Last verified 2026-02-11 (left) · 2026-03-12 (right)

Claude Opus 4.5 (Legacy) vs DeepSeek Reasoner — Pricing & Capability Comparison

Claude Opus 4.5 (Legacy) charges $5.00 per million input tokens and $25.00 per million output tokens. DeepSeek Reasoner comes in at $0.55 / $2.19. Context windows span 200K vs 64K tokens respectively.

TL;DR — Quick Comparison

✓DeepSeek Reasoner is cheaper overall: $2.74 per 1M tokens (in+out) vs $30.00 for Claude Opus 4.5 (Legacy) — saves $27.26 per 1M tokens
✓Input pricing: Claude Opus 4.5 (Legacy) $5.00/1M vs DeepSeek Reasoner $0.55/1M
✓Output pricing: Claude Opus 4.5 (Legacy) $25.00/1M vs DeepSeek Reasoner $2.19/1M
✓Context window: Claude Opus 4.5 (Legacy) offers more (200K vs 64K)
✓Use our calculator below to estimate costs for your specific usage pattern

Input price (per 1M)

Claude Opus 4.5 (Legacy)

$5.00

DeepSeek Reasoner

$0.55

DeepSeek Reasoner leads here

Output price (per 1M)

Claude Opus 4.5 (Legacy)

$25.00

DeepSeek Reasoner

$2.19

DeepSeek Reasoner leads here

Context window

Claude Opus 4.5 (Legacy)

200,000 tokens

DeepSeek Reasoner

64,000 tokens

Claude Opus 4.5 (Legacy) leads here

Cached input

Claude Opus 4.5 (Legacy)

$0.500

DeepSeek Reasoner

$0.140

DeepSeek Reasoner leads here

Which one should you choose?

Skip the spreadsheet if you just need the practical takeaway. Use these rules when deciding between Claude Opus 4.5 (Legacy) and DeepSeek Reasoner.

Choose DeepSeek Reasoner if input tokens dominate your bill

DeepSeek Reasoner has the lower input rate, which usually matters most for chat, RAG, classification, and long-prompt workflows where prompt volume stays much larger than generated output.

Choose DeepSeek Reasoner if you generate long answers

DeepSeek Reasoner is cheaper on output tokens, so it tends to win for report generation, coding assistance, reasoning traces, and any workflow where completions are long.

Choose Claude Opus 4.5 (Legacy) if context size is the blocker

Claude Opus 4.5 (Legacy) offers the larger published context window, which is more important than small pricing differences when you need to fit large files, long chats, or multi-document prompts into one request.

Cost comparison for 10K-token workloads

Side-by-side pricing for identical workloads (10,000 total tokens per request) across different distributions.

Scenario	Claude Opus 4.5 (Legacy)	DeepSeek Reasoner	Claude Opus 4.5 (Legacy) cached	DeepSeek Reasoner cached
Balanced conversation 50% input · 50% output	$0.150	$0.0137	$0.128	$0.0117
Input-heavy workflow 80% input · 20% output	$0.0900	$0.0088	$0.0540	$0.0055
Generation heavy 30% input · 70% output	$0.190	$0.0170	$0.177	$0.0158
Cached system prompt 90% cached input · 10% fresh output	$0.0700	$0.0071	$0.0295	$0.0034

Frequently asked questions

Which is cheaper: Claude Opus 4.5 (Legacy) or DeepSeek Reasoner?

DeepSeek Reasoner is cheaper for input tokens at $0.55 per 1M tokens compared to $5.00. For output, DeepSeek Reasoner costs $2.19 per 1M tokens versus $25.00 for Claude Opus 4.5 (Legacy).

What is the cost per 1M tokens for Claude Opus 4.5 (Legacy)?

Claude Opus 4.5 (Legacy) pricing: $5.00 per 1M input tokens and $25.00 per 1M output tokens. Context window: 200,000 tokens.

What is the cost per 1M tokens for DeepSeek Reasoner?

DeepSeek Reasoner pricing: $0.55 per 1M input tokens and $2.19 per 1M output tokens. Context window: 64,000 tokens.

How much does it cost per 1K tokens?

Per 1K tokens: Claude Opus 4.5 (Legacy) costs $0.0050 input / $0.0250 output. DeepSeek Reasoner costs $0.0006 input / $0.0022 output. This is useful for calculating small-scale usage costs.

Which model supports a larger context window?

Claude Opus 4.5 (Legacy) offers 200,000 tokens (200K) versus 64K for DeepSeek Reasoner.

What is the estimated monthly cost for typical usage?

For a typical workload of 10M input + 2M output tokens per month: Claude Opus 4.5 (Legacy) would cost approximately $100.00, while DeepSeek Reasoner would cost $9.88. DeepSeek Reasoner is more economical for this usage pattern.

Do these models support prompt caching?

Claude Opus 4.5 (Legacy) supports prompt caching at $0.500 per 1M cached tokens, reducing costs for repeated context by up to 90%. DeepSeek Reasoner supports caching at $0.140 per 1M tokens, saving up to 75%.

Which model is best for my use case?

Choose DeepSeek Reasoner for cost-sensitive applications with high input volume. Choose Claude Opus 4.5 (Legacy) if you need 200K context for long documents or conversations. Consider prompt caching if you have repeated context. Use our token calculator to model your specific usage pattern.