Claude Sonnet 5 conceals a cost increase behind unchanged token prices

Anthropic launched Claude Sonnet 5 with unchanged token prices compared to its predecessor Sonnet 4.6, but in practice users are paying considerably more per completed task. The model consumes on average around 40 percent more output tokens per task, nearly doubling the actual cost. This emerges from analyses based on the Artificial Analysis Intelligence Index.

It is not the first time Anthropic has applied this mechanism. With the introduction of Opus 4.7, the published token rates formally remained the same, but a new tokenizer split the same text into approximately 30 percent more tokens, resulting in an effective price increase. With Sonnet 5 that pattern repeats itself, now partly also due to the model's more agentic behaviour.

What Sonnet 5 actually costs in practice

The official launch price for Claude Sonnet 5 is $3 per million input tokens and $15 per million output tokens. Until 31 August 2026, a reduced rate of $2 and $10 per million tokens respectively applies. After that date, standard rates will apply.

For comparison: Opus 4.8, Anthropic's more expensive top-tier model, costs $5 per million input tokens and $25 per million output tokens. In the Artificial Analysis Intelligence Index, an average task with Sonnet 5 costs $2.29, compared to $1.97 with Opus 4.8. Measured per task, Sonnet 5 is therefore more expensive than the model that formally sits in a higher price tier.

The cause lies in the higher token consumption. Sonnet 5 uses a new tokenizer and exhibits more agentic behaviour, in which the model works through multiple steps and generates more text along the way. This potentially delivers better results, but also drives up the number of output tokens. For an API user billed per token, only the total tokens consumed count, regardless of the published list price.

Benchmark performance

In the Artificial Analysis Intelligence Index, Claude Sonnet 5 ranks fifth with 53 points. Notably, the model outperforms Opus 4.8 on some agentic tasks, despite sitting in a lower nominal price tier. For applications where the quality of reasoning and multi-step tasks matters, Sonnet 5 positions itself as a serious alternative to the more expensive top-tier model.

Anthropic has designated Sonnet 5 as the default model for the free and Pro subscription tiers of Claude.ai. Users of Max, Team and Enterprise subscriptions also have access to the model. The broad rollout makes Sonnet 5 in practice the most widely used model within the Anthropic ecosystem.

A structural pattern in model updates

The pricing mechanism via token consumption rather than list rates allows providers to raise costs without this being visible in published price lists. For end users and businesses that budget API costs on the basis of per-token rates, this can lead to unexpected invoice increases when a model is updated.

The phenomenon is not exclusive to Anthropic. Other major model providers are also experimenting with tokenizers and generation strategies that influence output volume. However, Anthropic is drawing particular attention in this regard, because the increase across successive models is measurable and consistent.

For developers and businesses that closely monitor their AI costs, this means that comparing token rates alone is insufficient. Anyone switching to a new model would be wise to re-measure the average token output per task type before adjusting budget estimates.

In the broader European and Dutch AI scene, where many startups and scale-ups build their products on APIs from large American model providers, this underscores the vulnerability of cost models that rely on published list prices. Founders and investors who factor cost efficiency into their model selection will increasingly need to account for actual token consumption per task rather than the rates shown on a pricing page.