Getting an API key for BYOK

How to create an Anthropic or OpenAI API key and paste it into Sessionist.

BYOK stands for Bring Your Own Key — instead of using Sessionist's managed proxy, you supply an API key from an LLM provider and Sessionist talks to them directly on your behalf.

If you're on the Lifetime plan or the Free Trial, this is how Sessionist reaches the LLM. We currently support two providers: Anthropic (Claude) and OpenAI (GPT). You only need one — pick whichever you already have an account with.

Sessionist auto-detects which provider you're using from the key itself, so there's no provider dropdown to set.

Anthropic (Claude)

  1. Go to console.anthropic.com.
  2. Sign in or create an account.
  3. Open Settings → API Keys and click Create Key.
  4. Copy the key — it starts with sk-ant-.
  5. Add at least a few dollars of credit under Billing. New Anthropic accounts start with $0 and calls will fail until the account is funded.

Sessionist defaults to Claude Sonnet 4 when it detects an Anthropic key.

OpenAI (GPT)

  1. Go to platform.openai.com/api-keys.
  2. Sign in or create an account.
  3. Click Create new secret key and copy it — it starts with sk-.
  4. Add credit under Billing → Payment methods. OpenAI also requires a funded balance before keys will work.

Sessionist defaults to GPT-4o when it detects an OpenAI key.

Paste the key into Sessionist

  1. Open Sessionist and click the Settings gear.
  2. Paste your key into the API Key field. The provider is detected automatically from the prefix.
  3. Leave Model blank to use the provider default, or override it with a specific model ID (e.g. claude-opus-4-5 or gpt-4.1).
  4. Click Save.

That's it. Sessionist now routes LLM calls directly to your provider — usage shows up on your Anthropic or OpenAI billing dashboard, not in your Sessionist dashboard.

What it costs

You pay the provider directly at their published rates. A typical Sessionist session uses somewhere between a few cents and a couple of dollars of API credit depending on how long you work and which model you choose. Smaller/cheaper models (e.g. Claude Haiku, GPT-4o-mini) cost less but produce noticeably worse results — we recommend the defaults.

Lifetime owners on a managed plan

If you bought Lifetime and you're on Starter or Pro, the managed proxy is used first and your BYOK key kicks in automatically as overflow once monthly credits run out. You don't need to do anything to switch — just save a key and Sessionist handles the rest.

Trouble

  • "Invalid API key" errors — double-check you copied the whole key (no leading/trailing whitespace) and that your provider account has billing set up.
  • Wrong provider detected — only sk-ant- prefixed keys route to Anthropic. Everything else routes to OpenAI. If you're using a third-party reseller key that doesn't match either prefix, it won't work today.

Still stuck? Email support@sessionist.ai