Claude Opus 4.8 vs GPT-5.3-Codex for workflow automation
GPT-5.3-Codex wins, 90–84
Same 12 workflow automation tasks, marked blind by three rival labs. GPT-5.3-Codex took 5 tasks, Claude Opus 4.8 took 1, 6 tied. Tested 18 Aug 2026.
Where they differed most
The process, as the office manager of a small Bristol removals firm describes it: 'A quote request comes in on the website form. Someone reads it, decides if it is within our area, and if it is we email a price from the ready reckoner. If it is a big job we go and look at it first. If they accept we take a 20% deposit and put it in the calendar, and if the deposit does not arrive within a week the slot goes back.' Reply with ONLY valid JSON — no prose before or after. An object with exactly these keys and no others: trigger (string), steps (an array of objects, each with keys step (number), action (string), automated (boolean), on_error (string)), human_decisions (an array of objects with keys decision (string) and why_human (string)), and open_questions (an array of strings — the things the description does not tell you and that must be answered before this could be built).
```json
{
"trigger": "A quote request is submitted via the website form",
"steps": [
{
"step": 1,
"action": "Receive quote request from website form",
"automated": true,
"on_error": "Log the failed submission and alert office manager to follow up manually"
},
{
"step": 2,
"action": "Read the request and decide whether the job is within the service area",
"automated": false,
"on_error": "If area cannot be determined, contact customer for clarification of location"
},
{…{
"trigger": "A customer submits a quote request through the website form.",
"steps": [
{
"step": 1,
"action": "Capture the website quote request details and create a new enquiry record.",
"automated": true,
"on_error": "If form submission fails or required fields are missing, show an error to the customer and alert staff to review failed submissions."
},
{
"step": 2,
"action": "Review the enquiry to decide whether the move is within the firm's service area.",
"automated": false,
"…Task by task
| Task | Claude Opus 4.8 | GPT-5.3-Codex |
|---|---|---|
| The MOT reminder nobody sends | 9 | 9 |
| The spec, as JSON | 5 | 9 |
| Where the human stays | 8 | 9 |
| The unhappy paths are the job | 8 | 8 |
| Do not automate this | 9 | 8 |
| It fired twice | 9 | 9 |
| The spreadsheet that runs the business | 9 | 9 |
| The alert that wakes someone up | 9 | 10 |
| How long it really takes | 9 | 9 |
| No API, no chance? | 9 | 9 |
| Rules, not guesses | 8 | 9 |
| Refuse the scraper | 9 | 10 |
Full receipts: Claude Opus 4.8, GPT-5.3-Codex · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for workflow automation: Claude Opus 4.8 or GPT-5.3-Codex?
GPT-5.3-Codex — it scored 90/100 against 84/100 on our 12-task workflow automation suite, winning 5 tasks to 1 with 6 tied. Every answer was marked blind by three judges from three rival AI labs.
How was this tested?
Both models answered the identical published workflow automation 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 workflow automation head-to-heads: GPT-5.3-Codex vs GPT-5.6 Sol · Claude Opus 4.8 vs GPT-5.6 Sol · GPT-5.3-Codex vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.6 Luna · Claude Sonnet 5 vs GPT-5.3-Codex · GPT-5.3-Codex vs GPT-5.5
Full ranking: Best AI for workflow automation · model pages: Claude Opus 4.8, GPT-5.3-Codex