Claude Haiku 4.5 vs Devstral 2 2512 for Structured Output

Structured Output evaluates JSON schema compliance and format adherence. There is no external benchmark for this task in the payload, so our internal structured_output scores are the primary signal. Devstral 2 2512 scores 5 on structured_output (tied for 1st among 52 models) while Claude Haiku 4.5 scores 4 (rank 26 of 52). Important capabilities for this task are strict format adherence (schema compliance), deterministic formatting under constraints, and stable handling of long contexts when outputting nested structures — all reflected by the structured_output metric in our suite. Supporting metrics explain tradeoffs: Claude Haiku 4.5 scores higher on tool_calling (5 vs 4), faithfulness (5 vs 4), and classification (4 vs 3), indicating it may better integrate with function-calling pipelines and preserve source fidelity. Devstral's top structured_output score shows it is more reliable at producing exactly valid JSON according to our tests.

1. API response generation for billing systems: Devstral 2 2512 (structured_output 5) produces strictly valid JSON schemas and is cheaper at $2/mTok output — ideal for high-volume production. 2) Configuration file authoring with nested schemas: Devstral's 256K context window and 5/5 structured_output help maintain schema correctness across large outputs. 3) Function-argument generation for tool chains: Claude Haiku 4.5 (tool_calling 5, faithfulness 5) is better when the AI must pick the right function and populate arguments precisely, despite scoring 4/5 on structured_output. 4) Classification + structured response routing: Claude Haiku 4.5's classification 4 vs Devstral's 3 favors it when outputs must be both categorized and formatted. Each example mirrors the numeric gaps in our tests (structured_output 5 vs 4; tool_calling 5 vs 4; faithfulness 5 vs 4) and includes cost tradeoffs ($5 vs $2 per output mTok).

For Structured Output, choose Claude Haiku 4.5 if you need stronger tool calling, higher faithfulness, or better built-in classification as part of a multi-step pipeline and are willing to pay higher output costs. Choose Devstral 2 2512 if strict JSON schema compliance, top-ranked structured_output performance (5 vs 4), larger context window, and lower output cost ($2 vs $5 per mTok) are your priorities.