Yes. ChatGPT's prompt box is a ProseMirror editor on the extension's verified-working list: blanks, transforms, and word cues all run there, with fills landing as a single undo entry. Like claude.ai's composer, it is configured plain-text-only, so text styling is the one thing that no-ops.
The point: better prompts before you spend the turn
A prompt to ChatGPT is exactly the kind of text OpenCues exists for. improve prompt _ re-renders your draft in place before you submit it; fix the grammar _ and make this more formal _ polish it; word cues dim vague words and offer alternatives you cycle with two keys. You iterate on the prompt inside the prompt box, then press Enter yourself. OpenCues never submits anything.
Lookups without losing your thread
Mid-prompt facts stop costing a conversational turn (or a tab switch): capital of france _, 5 miles in km = _, 2024 in roman numerals is _ resolve inline via the fluid blank, and live-data blanks like weather london _ or nvda _ work in the same box. If a blank can't resolve, the _ just stays visible; nothing breaks the draft.
What doesn't work, honestly
ChatGPT's composer rejects programmatic styling, so make X bold _ is typically a silent no-op: OpenCues strips the ** markers (you never see literal asterisks) but the editor won't render the bold. Since you're writing a prompt rather than a document, this rarely matters; if you need rendered styling, use a surface like Gmail. Undo is solid: the write path fires a replacement event ProseMirror treats as one transaction, verified atomic on ChatGPT, so Ctrl+Z restores your pre-fill draft in one step.
Isn't it odd to use AI inside ChatGPT?
Less than it sounds. The model you're addressing answers after you submit; OpenCues works while you compose, on your own key and provider, with sub-second inline latency. The two occupy different phases of the interaction: one is the conversation, the other is steering the prompt before it goes out. That's also why OpenCues works identically in claude.ai, Gemini, and any other chat product's compose box.
Related: Stop copy-pasting from ChatGPT · The Chrome extension · OpenCues on claude.ai · GitHub repo