Overview
Claude Sonnet 5 is Anthropic's agentic mid-tier model from June 30, 2026. DeepSeek V4.1-Flash launched on September 10, 2026 and is served under the API name deepseek-flash. Since October 17, 2026 that name points to the DeepSeek-V4.1-Flash-1017 update.
Pricing
Claude Sonnet 5: $2 per 1M input tokens and $10 per 1M output tokens.DeepSeek V4.1-Flash: cache-miss input is $0.30 per 1M at peak and $0.15 off-peak, output is $1.20 at peak and $0.60 off-peak, and cache-hit input is $0.006 at peak. Peak hours are 01:00–04:00 and 06:00–10:00 UTC on weekdays.Capabilities
Both models have a 1M-token context window. DeepSeek lists a 384K max output against 128K for Sonnet 5.V4.1-Flash supports thinking and non-thinking modes, vision input, JSON output, tool calls, and OpenAI- and Anthropic-compatible APIs.DeepSeek describes V4.1-Flash as a 552B-parameter MoE using a Causal Encoder–Decoder design that activates 8B parameters for input and 16B for output. Anthropic does not publish parameter counts for Claude.DeepSeek's paper says model checkpoints are published, so the model can be self-hosted. Claude Sonnet 5 is only available through Anthropic and its cloud partners.Benchmarks
DeepSeek reports DeepSWE v1.1 at 77.0 and Terminal-Bench 4.0 at 42.3 for the 1017 update. Anthropic has not published Sonnet 5 scores on those benchmarks, so a direct comparison isn't possible.
Status
Sonnet 5 is now a legacy model. Anthropic's current Sonnet is Sonnet 5.5, at the same price.
No hands-on testing was conducted for this comparison. Every figure above comes from the official pages listed under Research sources, as published on or before October 22, 2026. Where a vendor has not published a number, we say so instead of estimating it.