Why is Grok so much cheaper?
xAI is pricing to win volume. Grok 4.3 lists at $1.25/Mtok input and $2.50/Mtok output; GPT-5.5 lists at $5 and $30. On output tokens that's a 12x difference, one of the largest gaps between models that plausibly compete at the same tier.
The monthly math is stark. A workload of 1M input and 200K output tokens per day costs about $330/month on GPT-5.5 and about $52/month on Grok 4.3. At that ratio you can run Grok experimentally on full production traffic for less than a sixth of what GPT-5.5 costs, which is exactly what we'd suggest doing before believing anyone's benchmark claims, including ours.
Where does the 30K output cap bite?
Grok 4.3's output tops out at 30K tokens per response; GPT-5.5 allows 128K. For chat, classification, extraction, summarization, and most agent substeps, 30K is plenty; responses in those workloads rarely clear a few thousand tokens.
It bites on single-shot long-form generation: full reports, large code files, document drafting in one pass. If that's a core workload, the cap is disqualifying, not inconvenient. Chunking a 100K-token artifact into four 25K responses is possible but adds stitching logic and failure modes you didn't have before.
There's a second input-side gap: GPT-5.5 reads PDFs natively; Grok takes text and images only. Document-heavy pipelines need a text-extraction stage in front of Grok.
Is Grok's quality actually competitive?
Both models are reasoning models with 1M-class context and tool calling, and on everyday text tasks Grok 4.3 holds its own. The honest caveat is maturity: OpenAI's tool-calling behavior, SDKs, eval ecosystem, and operational track record are more battle-tested than xAI's. For a paid product where a malformed tool call is a customer-visible bug, that maturity is worth real money. For internal tooling, batch processing, and cost-sensitive features, it's worth much less than 12x.
Which should you run?
Pick GPT-5.5 if:
- Single responses regularly need to be very long
- You ingest PDFs directly
- Tool-calling reliability is customer-facing
Pick Grok 4.3 if:
- Your responses stay comfortably under 30K tokens
- Volume makes 12x-cheaper output decisive
- You can absorb the occasional rough edge of a younger ecosystem
At these prices, the experiment costs almost nothing: mirror a slice of production traffic to Grok, diff the outputs, and let your own data make the call.