Frequently asked questions
Short answers about access, models, billing and limits, each linking to the page with the detail.
Each answer below is the short form of a page that carries the detail.
Questions
Is the Tessen API compatible with the OpenAI API?
Chat completions follow the OpenAI chat format, so OpenAI's client libraries work when pointed at https://api.tessen.ai/v1. Differences: response_format and logprobs are accepted and ignored, GET /v1/models lists a registry rather than your models, image generation is not available, and Tessen publishes no SDK of its own.
How do I get access to Z1, Z1 Code or H1?
They are in a private pilot. Tessen enrolls accounts individually; email hello@tessen.ai from the account you sign in with. An account that is not enrolled receives 400 model_not_found.
Why do I get model_not_found for z1?
Your account is not in the commercial pilot. It is not a billing problem, and adding funds will not change it.
Can I add funds to my wallet?
Not yet. Purchase is disabled for all accounts, and pilot accounts are funded by Tessen with a labelled testing credit that is not a payment and not refundable.
Is Project ZERO Alpha free?
Yes, for enrolled developers, within a daily allowance of 200 requests and 30 requests a minute. It never debits your wallet and never falls back to a paid model. Enrollment is private.
Why was my H1 answer empty?
H1 reasons before it answers, and reasoning tokens count toward max_tokens. If the limit runs out first, the response is HTTP 200 with empty content and finish_reason length, and you are charged for the tokens produced. Raise max_tokens to 1024 or more.
Does Tessen tell me which model served my request?
No. A response names only the family id you requested. Tessen chooses the capacity behind it.
Can I get guaranteed JSON output?
Not through the API: response_format is not enforced. Ask for JSON in the prompt, validate it in your code, and retry. See Structured responses.
Where do I check whether Tessen is up?
At status.tessen.ai, which reports the Tessen site, the Platform and the API with a 90-day history.
Is there a Tessen SDK?
No package is published. Use plain HTTP or an OpenAI-compatible client. See SDK examples.