Claude Haiku 4.5 vs Grok 4.1 Fast

Across our 12-test benchmark suite, Claude Haiku 4.5 wins 3 categories outright, Grok 4.1 Fast wins 2, and the two models tie on 7. Neither model dominates — the choice comes down to which specific capabilities your use case demands.

Where Haiku 4.5 wins:

• Tool calling (5 vs 4): Haiku 4.5 scores 5/5, tied for 1st with 16 other models out of 54 tested. Grok 4.1 Fast scores 4/5, ranking 18th of 54. For function selection, argument accuracy, and multi-step sequencing — the backbone of agentic and API-integrated workflows — Haiku 4.5 has a concrete advantage.

• Agentic planning (5 vs 4): Haiku 4.5 scores 5/5, tied for 1st with 14 other models out of 54. Grok 4.1 Fast scores 4/5, ranking 16th. This covers goal decomposition and failure recovery — critical for autonomous agents that need to adapt mid-task.

• Safety calibration (2 vs 1): Both models score below the field median (p50 = 2), but Haiku 4.5's score of 2 ranks 12th of 55 while Grok 4.1 Fast's score of 1 ranks 32nd of 55. Neither model excels here — this is a relative win, not a strong result for either.

Where Grok 4.1 Fast wins:

• Structured output (5 vs 4): Grok 4.1 Fast scores 5/5, tied for 1st with 24 other models out of 54. Haiku 4.5 scores 4/5, ranking 26th. For JSON schema compliance and format adherence at scale — think pipelines that consume model output programmatically — Grok 4.1 Fast has an edge.

• Constrained rewriting (4 vs 3): Grok 4.1 Fast scores 4/5, ranking 6th of 53. Haiku 4.5 scores 3/5, ranking 31st of 53. This is the biggest relative gap in the dataset: compressing content within hard character limits is clearly a Grok 4.1 Fast strength.

Where they tie (7 categories):

Strategic analysis, creative problem solving, faithfulness, classification, long context, persona consistency, and multilingual all score identically. Both models hit 5/5 on long context (retrieval accuracy at 30K+ tokens), faithfulness (no hallucinations on source material), multilingual output, and persona consistency. Both score 4/5 on creative problem solving and classification. These are genuine ties — no meaningful distinction in our testing.

One infrastructure difference worth noting: Grok 4.1 Fast offers a 2,000,000-token context window versus Haiku 4.5's 200,000 tokens — a 10x advantage for workloads that need to process very long documents in a single pass. Grok 4.1 Fast also supports additional parameters including logprobs, top_logprobs, and seed, and accepts file inputs in addition to text and images. Haiku 4.5 supports top_k and stop parameters that Grok 4.1 Fast does not. Grok 4.1 Fast uses reasoning tokens (uses_reasoning_tokens quirk in the payload), which affects how reasoning-mode costs are calculated.

The price gap here is substantial and grows fast with scale. Claude Haiku 4.5 costs $1.00 per million input tokens and $5.00 per million output tokens. Grok 4.1 Fast costs $0.20 per million input tokens and $0.50 per million output tokens — 5x cheaper on input, 10x cheaper on output.

At 1M output tokens/month: Haiku 4.5 costs $5.00 vs Grok 4.1 Fast's $0.50 — a $4.50 difference, easily absorbed.

At 10M output tokens/month: $50.00 vs $5.00 — a $45 gap. Still manageable for most teams.

At 100M output tokens/month: $500.00 vs $50.00 — a $450/month difference that becomes a real budget line item.

Developers running high-throughput pipelines — customer support bots, document processors, batch summarization — should take the Grok 4.1 Fast cost advantage seriously. Haiku 4.5's edge in tool calling and agentic planning would need to translate into measurable outcome improvements to justify 10x the output spend. For low-volume or latency-sensitive use cases where a few dollars difference is irrelevant, the pricing gap matters less than capability fit.

Choose Claude Haiku 4.5 if:

• Your application depends on reliable tool calling and multi-step agentic workflows — it scores 5/5 vs Grok 4.1 Fast's 4/5 on both tool calling and agentic planning in our tests.
• You need the supported_parameters top_k or stop for fine-grained generation control.
• Safety calibration margin matters and you want the higher-ranked option between the two (rank 12 vs rank 32 of 55).
• Cost is not a primary concern at your usage volume.

Choose Grok 4.1 Fast if:

• You're running output-heavy pipelines where the 10x output cost difference ($0.50 vs $5.00 per million tokens) materially affects unit economics.
• Your pipeline consumes structured JSON output — Grok 4.1 Fast scores 5/5 vs Haiku 4.5's 4/5 on structured output in our tests.
• You need to process very long documents in a single pass — Grok 4.1 Fast's 2M-token context window is 10x Haiku 4.5's 200K.
• Content compression within tight character limits is a core task — Grok 4.1 Fast ranks 6th of 53 on constrained rewriting vs Haiku 4.5's 31st.
• Your application ingests file inputs alongside text and images.