Claude Haiku 4.5 vs GPT-5 Nano

Overview: Across our 12-test suite, Claude Haiku 4.5 wins 7 tests, GPT-5 Nano wins 2, and 3 are ties. Detailed walk-through: 1) Tool calling — Haiku 5 vs GPT-5 Nano 4. Haiku ties for 1st ("tied for 1st with 16 other models out of 54 tested"), while GPT-5 Nano is rank 18/54; expect Haiku to pick and sequence functions more accurately in multi-step tool workflows. 2) Strategic analysis — Haiku 5 vs GPT-5 Nano 4; Haiku tied for 1st of 54 (with 25 others) while GPT-5 Nano ranks 27/54; Haiku gives stronger nuanced tradeoff reasoning and numeric tradeoffs. 3) Faithfulness — Haiku 5 vs GPT-5 Nano 4; Haiku tied for 1st of 55, GPT-5 Nano rank 34/55; Haiku is less likely to invent facts in our tests. 4) Classification — Haiku 4 vs GPT-5 Nano 3; Haiku tied for 1st of 53, GPT-5 Nano rank 31/53; use Haiku where routing/labeling accuracy matters. 5) Persona consistency — Haiku 5 vs GPT-5 Nano 4; Haiku tied for 1st (36 others) while GPT-5 Nano ranks 38/53; Haiku better maintains character and resists injection. 6) Agentic planning — Haiku 5 vs GPT-5 Nano 4; Haiku tied for 1st, GPT-5 Nano rank 16/54; Haiku handles goal decomposition and recovery more robustly. 7) Creative problem solving — Haiku 4 vs GPT-5 Nano 3; Haiku ranks 9/54, GPT-5 Nano ranks 30/54—Haiku produces more feasible, specific ideas. 8) Structured output — GPT-5 Nano 5 vs Haiku 4; GPT-5 Nano tied for 1st (24 others) while Haiku ranks 26/54; GPT-5 Nano is stronger at strict JSON/schema compliance. 9) Safety calibration — GPT-5 Nano 4 vs Haiku 2; GPT-5 Nano ranks 6/55 (tied with 3) vs Haiku rank 12/55; GPT-5 Nano better balances refusal vs permissive answers in our tests. 10) Constrained rewriting — tie 3 vs 3; both rank 31/53; equal on tight character/format compression. 11) Long context — tie 5 vs 5; both tied for 1st of 55; both handle 30K+ token retrieval accurately. 12) Multilingual — tie 5 vs 5; both tied for 1st of 55; both produce equivalent quality non-English output. External math benchmarks: GPT-5 Nano posts 95.2% on MATH Level 5 and 81.1% on AIME 2025 (Epoch AI) — include these as supplementary evidence for GPT-5 Nano's math strengths. In short: Haiku leads on planning, tool use, faithfulness and classification; GPT-5 Nano leads on strict structured output and safety; both tie on long context and multilingual.

Output-price comparison (matches payload priceRatio 12.5): Claude Haiku 4.5 output = $5 per 1k tokens; GPT-5 Nano output = $0.4 per 1k tokens. At output-only volumes: 1M tokens = Haiku $5,000 vs GPT-5 Nano $400; 10M = $50,000 vs $4,000; 100M = $500,000 vs $40,000. Input costs in the payload are Haiku $1/1k and GPT-5 Nano $0.05/1k; if you assume a 1:1 input:output token ratio, combined costs per 1k are $6.00 (Haiku) vs $0.45 (GPT-5 Nano) — so 1M tokens at 1:1 becomes $6,000 vs $450. Who should care: any app with millions of tokens/month (SaaS, search/chat logs, high-volume assistants) will see tens- to hundreds-of-thousands of dollars difference; prototypes and low-volume use may prefer Haiku for higher scores, but cost-sensitive production should default to GPT-5 Nano.

Choose Claude Haiku 4.5 if you need best-in-class tool calling, strategic reasoning, faithfulness, classification and persona consistency for high-value assistant workflows and you can afford a higher per-token bill (output $5/1k). Choose GPT-5 Nano if you need the cheapest production option with top structured-output reliability and stronger safety calibration (output $0.4/1k), or if you require superior external math scores (MATH Level 5 95.2% and AIME 2025 81.1% per Epoch AI). For high-volume deployments where cost is the primary constraint, GPT-5 Nano is the pragmatic default; for tasks where subtle reasoning, tool orchestration, and factual fidelity materially impact product value, invest in Claude Haiku 4.5.