Free ebook · C# and .NET 10
One Family,Four Tiers
GPT-6 for C# Developers
Choose and call Astra, Sol, Terra and Luna on Azure, with runnable code and real prices, so you stop guessing which model to use.
- Which of the four models to start with, and when to move up or down
- Six working .NET 10 samples you can clone and run
- What each task cost in real runs, not list prices alone
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Four models. One family. One job each.
GPT-6 comes in four tiers that share an API and differ in depth, speed and price. The book shows where each one earns its place in a C# app.
GPT-6 Astra
The deep end
For the hardest reasoning over long documents, where being right matters more than the bill.
GPT-6.1 Sol
The default for agents
The everyday choice for tool-using agents, with the tool loop and approval boundary done properly.
GPT-6.1 Terra
Screens and documents
Reads screenshots and PDF invoices, calls your C# tools and returns typed results.
GPT-6 Luna
The cheap first stage
High-volume triage at a fraction of the cost, escalating only what needs a bigger model.
Real numbers from real runs
Every sample prints its token usage, and the book turns those runs into cost per task.
Measured in October and November 2026 on made-up data. Your numbers will differ; the book shows how to measure your own.
What’s inside
Seven chapters and four appendices, 95 pages, with 7 figures. Prices were checked against Microsoft’s pricing page in November 2026.
- 1One Family, Four TiersHow the models compare, and a routing rule to start from
- 2GPT-6 AstraLong context and heavy reasoning, in C#
- 3GPT-6.1 SolAgents, tools and a real approval boundary
- 4GPT-6.1 TerraScreenshots, PDF invoices and structured output
- 5GPT-6 LunaTriage at volume, caching and when to escalate
- 6The Decisions APITyped answers from a single call on Luna
- 7Putting Them TogetherRoute, measure and escalate across the family
- A–DAppendicesMicrosoft Agent Framework, prices and caching, one-time setup, resources
Who it’s for
- C# and .NET developers adding AI features on Azure
- Teams choosing a model and wanting a cost estimate before they commit
- Anyone tired of Python-only examples
You need the .NET 10 SDK and an Azure resource with a GPT-6 deployment. The appendix walks through the setup.
About the author
I’m Taswar Bhatti. I write practical guides on running AI models and building agents with C# and .NET at taswar.zeytinsoft.com, and every post comes with a sample you can run.
This book gathers those posts into one guide, with the code re-run and the prices re-checked.