legal writing on the contextWindow metric. The gap is small enough that the choice often comes down to price, context length, and tone.

Which is cheaper, GPT-5 or Claude Haiku 4.5?

GPT-5 costs $5.00 input and $20.00 output per million tokens. Claude Haiku 4.5 costs $0.80 input and $4.00 output per million tokens.

Can I use both GPT-5 and Haiku in one app?

Yes. Admix is a multi model AI chat aggregator that lets you run GPT-5 and Claude Haiku 4.5 side by side under one subscription.

Sources

Benchmarks from artificialanalysis.ai (May 2026).

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