Claude Haiku 4.5 vs GPT-5.1

Summary of our 12-test suite (scores 1–5) and ranks shown in the payload: - Tool calling: Claude Haiku 4.5 scores 5 vs GPT‑5.1’s 4; Haiku is tied for 1st on tool_calling in our testing, while GPT‑5.1 ranks 18th of 54. This matters for systems that must pick functions, pass correct args, and sequence tool calls. - Agentic planning: Haiku 5 vs GPT‑5.1 4; Haiku is tied for 1st on agentic_planning (useful for goal decomposition and recovery). - Constrained rewriting: GPT‑5.1 wins 4 vs Haiku 3; GPT‑5.1 ranks 6th of 53 here, so it’s stronger when you need tight character/byte compression and exactness. - Faithfulness, long_context, persona_consistency, multilingual, classification, strategic_analysis, creative_problem_solving: ties (both models hit top scores in many of these). Both score 5 on faithfulness and long_context and rank tied for 1st in those categories — so both are reliable on retrieval over 30k+ tokens and sticking to source material in our tests. - Structured output: tie at 4; both rank 26 of ~54, meaning JSON/schema compliance is comparable. - Safety calibration: both score 2 and rank 12 of 55, so neither is a standout on delicate refusal tuning in our tests. External benchmarks (Epoch AI): GPT‑5.1 scores 68% on SWE-bench Verified and 88.6% on AIME 2025; we reference these as supplementary evidence of GPT‑5.1’s strengths on coding problem resolution and contest math. Claude Haiku 4.5 has no external SWE-bench/AIME scores in the payload. Overall: in our testing Haiku wins tool-calling and agentic planning (and ranks tied for 1st in several categories); GPT‑5.1 wins constrained rewriting and brings higher external math/coding scores.

Raw per‑million-token pricing from the payload: Claude Haiku 4.5 charges $1 input / $5 output per million tokens; GPT-5.1 charges $1.25 input / $10 output per million tokens. If your traffic is 50/50 input/output, Haiku costs $3.00 per million tokens versus GPT‑5.1 at $5.625 per million. At monthly volumes this looks like: 1M tokens → $3.00 vs $5.63; 10M → $30.00 vs $56.25; 100M → $300.00 vs $562.50. If your workload is output-heavy (e.g., long generations), the gap widens: Haiku output-only = $5/M; GPT‑5.1 output-only = $10/M. Teams running high-volume chat, summarization, or large-scale agent fleets should care about the difference; smaller apps or research projects may prioritize GPT‑5.1’s external benchmark strengths despite the higher cost.

Choose Claude Haiku 4.5 if you need cost-efficient production at scale, stronger tool-calling and agentic planning (Haiku = 5 vs GPT‑5.1 = 4), and a low output price ($5/M). Choose GPT‑5.1 if you require better constrained rewriting (4 vs 3), the largest context/window (400k tokens vs 200k), or external coding/math performance evidence (SWE-bench 68%, AIME 2025 88.6% per Epoch AI) and you can absorb roughly double the output cost.