Use GPT-5 Mini (openai/gpt-5-mini).
o3 is overkill here.
~8.6× cheaper per run.
Which AI model should you use to implement a REST API endpoint?
Why ->
This work needs synthesis and solid coding ability, but it still lives inside a clear task boundary. Moving to a frontier tier usually costs more than the extra reasoning is worth here.
Cost breakdown
| Model | Provider | Tier | Input cost | Output cost | Est. / 1k calls |
|---|---|---|---|---|---|
| GPT-5 Mini openai/gpt-5-mini | Openai | Moderate | $0.000250 | $0.002000 | $1.25 |
| o3 openai/o3 | Openai | Deep | $0.002000 | $0.008000 | $10.80 |
Matched signals
- rest api
- endpoint
- api endpoint
- implement
- build
This recommendation is based on the task description alone. If you are attaching a large codebase, mention it in the input above.
Model pricing: OpenRouter model catalog, retrieved April 17, 2026. Classification: rightmodel ruleset v2.
Related tasks
Build a Webhook Handler Endpoint
ModerateImplement a webhook handler with signature checks, event parsing, and clear retry handling.
Use GPT-5 Mini.
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Use GPT-5 Mini.
Write Unit Tests for Express API
RoutineCreate focused tests for an Express endpoint with predictable request and response cases.
Use Gemini 2.0 Flash.