GPT-5.4 vs Grok 4.1 Fast

Across our 12-test internal benchmark suite, GPT-5.4 wins 2 tests outright, Grok 4.1 Fast wins 1, and the two models tie on 9.

Where GPT-5.4 wins:

• Safety calibration: 5 vs 1. This is the most decisive gap in the entire comparison. GPT-5.4 ranks tied for 1st among 5 models out of 55 tested; Grok 4.1 Fast ranks 32nd of 55 in our testing. For any deployment that needs to refuse harmful requests reliably while permitting legitimate ones, this is a disqualifying gap for Grok 4.1 Fast.
• Agentic planning: 5 vs 4. GPT-5.4 ties for 1st among 15 models out of 54; Grok 4.1 Fast ranks 16th of 54 (tied with 25 others). Goal decomposition and failure recovery — the core of autonomous agent workflows — skews toward GPT-5.4 here.

Where Grok 4.1 Fast wins:

• Classification: 4 vs 3. Grok 4.1 Fast ties for 1st among 30 models out of 53 tested; GPT-5.4 ranks 31st of 53. For routing, categorization, and tagging tasks, Grok 4.1 Fast has a measurable edge in our testing.

Where they tie (9 tests): Both models score identically on structured output (5/5), strategic analysis (5/5), faithfulness (5/5), long context (5/5), persona consistency (5/5), and multilingual (5/5) — all at or near the top of our rankings. They also match on constrained rewriting (4/4), creative problem solving (4/4), and tool calling (4/4).

On external benchmarks (Epoch AI data), GPT-5.4 scores 76.9% on SWE-bench Verified (rank 2 of 12 models tested) and 95.3% on AIME 2025 (rank 3 of 23). SWE-bench Verified tests real GitHub issue resolution — GPT-5.4's 76.9% exceeds the median of 70.8% across models with scores in our dataset, placing it solidly in the top tier for autonomous coding tasks. Its AIME 2025 score of 95.3% sits well above the dataset median of 83.9%, indicating strong competition-level math reasoning. Grok 4.1 Fast has no external benchmark scores in our dataset, so no direct comparison is possible on those dimensions.

The price gap here is not a rounding error — it is a 30x difference on output tokens. GPT-5.4 costs $2.50/M input and $15.00/M output. Grok 4.1 Fast costs $0.20/M input and $0.50/M output.

At 1M output tokens/month: GPT-5.4 costs $15 vs Grok 4.1 Fast's $0.50 — a $14.50 difference that barely registers.

At 10M output tokens/month: $150 vs $5 — a $145 gap that starts to matter for lean teams.

At 100M output tokens/month: $1,500 vs $50 — a $1,450 monthly delta that becomes a line item in any serious API budget.

Who should care: Any developer running customer support bots, document processing pipelines, or high-frequency chat applications will find Grok 4.1 Fast's pricing transformative. For low-volume internal tools, research assistants, or applications where safety calibration is non-negotiable, the GPT-5.4 premium is easier to justify. Note also that Grok 4.1 Fast uses reasoning tokens (a quirk flagged in its parameters), which can inflate actual output token counts if reasoning is enabled — factor that into volume estimates.

Choose GPT-5.4 if:

• Safety calibration is a hard requirement — its score of 5 vs Grok 4.1 Fast's 1 in our testing represents a fundamental capability difference, not a marginal one.
• You are building autonomous agents that require reliable goal decomposition and failure recovery (agentic planning score of 5 vs 4).
• You need strong coding performance backed by external evidence: 76.9% on SWE-bench Verified (Epoch AI) puts it in the top tier for real-world code tasks.
• Volume is low-to-moderate and the $15/M output token cost is manageable against quality requirements.
• You need a 1M+ token context window (GPT-5.4 supports up to 1,050,000 tokens).

Choose Grok 4.1 Fast if:

• You are running high-volume workloads where $0.50/M output tokens vs $15/M is a real budget constraint — at 100M tokens/month, you save $1,450.
• Your application centers on classification and routing tasks, where Grok 4.1 Fast outscores GPT-5.4 (4 vs 3) in our testing.
• Safety calibration is not a critical requirement for your use case.
• You need a 2M token context window — Grok 4.1 Fast's window is nearly double GPT-5.4's.
• You want optional reasoning token support (togglable via parameters) for tasks that benefit from chain-of-thought without committing to it globally.
• xAI's description of Grok 4.1 Fast as optimized for customer support and deep research aligns with your workload.