GPT-5 vs Grok 4.1 Fast

Head-to-head results from our 12-test suite: GPT-5 wins three distinct tests outright — tool calling (GPT-5 5 vs Grok 4; GPT-5 tied for 1st of 54, Grok ranks 18/54), agentic planning (5 vs 4; GPT-5 tied for 1st, Grok rank 16/54), and safety calibration (2 vs 1; GPT-5 rank 12/55, Grok rank 32/55). Nine tests tie at the same score: structured output (5/5, both tied for 1st), strategic analysis (5/5, both tied for 1st), constrained rewriting (4/4, both rank 6/53), creative problem solving (4/4, both rank 9/54), faithfulness (5/5, both tied for 1st), classification (4/4, both tied for 1st), long context (5/5, both tied for 1st), persona consistency (5/5, both tied for 1st), and multilingual (5/5, both tied for 1st). Practical implications: GPT-5’s 5/5 in tool calling and agentic planning (tied for top ranks) means better function selection, argument accuracy, and goal decomposition in our tests — critical for multi-step agent flows and tool integrations. Safety_calibration being higher for GPT-5 indicates it more often refuses harmful prompts while permitting legitimate ones. Both models tie on faithfulness, long-context retrieval, structured-output compliance, and multilingual capability, so for tasks requiring stable JSON output, multi-language parity, or working with 30K+ contexts they perform equivalently in our testing. External benchmarks: GPT-5 scores 73.6% on SWE-bench Verified (Epoch AI), 98.1% on MATH Level 5 (Epoch AI) — rank 1 of 14 on that test — and 91.4% on AIME 2025 (Epoch AI); Grok 4.1 Fast has no external benchmark scores in the payload. These external numbers explain GPT-5’s strength on coding/math-style problems and why it outranks many models on MATH Level 5.

Per the payload, GPT-5 charges $1.25 per mTok input and $10.00 per mTok output; Grok 4.1 Fast charges $0.20 per mTok input and $0.50 per mTok output (price ratio 20). Assuming a 50/50 split of input/output tokens: for 1M tokens/month GPT-5 ≈ $5,625 vs Grok ≈ $350; for 10M tokens/month GPT-5 ≈ $56,250 vs Grok ≈ $3,500; for 100M tokens/month GPT-5 ≈ $562,500 vs Grok ≈ $35,000. The gap matters for any high-volume deployment (chatbots, analytics pipelines, user-facing assistants). Small teams or low-volume prototypes may accept GPT-5’s premium for accuracy; anyone processing millions of tokens monthly should evaluate Grok to cut infrastructure costs by an order of magnitude.

Choose GPT-5 if you need best-in-class tool calling, agentic planning, stronger safety calibration, or top-tier math/coding performance (MATH Level 5 98.1% — Epoch AI). Choose Grok 4.1 Fast if you need a far lower cost per token (output $0.50/mk vs GPT-5 $10/mk), want the largest context window (2,000,000 tokens vs GPT-5 400,000), or are operating at scale where tens/hundreds of thousands of dollars per month matter. Specifics: pick GPT-5 for multi-step automation, high-stakes synthesis, and math/coding tasks; pick Grok 4.1 Fast for high-volume customer support, long-document retrieval, and cost-constrained production.