Migrate from Sanity

There is no Sanity importer. Export documents (GROQ or a dataset export), then write Objects.

await cosmic.objects.insertOne({
  title: doc.title,
  type: 'posts',
  slug: doc.slug?.current,
  metadata: {
    content: markdownFromPortableText(doc.body),
  },
});

markdownFromPortableText is your converter. Cosmic rich text is markdown with optional block shortcodes, documented in Rich text.

Image assets upload through Media. Create referenced documents before the documents that point at them.