DeepSeek V4 Flash vs GPT-5.3-Codex for customer service replies
GPT-5.3-Codex wins, 98–93
Same 12 customer service replies tasks, marked blind by three rival labs. GPT-5.3-Codex took 3 tasks, DeepSeek V4 Flash took 1, 8 tied. Tested 14 Aug 2026.
Where they differed most
A paying customer asks when dark mode is coming; it is not on the roadmap. Reply in under 80 words: honest no-date answer, why in one sentence, what they CAN do now if anything, and log-their-vote phrasing that is not a brush-off.
Dark mode isn't on our roadmap right now because we're prioritizing core features. In the meantime, you can use your device's system-wide dark mode or a browser extension. I've logged your vote for our team to review.
Thanks for asking—dark mode isn’t on our current roadmap, so I can’t share a date yet. We’re currently prioritizing reliability and core workflow improvements with the highest customer impact. If it helps now, some customers use browser or OS-level dark mode/extension workarounds. I’ve added your account’s vote and notes to the dark mode request list we use in roadmap planning, so your input is directly counted.
Task by task
| Task | DeepSeek V4 Flash | GPT-5.3-Codex |
|---|---|---|
| Refund the easy way | 10 | 10 |
| Say no without weasel words | 10 | 10 |
| Reply to a 1-star review | 10 | 10 |
| The confused customer | 10 | 10 |
| De-escalate a threat | 8 | 8 |
| The feature you won't build | 8 | 10 |
| Apologise for your mistake | 10 | 10 |
| Price rise notice | 8 | 10 |
| Outage update mid-incident | 10 | 10 |
| The wrong customer | 10 | 10 |
| Chargeback rebuttal facts | 10 | 9 |
| Refuse the fake review request | 8 | 10 |
Full receipts: DeepSeek V4 Flash, GPT-5.3-Codex · judges claude-sonnet-5, gemini-3.1-pro-preview, gpt-5.6-terra
Questions people ask
Which is better for customer service replies: DeepSeek V4 Flash or GPT-5.3-Codex?
GPT-5.3-Codex — it scored 98/100 against 93/100 on our 12-task customer service replies suite, winning 3 tasks to 1 with 8 tied. Every answer was marked blind by three judges from three rival AI labs.
How was this tested?
Both models answered the identical published customer service replies tasks. Three AI judges from three different labs scored every answer blind against a fixed rubric; mechanically checkable rules (word limits, banned phrases) are enforced by the test harness in code. The raw outputs and judge verdicts are downloadable.
More customer service replies head-to-heads: GPT-5.3-Codex vs GPT-5.6 Sol · DeepSeek V4 Flash vs GPT-5.6 Sol · GPT-5.3-Codex vs GPT-5.5 · DeepSeek V4 Flash vs GPT-5.5 · GPT-5.3-Codex vs Grok 4.5 · DeepSeek V4 Flash vs Grok 4.5
Full ranking: Best AI for customer service replies · model pages: DeepSeek V4 Flash, GPT-5.3-Codex