BYOK vs BYO subscription: compare the whole agent bill

BYOK means supplying an API key and paying through the API account; bring your own subscription means using a supported login route backed by an existing plan. Neither is automatically cheaper. Compare the app fee, the subscription cost you actually add, API charges and paid fallback for the same completed work.

Checked 2 November 2026. This is a whole-workflow budgeting worksheet, not another model-price ranking. For Claude token-rate calculations, use our subscription-versus-API cost guide. For the term itself, see what BYO subscription means.

What changes when you switch from a key to a login?

The funding route changes, not just the sign-in screen. OpenAI's Codex authentication documentation distinguishes ChatGPT subscription access from API-key usage billed through OpenAI Platform. Its billing guide says ChatGPT and API billing are managed separately.

Do not assume that selecting a GPT or Claude model establishes which account pays. Inspect the provider, authentication mode and usage destination. Conductor's FAQ, for example, says it normally uses credentials already saved on the machine, with an API-key override available. The same app can therefore have different billing routes.

Subscription compatibility also depends on the provider's rules. Anthropic's legal guidance permits an end user to sign into the unmodified Claude Code binary with their own subscription in supported hosting arrangements. It does not permit third-party developers to collect Claude session credentials or route their own applications through consumer-plan tokens. A copied OAuth token is not a legitimate substitute for an API key.

Which costs belong in the comparison?

Use two views: incremental cash cost, which answers what changing workflow adds, and fully allocated cost, which includes subscriptions you already pay for. Keep both visible so an existing plan is not described as free.

Cost line	API-key route	Supported subscription route
App software or seat	Include any required fee	Include any required fee
Model inference	Net API charges after usable credits	Included capacity, then authorized extra usage
Other services	Search, hosting, storage and connectors	Same services still need funding
Overflow or fallback	Additional API spend	Separate credits or API spend if enabled
Existing subscription	Include if retained	Include; distinguish new from already paid

A plan login does not pay every connected service. Nor does BYOK remove the application's own charges. Cursor's own-key documentation currently separates individual plans from Teams and Enterprise: eligible team own-key requests can carry a Cursor Token Rate in addition to the provider's model charge. Its documented rate is USD0.25 per million tokens, with model exclusions. Check your plan and eligible models before applying that number.

The same page says Cursor's Zero Data Retention policy does not apply to own-key requests. Billing choice can also change the data-handling assumptions your team needs to review.

How does a worked multi-service budget compare?

Consider a fictional month with the same finished coding tasks and service requirements. These are invented budget inputs for arithmetic, not current app prices, measured usage or customer savings. Assume the subscription route has sufficient included capacity for those tasks.

Monthly line, USD	API-key workflow	Subscription workflow
App fee	12	18
New model subscription needed for this workflow	0	30
Net model API charge	42	0
Separate search service	6	6
Hosting	5	5
Authorized paid fallback	0	8
Total incremental cash cost	65	67

Here, avoiding the USD42 API line does not make the subscription workflow cheaper: its extra software, plan and fallback costs produce a USD67 total versus USD65.

Now suppose you already keep that hypothetical USD30 subscription for unrelated work and would pay for it either way. The subscription workflow adds USD37; the API workflow still adds USD65. For a fully allocated view, add the retained USD30 to the API workflow too: USD95 versus USD67. The ranking depends on the baseline, so declare it before quoting savings.

Capacity is a condition, not an accounting trick. If a plan cannot finish the same work within your deadline, record the extra paid usage or the unfinished tasks. Do not compare a completed API workload with a cheaper subscription workload that stopped halfway through.

How should you count included API credits?

Treat them as a separate funding instrument, not unlimited API entitlement. Anthropic's current credit documentation includes eligible Max, Ultra and Team plans, with claim and organization-linking requirements. It excludes Pro and says unused monthly credits expire.

For a hypothetical USD42 eligible API bill with USD20 of applicable unexpired credit, enter USD22 as the net API charge. Do not subtract the credit again from the subscription price or apply it to search and hosting. Track the gross usage as well so next month's budget is not built around a credit that may be unavailable.

Anthropic says these credits do not change interactive Claude, Claude Code or Cowork limits. When credits run out, purchased credit or auto-reload can fund continued API usage; without other credit, requests stop. Review that behavior before leaving an agent unattended.

What should you verify before committing to either route?

Run a small representative task, then compare the app's selected provider with the provider's billing or usage dashboard. Record the date, task result, credential mode and charged account without saving a secret. Include failed retries and auxiliary services in the worksheet.

Use apps on your ChatGPT plan and apps on your Claude plan to shortlist compatible tools. OpenCode and Conductor illustrate different supported setups; verify their provider documentation and FAQ rather than assuming every harness accepts every plan.

Choose the route that funds your actual workflow with acceptable limits and data handling. Recheck after a plan, provider or authentication change. A budget comparison expires when the route paying for the work changes.