Claude Opus 4.8 or Claude Sonnet 5: which to choose?

Side-by-side comparison

Criterion	Claude Opus 4.8	Claude Sonnet 5
Developer	Anthropic	Anthropic
Released	May 28, 2026	June 30, 2026
Capability index	83.4 / 100	79.3 / 100
Input price	$5	$2
Output price	$25	$10
Cost of a typical task	$0.15	$0.06
Context window	1,000,000 tokens	1,000,000 tokens
Maximum output	128,000 tokens	50,000 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, PDF	text, image, PDF
Open weights	No	No
Knowledge cutoff	January 2026	January 31, 2026

Two models head to head

Claude Opus 4.8 and Claude Sonnet 5 are two mid-range models, balancing quality and cost, both built by Anthropic. Claude Opus 4.8 was released on May 28, 2026, Claude Sonnet 5 on June 30, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

What the benchmarks say

On our capability index, Claude Opus 4.8 scores 83.4 out of 100 and Claude Sonnet 5 79.3. Claude Opus 4.8 leads by 4.1 points.

On the 5 benchmarks reported for both, Claude Opus 4.8 wins 4 times and Claude Sonnet 5 1:

GPQA Diamond (PhD-level science questions): Claude Opus 4.8 91%, Claude Sonnet 5 90.5%
OTIS Mock AIME (competition mathematics problems): Claude Opus 4.8 98.3%, Claude Sonnet 5 94.7%
FrontierMath (very hard research-level mathematics): Claude Opus 4.8 80%, Claude Sonnet 5 65.6%
FrontierCode (advanced programming tasks): Claude Opus 4.8 46.5%, Claude Sonnet 5 42.7%
APEX-Agents (professional tasks carried out by an agent): Claude Opus 4.8 48.9%, Claude Sonnet 5 54.5%

Which one costs less?

Claude Opus 4.8 costs $5 per million input tokens and $25 per million output tokens; Claude Sonnet 5 costs $2 and $10.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.15 with Claude Opus 4.8 versus $0.06 with Claude Sonnet 5. Claude Sonnet 5 is 2.5 times cheaper, a gap that adds up quickly over 1,000 tasks: $90 difference.

Run the numbers with your own volumes in the agent cost calculator.

Under the hood

Both models have the same context window: 1,000,000 tokens, roughly 1,500 pages.

Reasoning mode: Claude Opus 4.8 yes, Claude Sonnet 5 yes. Tool calling: Claude Opus 4.8 yes, Claude Sonnet 5 yes. Image input: Claude Opus 4.8 yes, Claude Sonnet 5 yes.

Neither publishes its weights: both are used through an API.

Knowledge cutoff: January 2026 for Claude Opus 4.8, January 31, 2026 for Claude Sonnet 5.

In short

Our reading of the data:

Choose Claude Opus 4.8 for a higher capability index.
Choose Claude Sonnet 5 for a lower cost.

This verdict relies on public figures; it does not replace a trial on your own tasks.

Frequently asked questions

Claude Opus 4.8 or Claude Sonnet 5: which is better?

On our index (Epoch AI data), Claude Opus 4.8 scores 83.4 and Claude Sonnet 5 79.3 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

Claude Sonnet 5. To read 20,000 tokens and write 2,000, expect $0.15 with Claude Opus 4.8 and $0.06 with Claude Sonnet 5 (prices as of October 22, 2026).

Which one has the larger context window?

Neither: both accept 1,000,000 tokens.

Can I run Claude Opus 4.8 or Claude Sonnet 5 on my own servers?

No: both are closed models, available through an API.

Claude Opus 4.8 vs Claude Sonnet 5