Claude Haiku 4.5 vs DeepSeek V3.1 for Constrained Rewriting

What Constrained Rewriting demands: precise compression to meet hard character/token limits while retaining meaning and required structure. Key capabilities: (1) structured_output (format/length adherence), (2) faithfulness (stays true to source), (3) reliable token/char control or tool integrations for exact enforcement, and (4) sufficient context to identify what must be preserved. External benchmark: none provided for this task in the payload, so our winner call relies on internal task scores and supporting proxies. Both models scored 3/5 on our constrained_rewriting test and share rank 31 of 52; therefore supporting metrics decide the edge. DeepSeek V3.1: structured_output 5, creative_problem_solving 5, tool_calling 3, long_context 5, faithfulness 5. Claude Haiku 4.5: structured_output 4, tool_calling 5, long_context 5 (200k window), faithfulness 5. For strict format/char compliance and cost-sensitive batch workflows, structured_output and lower output cost weigh heavier. For very large-context compression tasks or programmatic enforcement (tooling), Haiku’s tool_calling and massive context window provide advantages.

1. High-volume SMS/Twitter-style rewriting (many short outputs with strict char limits): DeepSeek V3.1 is preferable — both models scored 3/5 on the constrained task, but DeepSeek’s structured_output 5 vs Haiku’s 4 and its lower output cost ($0.75 vs $5.00 per mTok) reduce error and cut cost. 2) Single-document micro-summary where you must preserve precise clauses from a 50k+ token source: Claude Haiku 4.5 is preferable because of its 200,000-token context window and tool_calling 5, which help retain context and enforce exact-length rules programmatically. 3) Template-driven deliveries (JSON/CSV with exact fields and char caps): DeepSeek V3.1’s structured_output 5 makes it less likely to violate schemas; Haiku can match this when paired with tools but at higher per-output cost. 4) Creative compression where rephrasing choices matter (tradeoffs between terseness and fidelity): DeepSeek’s creative_problem_solving 5 gives it an edge producing non-obvious compressions while staying faithful (both have faithfulness 5).

For Constrained Rewriting, choose DeepSeek V3.1 if your priority is exact format compliance and cost-efficiency at scale (structured_output 5; $0.75 per mTok). Choose Claude Haiku 4.5 if you need massive context retention or programmatic enforcement via tools (200,000-token window; tool_calling 5), and you can accept higher output cost ($5.00 per mTok). Note: both scored 3/5 on our constrained_rewriting benchmark and share rank 31 of 52 — this recommendation rests on supporting proxy metrics and cost differences.