Use cases

Choosing an AI API for AI agents

Agents call tools in a loop — searching, reading files, running code — so a single task can take dozens of requests. Tool-calling reliability and total cost per task matter most.

What AI agents needs

Reliable tool/function calling
Good planning over many steps
A budget ceiling per task

Models that fit

Model	Maker	List price (in / out per 1M)	Through Somnus	Why
Claude Sonnet 5	Anthropic	$2 / $10	$1 / $5	reliable tool use at a mid price
Claude Opus 5.5	Anthropic	$4 / $20	$2 / $10	long, complex tasks
GPT-5.6 Sol	OpenAI	$5 / $30	$2.5 / $15	alternative strong planner

Somnus column uses the minimum 2× credit; larger top-ups go further.

Cost example

1,000 requests of about 1,500 input and 400 output tokens on Claude Sonnet 5 cost about $7.00 at list price — roughly $3.50 with Somnus credit.

Tips

Give each tool a precise name and JSON schema.
Stop the loop after a fixed number of steps.
Use a cheap model for simple sub-steps and a strong one to plan.

Common mistakes

Unbounded loops that keep calling tools.
Vague tool descriptions that cause wrong calls and retries.

Example

python

from openai import OpenAI
import os

client = OpenAI(
    api_key=os.environ["SOMNUS_API_KEY"],
    base_url="https://gateway-production-c837.up.railway.app/v1",
)

resp = client.chat.completions.create(
    model="claude-sonnet-5",
    messages=[
      {"role": "user", "content": "What's the weather in Lisbon right now?"}
    ],
    tools=[{
        "type": "function",
        "function": {
            "name": "get_weather",
            "description": "Current weather for a city",
            "parameters": {"type": "object", "properties": {"city": {"type": "string"}}, "required": ["city"]},
        },
    }],
)
print(resp.choices[0].message.tool_calls)

Questions

What is the cheapest model for AI agents?

Of the models suggested here, Claude Sonnet 5 has the lowest list price ($2 / $10 per 1M tokens). Test it on your own examples before committing.

Can I switch models later?

Yes. With Somnus you change the model name; the rest of the code stays the same.

Run this code with free credit

Create an account and get $5 of free API credit — enough to try every example on this page.

Get $5 free credit

AI agents in Python with an AI API Cheap Claude API — every Claude model at half price AI API for coding Claude Fable 5.1 vs GPT-5.6 Sol pricing

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