DeepSeek V3.1 Terminus vs GPT-4.1

Summary of the 12-test comparison (scores are our 1–5 ratings unless noted):

• Tool calling: GPT-4.1 5 vs DeepSeek 3 — GPT-4.1 wins and ranks tied for 1st of 54 models on tool calling; expect better function selection, argument accuracy and sequencing in real workflows.
• Faithfulness: GPT-4.1 5 vs DeepSeek 3 — GPT-4.1 ties for 1st of 55 on faithfulness; better at sticking to source material and avoiding hallucinations.
• Classification: GPT-4.1 4 vs DeepSeek 3 — GPT-4.1 ties for 1st of 53; more reliable routing and categorization.
• Persona consistency: GPT-4.1 5 vs DeepSeek 4 — GPT-4.1 ties for 1st of 53, so it holds character and resists injection better in our tests.
• Constrained rewriting: GPT-4.1 5 vs DeepSeek 3 — GPT-4.1 ties for 1st of 53, so it's stronger at compressing content within hard limits.
• Structured output: DeepSeek 5 vs GPT-4.1 4 — DeepSeek ties for 1st of 54 on JSON/schema compliance; better when strict schema adherence is required.
• Creative problem solving: DeepSeek 4 vs GPT-4.1 3 — DeepSeek ranks 9 of 54, giving more specific, feasible ideas in our tasks.
• Strategic analysis: tie (both 5) — both tied for 1st on nuanced tradeoff reasoning.
• Long context: tie (both 5) — both tied for 1st on retrieval across 30K+ tokens. GPT-4.1 additionally lists a 1,047,576 token context window in the payload.
• Agentic planning: tie (both 4) — both rank 16 of 54; comparable goal decomposition and recovery.
• Multilingual: tie (both 5) — both tied for 1st of 55.
• Safety calibration: tie (both 1) — both rank 32 of 55, indicating conservative or limited safety calibration in our tests. External benchmarks (Epoch AI): GPT-4.1 scored 48.5% on SWE-bench Verified, 83% on MATH Level 5, and 38.3% on AIME 2025; these are Epoch AI results and supplemental to our internal scores. DeepSeek has no external benchmark scores in the payload. In short, GPT-4.1 dominates tool-oriented, faithfulness-sensitive, and classification tasks; DeepSeek leads when strict structured output and idea generation matter, and it does so at ~10% of GPT-4.1's per-token price.

Per the payload, DeepSeek V3.1 Terminus charges $0.21 input + $0.79 output per mTok (combined $1.00/mTok). GPT-4.1 charges $2 input + $8 output per mTok (combined $10.00/mTok). Assuming 'per mTok' = per 1,000 tokens, monthly costs are: 1M tokens — DeepSeek $1,000 vs GPT-4.1 $10,000; 10M tokens — DeepSeek $10,000 vs GPT-4.1 $100,000; 100M tokens — DeepSeek $100,000 vs GPT-4.1 $1,000,000. Teams building at millions+ tokens/month (SaaS, large-scale assistants, chat archives) will feel the GPT-4.1 premium acutely; smaller projects or budget-constrained integrations will prefer DeepSeek for a roughly 10x lower per-token bill while accepting tradeoffs in tool calling and faithfulness.

Choose DeepSeek V3.1 Terminus if: you need the cheapest option at scale (≈$1,000 per 1M tokens), require top-tier structured output/JSON compliance, or prioritize creative ideation and schema fidelity. Choose GPT-4.1 if: you require best-in-class tool calling, higher faithfulness and persona consistency, accurate classification, or multimodal inputs (payload lists text+image+file→text); accept the ~10x higher per-token cost for those gains.