AI email comparison
OpenAI (ChatGPT) vs Claude (Anthropic) for Email Drafting
OpenAI and Claude are the two models most professionals already reach for when they draft email in a separate tab. Claude usually lands warmer out of the box; GPT-4o is stronger when you give it a long, precise style brief. Neither remembers how you write across sessions, and neither lives in your inbox.
OpenAI (ChatGPT)
The most widely used AI assistant. Most ChatGPT-for-email power users start here, because it's the tool they're already tab-switching to.
OpenAI's consumer product is ChatGPT, but for email drafting the relevant distinction is between the free or Plus web app and the API. Plus subscribers get GPT-4o with custom instructions (a persistent system prompt you write once) and custom GPTs, which some professionals use as a rough style filter, though it requires re-pasting examples of your own writing and rarely holds up across a long thread. The API tier (GPT-4o, GPT-4o mini, and the o-series reasoning models) is what BYOK tools route through: pay per token, no chat history retained between calls unless the calling app manages it. ChatGPT Team and Enterprise add admin controls and a data-training opt-out, relevant for anyone drafting client-sensitive email. The practical gap for email specifically: ChatGPT has no concept of your Gmail or Outlook history, so every draft starts from whatever context you paste in, and default outputs lean toward a recognizable house style that recipients increasingly clock as AI-written.
Strengths for email
- Familiar interface; most users already have an account
- GPT-4o is strong at following complex style instructions
- Huge prompt-engineering community (r/ChatGPT, YouTube tutorials)
- Functions well as a catch-all AI for non-email tasks too
Weaknesses for email
- No persistent memory of your email style across sessions
- Requires manual copy-paste into Gmail or Outlook every time
- Generic outputs unless you write elaborate system prompts
- ChatGPT 'tells' (em-dashes, 'I hope this email finds you well') are widely detectable
Pricing: Free tier available; ChatGPT Plus ~$20/mo
Best for: General AI drafting when you want manual control over every word
Claude (Anthropic)
Anthropic's conversational AI known for longer context windows and a more natural tone. Preferred by many professionals for client-facing writing.
Claude ships as three tiers: Haiku (fast, cheap), Sonnet (the default balance of speed and quality), and Opus (slower, strongest reasoning), all available both through claude.ai and the API that BYOK tools call directly. Claude.ai's Projects feature lets you attach reference documents, say, a folder of your past sent emails, that persist across a project's conversations, which is the closest the consumer app gets to voice matching, though it requires manually curating and re-uploading that reference set rather than learning from your inbox automatically. Anthropic's training approach (Constitutional AI) tends to produce a less clipped, more conversational default tone than GPT-4o, part of why professionals doing client-facing or relationship-sensitive email often prefer it out of the box. The API has no persistent memory between calls: like every other model provider here, voice consistency is the calling application's job, not Claude's.
Strengths for email
- Longer context window that can handle full email threads
- Tends toward warmer, less robotic prose than GPT-4
- Strong at following nuanced tone instructions
- Less prone to the most obvious ChatGPT tells
Weaknesses for email
- Same manual tab-switching problem as ChatGPT
- No Gmail or Outlook integration built-in
- No persistent voice learning across conversations
- Fewer community prompt resources than OpenAI ecosystem
Pricing: Free tier; Claude Pro ~$20/mo
Best for: Professionals who need long-context drafts and prefer Claude's tone
Head-to-head for email
Verdict for email drafting
Pick Claude when relationship tone matters more than prompt engineering. Pick OpenAI when you already have a solid system prompt and want broad ecosystem support. If you are tired of re-pasting that prompt into a chat window, the model choice matters less than putting the model inside Gmail or Outlook with a voice profile built from your sent mail.
Using OpenAI (ChatGPT) or Claude (Anthropic) inside your inbox
ForthWrite Standard and Pro let you route drafts through OpenAI or Anthropic with your own API key. The extension drafts in the reply pane; the voice profile is learned from your sent items, not from a one-time custom instruction you have to maintain.
Both OpenAI (ChatGPT) and Claude (Anthropic) still start cold in a chat tab: no memory of your sentence length, openers, or sign-offs unless you re-paste a system prompt every session. ForthWrite learns from sent mail and drafts in Gmail or Outlook Web so the model choice is a setting, not a workflow.
Draft with the model you prefer, in your voice
Free plan includes voice matching and 10 drafts/week. Standard and Pro unlock BYOK across 9 providers, including the ones on this page.