DeepSeek released V4.1-Flash-1017 on October 17 as an update to its Flash model. Its change log says the update cuts task runtime and output length. It lists 11 benchmark scores, including 42.3 on Terminal-Bench 4.0.
Developers can use it through DeepSeek’s API or a service like OpenRouter. Because it’s an open-weight model, they can also download it from Hugging Face and run it on their own servers. I tested it through OpenRouter on DeepSeek’s own servers, at DeepSeek’s prices.
DeepSeek’s model card compares the update with several rivals, but not Haiku 5.5, so I picked it for this hands-on comparison. Anthropic launched Claude Haiku 5.5 on October 7 as its fastest model at standard speed, aimed at high-volume tasks such as classification, summarization, and database queries.
Anthropic notes that its Opus models run faster in Fast Mode. Anthropic reports 39.2 on Terminal-Bench 4.0, 3.1 percentage points below DeepSeek’s reported score. These are vendor-reported results, rather than a controlled head-to-head test.
Haiku costs $0.10 per million input tokens and $0.50 per million output tokens for prompts up to 100,000 tokens, then $0.50 and $2.50 above that. DeepSeek’s off-peak rates are $0.15 per million uncached input tokens, $0.003 per million cached input tokens, and $0.60 per million output tokens; peak rates are twice those amounts.
Comparing uncached input and output rates, Haiku is cheaper on short prompts, and DeepSeek is cheaper on long ones. Actual charges also depend on tokenization, caching, and the provider route.
I built three tests around what each company says its model does well to see which one performs better in practice.
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