Claude Haiku 4.5 vs Gemini 2.5 Flash Lite for Constrained Rewriting

Constrained Rewriting (compression within hard character limits) demands precise length control, faithfulness to source meaning, predictable structured output, and robust handling of edge cases in long documents. Key capabilities: 1) constraint adherence (truncate/preserve semantics to meet hard limits), 2) faithfulness (avoid hallucination while compressing), 3) structured_output and format compliance (JSON or exact-length outputs), 4) handling long context so the model can locate and compress key passages, and 5) predictable refusal/safety behavior when asked to compress disallowed content. In our data there is no external benchmark for this task, so the primary signal is the internal constrained_rewriting score: Gemini 2.5 Flash Lite 4/5 vs Claude Haiku 4.5 3/5. Supporting scores explain the result: both models tie on faithfulness (5) and structured_output (4), so accuracy and format adherence are comparable; Gemini's higher constrained_rewriting score and its rank (6/52 vs 31/52) indicate better practical compression behavior under hard limits. Claude Haiku 4.5 provides stronger strategic_analysis (5 vs 3) and agentic_planning (5 vs 4), which can help for multi-step rewrite strategies but did not translate into a higher constrained_rewriting score in our tests.

1. Social media character trimming (tight, single-paragraph compressions): Gemini 2.5 Flash Lite (constrained_rewriting 4 vs 3) produces shorter, more reliable rewrites that meet exact character caps; choose Gemini when strict length compliance is required. 2) Enterprise SMS/notification compression where fidelity matters: both models tie on faithfulness (5), so either preserves meaning, but Gemini is more likely to hit the character limit without manual edits. 3) Multi-pass editorial compression (decompose, compress, refine): Claude Haiku 4.5 scores higher at strategic_analysis (5 vs 3) and agentic_planning (5 vs 4), so it can be better when you want the model to propose multi-step compression strategies before applying them, despite scoring lower on the single-step constrained_rewriting metric. 4) Very long documents requiring context awareness: both report long_context 5, but Gemini's context_window is 1,048,576 tokens vs Claude's 200,000 tokens — Gemini can keep more source context inline while compressing. 5) Cost-sensitive bulk rewrites: Gemini costs $0.1/$0.4 per mTok (input/output) vs Claude's $1/$5 per mTok; in production pipelines Gemini is far more cost-efficient for mass constrained rewriting tasks.

For Constrained Rewriting, choose Gemini 2.5 Flash Lite if you need reliable, low-cost compression that hits strict character limits (scores 4 vs 3; ranks 6/52 vs 31/52; much lower per-token cost). Choose Claude Haiku 4.5 if your workflow benefits from stronger strategic analysis or multi-step, planner-driven rewrite strategies despite a lower single-pass constrained_rewriting score.