Is GPT-5.6 Terra or DeepSeek V4 Pro cheaper?

DeepSeek V4 Pro 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 DeepSeek V4 Pro costs $471.24. Headline rates are $2/$12 versus $1.32/$3.96 per million input/output tokens.

GPT-5.6 Terra vs DeepSeek V4 Pro

DeepSeek V4 Pro 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 $1.32 in / $3.96 out for DeepSeek V4 Pro, per million tokens.

Real monthly cost, three workloads

Workload	GPT-5.6 Terra	DeepSeek V4 Pro	Cheaper
Support chatbot 1.5k in / 400 out · 100k req/mo · 30% cached	$699.00	$298.98	DeepSeek V4 Pro (2.3× cheaper)
RAG / doc Q&A 12k in / 700 out · 50k req/mo · 60% cached	$972.00	$471.24	DeepSeek V4 Pro (2.1× cheaper)
Coding agent 25k in / 2.5k out · 20k req/mo · 80% cached	$880.00	$347.60	DeepSeek V4 Pro (2.5× 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	DeepSeek V4 Pro
Provider	OpenAI	DeepSeek
Input / M tokens	$2	$1.32
Output / M tokens	$12	$3.96
Cached input	$0.2	$0.044
Context window	1050K	1000K
Batch discount	−50%	—
Tokenizer factor	×1	×1
Min prefix to cache	—	—
Announced retirement	—	—

Which should you pick?

On cost alone, DeepSeek V4 Pro wins every workload shape above.

Full detail: GPT-5.6 Terra · DeepSeek V4 Pro

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