Every comparison of ChatGPT and Claude spends its first three paragraphs on writing quality, coding ability, and pricing tiers. Those are real differences, but none of them is the variable that actually decides which one you should open first for a given task. The variable that matters most is what you're about to paste into it.
Start with what you're pasting in, not what comes out
Anthropic (Claude's maker) and OpenAI (ChatGPT's maker) have different postures on caution and refusals, and it shows up in ordinary work, not just edge cases. Ask either one to help draft a termination letter, review a clause in a lease, or summarize a sensitive HR complaint, and you'll sometimes find Claude hedges or adds disclaimers where ChatGPT just answers — and occasionally the reverse. Neither is objectively "better" here; it depends on whether you want a tool that pushes back a little on ambiguous requests or one that assumes good faith and gets out of the way.
The more practical version of this question: which company's data policy are you more comfortable with for what you're about to paste in? If it's a client contract, an unreleased product spec, or anything with real confidentiality stakes, that's worth five minutes of reading each provider's current enterprise/data-retention terms before you paste anything — not a decision to make on vibes.
Document length is a real, practical difference
If your task is "paste in an 80-page PDF and ask questions about it," context window size stops being a spec-sheet number and starts being the difference between one clean pass and manually chunking the document yourself. Claude has generally led on usable context window size for this kind of work. For anything shorter than a few thousand words — most emails, most blog drafts, most single-file code reviews — this difference won't matter to you at all, so don't let it be the deciding factor if your actual documents are short.
Ecosystem breadth vs. writing polish
ChatGPT's advantage is breadth: image generation, voice mode, a large library of custom GPTs, and broader third-party plugin support, all inside one app. If your workflow bounces between "write this," "make an image for this," and "talk this through out loud," ChatGPT's ecosystem means fewer app switches. Claude's advantage is depth in one lane: for long-form writing and editing specifically, its output tends to need less cleanup — fewer generic transitions, less repetition of your own phrasing back at you. If your work is 90% writing and editing, that saved editing time is worth more than breadth you won't use.
You probably don't need to choose
Most people asking "ChatGPT or Claude" are really asking which one to pay $20/month for. Here's the take most comparisons won't give you: don't decide that yet. Both offer genuinely usable free tiers, and unless you're already hitting rate limits daily, you don't have enough data about your own usage pattern to know which subscription would actually earn its cost. Keep both free tabs open for a couple of weeks and route by task — long documents and editing to one, image generation and quick back-and-forth to the other. When you notice yourself hitting a wall on the same tool consistently, you'll know which $20 to spend, based on your actual behavior instead of a comparison article's guess about it.