Claude Haiku 4.5 vs Gemini 2.5 Flash Lite for Structured Output

What Structured Output demands: precise JSON schema compliance, strict format adherence, predictable field ordering/typing, and reliable error handling when inputs are out of spec. Our structured_output benchmark is defined as "JSON schema compliance and format adherence." In our testing both Claude Haiku 4.5 and Gemini 2.5 Flash Lite score 4/5 on that benchmark and share rank 26 of 52. Supporting capabilities that matter here are tool_calling (selecting and populating function args), faithfulness (avoiding hallucinated fields), long_context (handling lengthy prompts with schemas/examples) and the API parameters that enforce format (response_format, structured_outputs). Both models score 5/5 on tool_calling and faithfulness and support structured_outputs and response_format parameters in the payload. Operationally, context window and modality affect implementation: Claude Haiku 4.5 offers a 200,000-token context and text+image->text modality; Gemini 2.5 Flash Lite provides a 1,048,576-token context and text+image+file+audio+video->text modality — both scored 5/5 on long_context in our tests. Because the core structured_output scores are identical, differences in cost ($5.00 vs $0.40 per mTok output), modality, and adjacent capabilities determine which model is more suitable for a given production use case.

1. High-volume API that emits validated JSON responses (status, structured payload): Gemini 2.5 Flash Lite — matches Claude Haiku 4.5's 4/5 structured_output score in our tests but costs $0.40 vs $5.00 per mTok output, delivering large cost savings at scale (12.5× cheaper). 2) Multimodal ingestion that validates schema-driven outputs from files or video transcripts: Gemini 2.5 Flash Lite — supports text+image+file+audio+video->text modality in the payload and ties on structured_output and tool_calling (5/5). 3) Complex decision logic where schema generation depends on nuanced tradeoffs (e.g., scoring, conditional fields, edge-case classification): Claude Haiku 4.5 — in our testing Haiku scores higher on strategic_analysis (5 vs 3) and classification (4 vs 3), which helps when structured output must reflect subtle reasoning. 4) Safety-sensitive schema generation (refusals, allowed exceptions encoded in output): Claude Haiku 4.5 — marginally better safety_calibration in our tests (2 vs 1). 5) Tool-driven workflows that require accurate function argument population: either model — both score 5/5 on tool_calling in our tests, so choose by cost/modality needs.

For Structured Output, choose Claude Haiku 4.5 if you need stronger strategic reasoning, better classification support, or slightly better safety calibration in downstream schema logic despite higher cost. Choose Gemini 2.5 Flash Lite if you want equivalent Structured Output quality in our tests (both 4/5) with far lower output cost ($0.40 vs $5.00 per mTok), larger context, and broader multimodal ingestion.