Comparison

How much of your writing each AI tool actually ingests

Most AI assistants ingest none of your writing to build a style — they read a description you type — so the practical comparison is between tools that accept a writing sample and tools that accept only instructions.

The question how many samples does it need assumes every tool takes samples. Most do not. Asking the question exposes the split: instructions-only personalisation on one side, sample-based on the other, and corpus-based measurement on a third.

The distinction has a consequence people feel later. Instructions-only personalisation cannot get more accurate as you write more, because writing more does not change the instruction. Corpus-based profiles improve as coverage grows.

ToolInput it accepts for styleImproves as you write more?Source
ChatGPT custom instructionsText you write describing your preferencesNoVendor settings UI
ChatGPT ProjectsProject instructions plus uploaded reference filesOnly if you re-uploadVendor product docs
Claude custom StylesUploaded sample content reflecting how you communicateOnly if you re-uploadanthropic.com/news/styles
Claude ProjectsCustom instructions plus a knowledge base of filesOnly if you re-uploadanthropic.com/news/projects
Gemini GemsInstructions you write, plus files for contextNosupport.google.com/gemini
MyWritingTwinA corpus of your own writing; free tier from 2,000 words for one use caseYes — coverage per audience, medium and languagemywritingtwin.com/pricing
What each tool takes as input for personal style, verified 2026-09-15

Method notes

  • Uploading a file for reference is not the same as measuring a corpus: the model reads the file as context, and no per-author statistics are computed or reported.
  • Vendors change these mechanics without announcement. Re-verify before quoting the table.

Frequently asked questions

How many writing samples does ChatGPT need to learn my style?
ChatGPT does not learn a style from samples through custom instructions; it reads the description you write. You can attach reference documents to a Project, which the model reads as context, but no per-author measurement is produced.
Which assistants accept a writing sample at all?
As of 2026-09-15, Claude's custom Styles is the assistant feature that explicitly invites uploading sample content that reflects how you communicate. Project and Gem knowledge files accept documents, but as reference material rather than as a style measurement.
Is more writing always better?
More coverage is better; more of the same document type is not. A large pile of one register produces a confident profile of that register and a misleading picture of everything else.

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Sources and how to cite this page

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MyWritingTwin. “How much of your writing each AI tool actually ingests.” Last updated 2026-09-15. https://www.mywritingtwin.com/reference/how-much-writing-each-tool-ingests