GPT-5.4 Mini vs Grok 4.1 Fast

Across our 12-test benchmark suite, GPT-5.4 Mini and Grok 4.1 Fast produce identical scores on 11 tests and differ on only one. Here's the breakdown:

Where they tie (11/12 tests):

• Structured output (5/5): Both tied for 1st among 54 models tested — reliable JSON schema compliance and format adherence.
• Classification (4/5): Both tied for 1st among 53 models — accurate categorization suitable for routing and labeling pipelines.
• Long context (5/5): Both tied for 1st among 55 models — strong retrieval accuracy at 30K+ tokens. Notably, Grok 4.1 Fast offers a 2M token context window vs GPT-5.4 Mini's 400K, which matters for truly large document ingestion even though both score identically on our 30K+ retrieval test.
• Faithfulness (5/5): Both tied for 1st among 55 models — neither hallucinates away from source material in our tests.
• Strategic analysis (5/5): Both tied for 1st among 54 models — nuanced tradeoff reasoning with real numbers.
• Persona consistency (5/5): Both tied for 1st among 53 models — maintains character and resists prompt injection.
• Multilingual (5/5): Both tied for 1st among 55 models — equivalent output quality in non-English languages.
• Constrained rewriting (4/5): Both rank 6 of 53, tied with 25 models — solid compression within hard character limits.
• Creative problem solving (4/5): Both rank 9 of 54, tied with 21 models — above median but not at the ceiling.
• Tool calling (4/5): Both rank 18 of 54, tied with 29 models — competent function selection and argument accuracy, though 17 models score higher.
• Agentic planning (4/5): Both rank 16 of 54, tied with 26 models — solid goal decomposition, not top-tier.

Where they differ (1/12 tests):

• Safety calibration: GPT-5.4 Mini scores 2/5 (rank 12 of 55); Grok 4.1 Fast scores 1/5 (rank 32 of 55). Neither model excels here — the field median is 2/5 — but GPT-5.4 Mini is measurably more accurate at refusing harmful requests while permitting legitimate ones. For applications where content policy compliance is auditable and critical, this single-point gap carries real weight.

The practical takeaway: benchmark parity is near-total. The context window difference (2M vs 400K) and the safety calibration gap are the only functional differentiators beyond price.

The 9x output cost gap is the defining factor in this comparison. GPT-5.4 Mini charges $4.50 per million output tokens; Grok 4.1 Fast charges $0.50. At 1M output tokens/month, that's $4.50 vs $0.50 — a $4 difference that's easy to ignore. At 10M output tokens/month, the gap widens to $45 vs $5, saving $40/month with Grok 4.1 Fast. At 100M output tokens/month — realistic for customer support pipelines, document processing, or high-volume API products — you're looking at $450 vs $50, a $400/month difference that adds up to nearly $5,000/year. Input costs follow a similar but smaller ratio: $0.75 vs $0.20 per MTok, so read-heavy workloads with short outputs still favor Grok 4.1 Fast by 3.75x. Developers running cost-sensitive, high-throughput workloads should treat Grok 4.1 Fast as the default unless a specific GPT-5.4 Mini capability is required. Note that Grok 4.1 Fast uses reasoning tokens (enabled/disabled via API), which can affect output token consumption if reasoning is left on for simple tasks.

Choose GPT-5.4 Mini if: safety calibration is a hard requirement for your use case — it scores 2/5 vs Grok 4.1 Fast's 1/5 in our testing, and for regulated industries or consumer-facing products with content moderation obligations, that gap matters. Also consider it if you're already deeply integrated into OpenAI's API ecosystem and switching costs outweigh the price savings.

Choose Grok 4.1 Fast if: you're optimizing for cost at any meaningful scale — the $0.50 vs $4.50 per MTok output cost means 9x savings that compound dramatically at 10M+ tokens/month. It also offers a 2M token context window (vs 400K), making it the better fit for applications that need to ingest very large documents or long conversation histories. For customer support pipelines, deep research agents, and high-throughput batch workloads where safety calibration isn't the primary constraint, Grok 4.1 Fast delivers identical benchmark performance at a fraction of the cost.