GPT-5.4 vs Grok 4 for Constrained Rewriting

Constrained Rewriting demands: (1) exact compression that preserves meaning under hard character limits, (2) strict adherence to output formats or schemas, (3) inventive rephrasing to squeeze content without losing nuance, and (4) stability when given long source context. Our task definition is “Compression within hard character limits.” External benchmarks are not present for this task in the payload, so we base the primary verdict on our internal scores. Both models score 4/5 on constrained rewriting in our 12-test suite (tie). To break the tie we examine supporting capabilities: structured output (JSON/schema compliance) and creative problem solving (finding non-obvious compressions) are most relevant. GPT-5.4: structured output 5, creative problem solving 4, long context 5, faithfulness 5. Grok 4: structured output 4, creative problem solving 3, long context 5, faithfulness 5. GPT-5.4 also offers a much larger context_window (1,050,000 tokens vs Grok 4’s 256,000) and slightly lower input cost (2.5 vs 3 per mTOK), which helps when source texts are extremely long or when you need to include more instructions alongside content.

1. Tight social copy rewrite (280 chars): Both models produce acceptable rewrites (task score 4/5). GPT-5.4 is likely to better meet a strict JSON output requirement thanks to structured output 5 vs Grok 4's 4, so it will more reliably deliver a 280-char field that validates against a schema. 2) Legal clause compression preserving mandatory terms: Both tie on constrained rewriting and faithfulness (5/5), but GPT-5.4’s stronger creative problem solving (4 vs 3) helps it find compact legal phrasings while retaining required wording. 3) Batch rewrite pipeline with classification routing: Grok 4 wins classification (score 4 vs GPT-5.4's 3), so if your pipeline must auto-route by type before rewriting, Grok 4 may reduce pre-processing work. 4) Very long source documents requiring selective compression: GPT-5.4’s 1,050,000 token context window (vs 256,000) makes it preferable when the content to compress exceeds typical context limits or when you must include extensive style constraints and examples in the prompt. 5) Safety-sensitive rewrites (illicit or harmful content): GPT-5.4 scores 5/5 on safety calibration vs Grok 4’s 2/5 in our tests, so GPT-5.4 is more consistent at rejecting or sanitizing disallowed transformations when needed.

For Constrained Rewriting, choose GPT-5.4 if you require reliable schema-compliant outputs, stronger inventive compression, very large-context inputs, or tighter safety behavior. Choose Grok 4 if you need equally capable constrained rewrites but prefer better built-in classification routing or XAI-aligned tooling; Grok 4 is a close alternative (both score 4/5 on the core task).