GPT-4o-mini vs GPT-5.1

Overview (in our 12-test suite): GPT-5.1 wins 8 tests, GPT-4o-mini wins 1, and 3 are ties. Details (scores are from our testing unless noted):

• Multilingual: GPT-5.1 = 5 vs GPT-4o-mini = 4. GPT-5.1 ties for 1st in our rankings (tied with 34 others out of 55), so expect better parity across non-English tasks with GPT-5.1.
• Creative problem solving: GPT-5.1 = 4 vs GPT-4o-mini = 2; GPT-5.1 ranks 9 of 54 vs GPT-4o-mini at 47 of 54, so GPT-5.1 will generate more feasible, non-obvious ideas in problem-solving prompts.
• Constrained rewriting: GPT-5.1 = 4 vs GPT-4o-mini = 3; GPT-5.1 ranks 6 of 53, indicating tighter adherence to hard-length constraints.
• Faithfulness: GPT-5.1 = 5 vs GPT-4o-mini = 3; GPT-5.1 is tied for 1st in faithfulness (tied with 32 others), meaning fewer hallucinations and better stick-to-source behavior in our tests.
• Long context: GPT-5.1 = 5 vs GPT-4o-mini = 4; GPT-5.1 is tied for 1st in long context, which matters for retrieval and summarization at 30k+ tokens.
• Persona consistency: GPT-5.1 = 5 vs GPT-4o-mini = 4; GPT-5.1 ties for top ranks here, so it better maintains character and resists injection in multi-turn scenarios.
• Agentic planning & strategic analysis: GPT-5.1 scores 4/5 in agentic planning and 5 in strategic analysis vs GPT-4o-mini's 3 and 2 respectively — GPT-5.1 is clearly superior at goal decomposition and nuanced tradeoff reasoning.
• Tool calling: both score 4 (tie); both models perform similarly on function selection and sequencing in our tests.
• Structured output & classification: ties at 4; GPT-4o-mini is tied for 1st in classification with 29 others, and GPT-5.1 shares that top rank as well — both are adequate for schema-driven outputs.
• Safety calibration: GPT-4o-mini = 4 vs GPT-5.1 = 2 (GPT-4o-mini ranks 6 of 55 on safety calibration). If safe refusals with correct allow/deny behavior are critical, GPT-4o-mini performed better in our suite. External benchmarks (Epoch AI): GPT-5.1 scores 68% on SWE-bench Verified and 88.6% on AIME 2025 (Epoch AI). GPT-4o-mini scored 52.6% on MATH Level 5 and 6.9% on AIME 2025 in the payload (Epoch AI). These external results corroborate GPT-5.1's superiority on math and coding-style tests.

Prices (per payload): GPT-4o-mini input $0.15 per 1k tokens, output $0.60 per 1k; GPT-5.1 input $1.25 per 1k, output $10.00 per 1k. Interpreting at scale (assumes 1:1 input:output token volumes):

• 1M input + 1M output tokens/month: GPT-4o-mini = $750 ( $150 input + $600 output ); GPT-5.1 = $11,250 ( $1,250 input + $10,000 output ).
• 10M input + 10M output: GPT-4o-mini = $7,500; GPT-5.1 = $112,500.
• 100M input + 100M output: GPT-4o-mini = $75,000; GPT-5.1 = $1,125,000. The payload's priceRatio (0.06) reflects output-cost parity: GPT-4o-mini output is ~6% of GPT-5.1's output price. Who should care: startups, high-volume chat apps, and any cost-sensitive production pipelines should prefer GPT-4o-mini; R&D teams, research labs, or products that require state-of-the-art reasoning, math, or the longest context windows may justify GPT-5.1's much higher hourly/throughput cost.

Choose GPT-4o-mini if: you need a low-cost production model for chat, classification, or image->text; you must prioritize safety calibration and drastically reduce monthly inference costs (input $0.15/1k, output $0.60/1k). Choose GPT-5.1 if: your product requires the best reasoning, math, long-context retrieval, multilingual parity, or persona consistency and you can absorb much higher inference costs (input $1.25/1k, output $10/1k).