Is GPT-5.6 Terra or Grok 4.6 cheaper?

Grok 4.6 is cheaper on all three of the workload shapes tested. On a RAG workload of 12k input and 700 output tokens at 50,000 requests per month with 60% caching, GPT-5.6 Terra costs $972.00 per month and Grok 4.6 costs $870.00. Headline rates are $2/$12 versus $2/$6 per million input/output tokens.

GPT-5.6 Terra vs Grok 4.6

Grok 4.6 is the cheaper of the two across every workload shape tested below. Headline rates are $2 in / $12 out for GPT-5.6 Terra versus $2 in / $6 out for Grok 4.6, per million tokens.

Real monthly cost, three workloads

Workload	GPT-5.6 Terra	Grok 4.6	Cheaper
Support chatbot 1.5k in / 400 out · 100k req/mo · 30% cached	$699.00	$472.50	Grok 4.6 (1.5× cheaper)
RAG / doc Q&A 12k in / 700 out · 50k req/mo · 60% cached	$972.00	$870.00	Grok 4.6 (1.1× cheaper)
Coding agent 25k in / 2.5k out · 20k req/mo · 80% cached	$880.00	$700.00	Grok 4.6 (1.3× cheaper)

Costs include prompt caching at the stated hit rate and per-model tokenizer correction. Adjust for your own traffic →

Specifications side by side

	GPT-5.6 Terra	Grok 4.6
Provider	OpenAI	xAI
Input / M tokens	$2	$2
Output / M tokens	$12	$6
Cached input	$0.2	$0.5
Context window	1050K	500K
Batch discount	−50%	—
Tokenizer factor	×1	×1
Min prefix to cache	—	—
Announced retirement	—	—

Which should you pick?

On cost alone, Grok 4.6 wins every workload shape above.

Full detail: GPT-5.6 Terra · Grok 4.6

All figures verified 2026-08-18 against official provider documentation. Fields a provider does not publish are shown as “—” rather than estimated.