DeepSeek V3.1 vs GPT-5.1

Overview: In our 12-test suite GPT-5.1 wins 6 tests, DeepSeek V3.1 wins 2, and 4 are ties. Faithfulness: tie at 5/5 (both tied for 1st among 55 models) — both stick to source material. Structured output (JSON/schema): DeepSeek 5 vs GPT-5.1 4 — DeepSeek tied for 1st (best-in-class for schema compliance) while GPT-5.1 ranks 26/54, so prefer DeepSeek when strict format adherence is required. Creative problem solving: DeepSeek 5 vs GPT-5.1 4 — DeepSeek tied for 1st; expect more non-obvious, feasible ideas from DeepSeek in our tests. Strategic analysis: GPT-5.1 5 vs DeepSeek 4 — GPT-5.1 ties for 1st (best at nuanced tradeoff reasoning with numbers). Constrained rewriting: GPT-5.1 4 vs DeepSeek 3 — GPT-5.1 ranks 6/53 vs DeepSeek 31/53, so GPT-5.1 is substantially better at aggressive compression under hard limits. Tool calling: GPT-5.1 4 vs DeepSeek 3 — GPT-5.1 ranks 18/54 vs DeepSeek 47/54; GPT-5.1 is measurably more reliable at function selection, argument accuracy, and sequencing. Classification: GPT-5.1 4 vs DeepSeek 3 — GPT-5.1 tied for 1st (strong routing/categorization). Safety calibration: GPT-5.1 2 vs DeepSeek 1 — GPT-5.1 ranks 12/55 (still modest), DeepSeek ranks 32/55; GPT-5.1 better at refusing harmful requests while permitting legitimate ones. Long context: tie at 5/5 and both tied for 1st — both handle 30K+ retrieval tasks in our tests, though GPT-5.1 exposes a 400,000-token window vs DeepSeek’s 32,768 tokens (useful for extremely large inputs). Persona consistency and agentic planning: ties (both strong). External benchmarks: GPT-5.1 scores 68% on SWE-bench Verified and 88.6% on AIME 2025 (Epoch AI); these external results further support GPT-5.1’s coding and math strengths. Practical meaning: pick GPT-5.1 when your product needs top classification, tool integration, constrained rewriting, multilingual support, or the largest context windows; pick DeepSeek when you need perfect schema output, high creativity for ideation, and much lower cost.

Cost per mTok (1,000 tokens): DeepSeek V3.1 — input $0.15, output $0.75. GPT-5.1 — input $1.25, output $10.00. Per 1M tokens (1,000 mTok): DeepSeek input $150 + output $750 = $900 total; GPT-5.1 input $1,250 + output $10,000 = $11,250 total. Per 10M tokens multiply by 10: DeepSeek $9,000 vs GPT-5.1 $112,500. Per 100M tokens multiply by 100: DeepSeek $90,000 vs GPT-5.1 $1,125,000. GPT-5.1 charges ~8.3x more on input and ~13.3x more on output per mTok. Who should care: high-volume deployments, startups, and cost-sensitive SaaS should strongly consider DeepSeek for price; organizations that need the specific benchmark wins (classification, tool-calling, constrained rewriting, multilingual, safety calibration, strategic analysis) may justify GPT-5.1’s higher bill.

Choose DeepSeek V3.1 if you need: - Strict structured output / JSON schema compliance (DeepSeek 5 vs GPT-5.1 4). - High creative problem solving and ideation (DeepSeek 5). - Much lower runtime cost (DeepSeek output $0.75/mTok vs GPT-5.1 $10/mTok) for high-volume deployments. Choose GPT-5.1 if you need: - Best classification, constrained rewriting, tool calling, strategic analysis, or multilingual support (GPT-5.1 wins these benchmarks). - Very large context windows and multimodal inputs (GPT-5.1 context 400,000 tokens, modality includes images/files). - External benchmark strength in coding/math (SWE-bench 68% and AIME 2025 88.6% per Epoch AI).