sveltejs/kit · error · Error

Unsupported runtime: ${key}. Supported runtimes are: ${valid

Error message

Unsupported runtime: ${key}. Supported runtimes are: ${valid_runtimes.join(', ')}. See the Node.js Version section in your Vercel project settings for info on the currently supported versions.

What it means

The adapter validates the configured `runtime` value against the list of runtimes Vercel currently supports (nodejs22.x, nodejs24.x, bun1.x). An unrecognized value in the adapter config causes this throw at resolve_runtime time.

Source

Thrown at packages/adapter-vercel/utils.js:115

		}

		return `nodejs${/** @type {22 | 24} */ (major)}.x`;
	}

	throw new Error(
		'Could not auto-detect a runtime. Please explicitly specify a runtime in your adapter configuration.'
	);
}

const valid_runtimes = /** @type {const} */ (['nodejs22.x', 'nodejs24.x', 'bun1.x']);

/**
 * @param {string} key
 * @returns {asserts key is RuntimeKey}
 */
function assert_is_valid_runtime(key) {
	if (!valid_runtimes.includes(/** @type {RuntimeKey} */ (key))) {
		throw new Error(
			`Unsupported runtime: ${key}. Supported runtimes are: ${valid_runtimes.join(', ')}. See the Node.js Version section in your Vercel project settings for info on the currently supported versions.`
		);
	}
}

/** @typedef {typeof valid_runtimes[number]} RuntimeKey */

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Change the `runtime` value in svelte.config.js to a supported one: 'nodejs22.x', 'nodejs24.x', or 'bun1.x'
2. Remove the runtime option entirely to let the adapter auto-detect
3. Check the Node.js Version section of your Vercel project settings for currently supported versions

Example fix

// before
adapter: adapter({ runtime: 'nodejs18.x' })
// after
adapter: adapter({ runtime: 'nodejs22.x' })

const valid = ['nodejs22.x', 'nodejs24.x', 'bun1.x'];
if (!valid.includes(adapterOptions.runtime)) {
  throw new Error(`runtime must be one of ${valid.join(', ')}`);
}

When it happens

Trigger: `resolve_runtime` calls `assert_is_valid_runtime` with a `runtime` option that is not one of 'nodejs22.x', 'nodejs24.x', 'bun1.x'.

Common situations: Upgrading the adapter after Vercel dropped older runtimes (e.g. still configured with nodejs18.x or nodejs20.x), typos like 'node20.x', or copying config from an outdated guide.

Related errors

• Could not auto-detect a runtime. Please explicitly specify a
• Warning: vercel.json defines cron tasks that use paths that
• Invalid value for environment variable ${name}: ${JSON.strin
• The `edge` runtime is no longer supported
• Could not find entry point

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/528bd4024dcf63f8. Report an issue: GitHub.