How to choose an LLM API for agents
An agent makes multiple model calls to finish a task. Choosing its API means checking the entire sequence: tool calls, retries, context growth, provider failures and the final bill. Start with the LLM router decision guide and compare candidates on the same representative tasks.
Map the features your agent actually uses
List streaming, tool calling, structured outputs, images and context requirements. Look up each exact model in the live catalog. OpenAI-compatible request syntax helps integration, but it does not mean every model or provider supports every feature. Follow the agent setup guide for the endpoint and integration instructions.
Keep fallback behavior inside your policy
Decide which providers are eligible and whether an unavailable route should fail or fall back. Check privacy requirements on every eligible route, including retries. A provider's country and a model developer's country are separate facts; use the model and serving-provider directory when jurisdiction matters.
For DeepSeek workloads, use the private DeepSeek API evaluation checklist. For authorized security analysis, the uncensored DeepSeek cyberdefense guide covers a distinct modified checkpoint and practical evaluation prompts.
Set an application budget before expanding the loop
Create separate API keys for projects or agents and configure programmable spend controls. Daily, weekly, monthly and lifetime limits support different operating budgets. Strict admission can count in-flight cost estimates, but final provider usage can exceed an estimate. Also bound tool iterations and retries in your application so a broken loop does not keep producing work.
Compare cost per completed task
Record total input and output tokens across the whole run, retries, completion time, tool errors and whether the result passes your review. A cheap request that needs several repairs may cost more than a reliable response. Keep evaluation cases fixed while changing one routing decision at a time.
Migrate with a representative test set
If you are switching gateways, use the OpenRouter alternatives comparison to shortlist options and the migration guide to test endpoint, authentication and routing differences. Verify failures as well as successes: a timeout, exhausted budget and unavailable provider should leave the agent in a recoverable state.