Rename systemPrompt to systemInstruction? Deprecate in favor of initialPrompts?

[michaelwasserman]

WDYT about https://crbug.com/381974893 to rename systemPrompt to systemInstruction for alignment with existing lingo?

Also, should this DOMString systemPrompt; member of dictionary LanguageModelCreateOptions be converted to a LanguageModelMessage type (ideally a union of LanguageModelMessage and LanguageModelMessageShorthand) to support other modalities?

Going a step further, should we just remove this member, since it's a less-capable shorthand for a role: "system" + type: "text" entry in initialPrompts?

LanguageModel.create({ systemPrompt: "Pretend to be an eloquent hamster." });

is equivalent to:

LanguageModel.create({ initialPrompts: [{ role: "system", content: "Pretend to be an eloquent hamster." }]});

and using both raises an exception.

[domenic]

I'm a bit hesitant to use the "system instruction" naming as it's uncommon. As far as I and o3 can tell only, Google uses it in APIs. (One more result in addition to the ones o3 mentions: the Vercel AI SDK uses system in the API and "system prompt" in the docs, like Claude does.)

@KenjiBaheux found an example of a Google API user being confused by this.

In my experience lurking in the community, it's also very common to talk about "system prompts". E.g. look at the volume and topicality of this x.com search for "system prompt" vs. this one for "system instruction".

I think you might be right that it's simplest to just remove the shortcut. It's a bit more verbose, but that sidesteps the naming issue, and removes the special-casing we have to do to prohibit using both. And it gets developers used to the full power of the longhand syntax earlier, which is good because it's more standard across the ecosystem.